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UEARTH-000001
1
Nonstationarity of the Hydrological Cycle Under Climate and Environmental Change (UPH 1)
Is the terrestrial hydrological cycle regionally accelerating or decelerating under coupled climate and environmental change, and are there abrupt tipping thresholds in catchment water balance partitioning?
Is the water cycle speeding up or slowing down across different regions as climate and land use change, and does it have tipping points?
Across major hydroclimatic regimes and multi-decadal instrumental records, how do radiative forcing, atmospheric evaporative demand, and land-cover change alter catchment-scale precipitation-runoff-evapotranspiration partitioning ($P - E - Q = \Delta S$), and under what boundary conditions does nonlinear storage-discha...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "budget" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 1); corroborated across Jha et al. (2026) and Tanner et al. (2015). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedroc...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013460", "UEARTH-000015", "UEARTH-019411" ]
[ "10.1080/02626667.2019.1620507", "10.1016/j.htopen.2026.100092", "10.1080/02626667.2015.1052453", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Time Variability and Change (UPH 1), DOI:10.1080/02626667.2019.1620507", "Jha et al. (2026), H2Open Journal, DOI:10.1016/j.htopen.2026.100092", "Tanner et al. (2015), Hydrological Sciences Journal, DOI:10.1080/02626667.2015.105...
UEARTH-000002
2
Cold-Region Runoff and Groundwater Response to Cryospheric Thaw (UPH 2)
How will cold-region catchment runoff generation, seasonality, and subsurface groundwater flow paths reorganize as glaciers retreat, snowpacks diminish, and continuous permafrost degrades?
How will meltwater and groundwater flow change in cold regions as snow, glaciers, and permafrost thaw?
In alpine and high-latitude catchments undergoing snow-to-rain transitions, glacier recession, and active-layer deepening, how does the loss of cryospheric storage and frozen aquitards alter hydraulic connectivity, baseflow recession constants, and peak discharge timing (governed by Kirchner dynamical catchment storage...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain
synoptic_to_seasonal
Holocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "paradoxical rapid mobilization of 'old' pre-event stored water during storm hydrograph peaks" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 2); corroborated across Shi et al. (2026) and Cheng et al. (2018). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedrock...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Pan-Arctic Cryosphere, Greenland, and Boreal Permafros...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013442", "UEARTH-000005", "UEARTH-005323" ]
[ "10.1080/02626667.2019.1620507", "10.1128/aem.00485-26", "10.1029/2017wr021875", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Time Variability and Change (UPH 2), DOI:10.1080/02626667.2019.1620507", "Shi et al. (2026), Applied and environmental microbiology, DOI:10.1128/aem.00485-26", "Cheng et al. (2018), Water Resources Research, DOI:10.1029/2017wr0...
UEARTH-000003
3
Climatic and Catchment Signals in Decadal Flood Regime Changes (UPH 3)
What are the relative causal contributions of synoptic atmospheric circulation shifts, antecedent soil-moisture memory, and land-surface modifications to observed multi-decadal changes in river flood magnitude, frequency, and seasonality?
What controls multi-decadal changes in river flood size, timing, and frequency across different catchments?
Across continental river networks, how do shifts in extreme convective versus stratiform precipitation interact with snowmelt timing, catchment wetness state, and channel-floodplain storage to govern nonstationary flood frequency distributions (governed by master transit-time StorAge Selection (SAS) transport $\partial...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "predictability" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 3); corroborated across Jiang et al. (2023) and Alkama et al. (2010). Remains partially solved due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspirat...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
partially_solved
regional_resolution_only
PARTIAL-PROGRESS
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013461", "UEARTH-013471", "UEARTH-005069" ]
[ "10.1080/02626667.2019.1620507", "10.1016/j.isci.2023.106837", "10.1029/2009jd013408", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Time Variability and Change (UPH 3), DOI:10.1080/02626667.2019.1620507", "Jiang et al. (2023), iScience, DOI:10.1016/j.isci.2023.106837", "Alkama et al. (2010), Journal of Geophysical Research Atmospheres, DOI:10.1029/2009jd013...
UEARTH-000004
4
Land-Cover Change and Soil Feedbacks on Drought Onset and Termination (UPH 4)
How do vegetation structure, rooting depth, and soil hydraulic degradation amplify or dampen the propagation of meteorological drought into agricultural and hydrological drought, and what controls drought termination?
How do changes in land cover and soil properties influence how droughts start, persist, and end?
In water-limited and energy-limited catchments, what nonlinear couplings among canopy stomatal conductance, root-zone water depletion, soil desiccation cracking, and boundary-layer moisture recycling govern the persistence and recovery threshold of multi-year hydrological droughts (governed by Generalized Extreme Value...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
hydroclimatic_extremes_floods_drought_propagation
2
[ "mechanism" ]
[ "hydrosphere_freshwater", "river" ]
[ "freshwater_surface", "groundwater" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
river_basin_or_aquifer
Global and Representative Regional Observatories
interannual_to_decadal
Holocene
[ "multi-decade stream-gauge networks, standardized precipitation/runoff/groundwater drought indices, and satellite altimetry", "coupled land-surface/hydrodynamic routing models and remotely sensed irrigation/reservoir storage records" ]
[ "attenuation, lag time, and nonlinear memory governing meteorological-to-soil-to-groundwater drought propagation" ]
[ "Generalized Extreme Value (GEV) non-stationary return level $G(x; \\mu(t), \\sigma(t), \\xi) = \\exp\\{-[1 + \\xi ((x - \\mu(t))/\\sigma(t))]^{-1/\\xi}\\}$", "runoff-precipitation elasticity $\\varepsilon_Q = (\\bar{P}/\\bar{Q}) (dQ/dP)$ shifting across multi-year drought states" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 4); corroborated across Liu et al. (2024) and Liu et al. (2023). Remains open due to coupled persistent precipitation deficits, extreme atmospheric-river or monsoon rainfall, and human abstraction/impoundment and basin ...
Co-located observations of multi-decade stream-gauge networks, standardized precipitation/runoff/groundwater drought indices, and satellite altimetry and coupled land-surface/hydrodynamic routing models and remotely sensed irrigation/reservoir storage records across Global and Representative Regional Observatories coup...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-014467", "UEARTH-014118", "UEARTH-005199" ]
[ "10.1080/02626667.2019.1620507", "10.1002/eco.2630", "10.1016/j.scitotenv.2023.162771", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Time Variability and Change (UPH 4), DOI:10.1080/02626667.2019.1620507", "Liu et al. (2024), Ecohydrology, DOI:10.1002/eco.2630", "Liu et al. (2023), The Science of the total environment, DOI:10.1016/j.scitotenv.2023.162771", ...
UEARTH-000005
5
Spatial Heterogeneity and Connectivity in Catchment Runoff and Evapotranspiration (UPH 5)
What causes the spatial variability and organization of runoff, evaporation, and subsurface water-flow connectivity across hillslopes and catchments, and how do those patterns violate homogeneous continuum assumptions?
What controls how runoff, evaporation, and underground water pathways vary in space across a watershed?
Across hillslope-to-catchment scales, how do bedrock topography, macropore networks, soil catenas, and aspect-driven radiation gradients organize preferential subsurface flow and evapotranspiration fluxes (governed by master transit-time StorAge Selection (SAS) transport $\partial_t S_T(T, t) + \partial_T S_T(T, t) = J...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "scaling" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 5); corroborated across Zeng et al. (2022) and Wang et al. (2024). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedrock...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
scale_dependent_disagreement
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013658", "UEARTH-013492", "UEARTH-019012" ]
[ "10.1080/02626667.2019.1620507", "10.3390/rs14153628", "10.1016/j.scitotenv.2024.173549", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Space Variability and Scaling (UPH 5), DOI:10.1080/02626667.2019.1620507", "Zeng et al. (2022), Remote Sensing, DOI:10.3390/rs14153628", "Wang et al. (2024), The Science of the total environment, DOI:10.1016/j.scitotenv.2024.17...
UEARTH-000006
6
Upscaling State-Dependent Hydrological Laws Across Spatial Scales (UPH 6)
What are the effective hydrological laws at the catchment scale, and how do they emerge and change with spatial scale from pore-scale Darcy-Richards physics to hillslope and river-basin scales?
What are the physical laws of water flow at the watershed scale, and how do they change with scale?
Can closed-form constitutive relations link catchment-wide storage ($S$) to discharge ($Q$) and evapotranspiration ($E$) across spatial scales ($10^{-3}\,\mathrm{m}$ to $10^{5}\,\mathrm{m}$), or do threshold connectivity and hysteresis prevent scale-invariant parameterizations?
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "scaling" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Holocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "paradoxical rapid mobilization of 'old' pre-event stored water during storm hydrograph peaks" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 6); corroborated across Jha et al. (2026) and Guo et al. (2026). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedrock t...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013452", "UEARTH-013477", "UEARTH-015123" ]
[ "10.1080/02626667.2019.1620507", "10.1016/j.htopen.2026.100092", "10.3390/land15081393", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Space Variability and Scaling (UPH 6), DOI:10.1080/02626667.2019.1620507", "Jha et al. (2026), H2Open Journal, DOI:10.1016/j.htopen.2026.100092", "Guo et al. (2026), Land, DOI:10.3390/land15081393", "B. Arheimer, C. Cudennec,...
UEARTH-000007
7
Bedrock-Controlled Subsurface Flow in the Critical Zone (UPH 7)
Why is most of the water in rivers during floods 'old' pre-event water, and how do deep weathered bedrock and saprolite fractures control transit-time distributions and runoff generation?
Why does floodwater in rivers consist mostly of old underground water rather than fresh rainwater, and what role does deep bedrock play?
In upland catchments, what pressure-wave celerity versus advective velocity mechanisms in the vadose zone, saprolite, and fractured bedrock mobilize pre-event stored water into stream channels during storm events while maintaining long mean transit times (governed by master transit-time StorAge Selection (SAS) transpor...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 7); corroborated across Safeeq et al. (2021) and Shanley et al. (2014). Remains partially solved due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspir...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
partially_solved
dominant_hypothesis_unconfirmed
PARTIAL-PROGRESS
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-000002", "UEARTH-000005", "UEARTH-005624" ]
[ "10.1080/02626667.2019.1620507", "10.1002/hyp.14199", "10.1002/hyp.10377", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Space Variability and Scaling (UPH 7), DOI:10.1080/02626667.2019.1620507", "Safeeq et al. (2021), Hydrological Processes, DOI:10.1002/hyp.14199", "Shanley et al. (2014), Hydrological Processes, DOI:10.1002/hyp.10377", "B. Arh...
UEARTH-000008
8
Soft-Data Constraints on Spatially Distributed Hydrological Models (UPH 8)
How can qualitative hydrological process knowledge, landscape organization, and indirect remote-sensing proxies constrain equifinality and structural uncertainty in spatially distributed hydrological models?
How can field observations of landscape patterns reduce uncertainty when modeling water flow across catchments?
In under-gauged and heterogeneous basins, what information-theoretic combination of hydrochemical tracers, cosmic-ray neutron soil moisture, thermal infrared patterns, and geomorphic organization uniquely identifies subsurface storage-discharge parameters (governed by Kirchner dynamical catchment storage-discharge sens...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "observability" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Holocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "paradoxical rapid mobilization of 'old' pre-event stored water during storm hydrograph peaks" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 8); corroborated across Pan et al. (2023) and Zheng et al. (2025). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedrock...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
framework_dependent
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013688", "UEARTH-000047", "UEARTH-005156" ]
[ "10.1080/02626667.2019.1620507", "10.1016/j.scitotenv.2023.161852", "10.1016/j.jenvman.2024.123939", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Space Variability and Scaling (UPH 8), DOI:10.1080/02626667.2019.1620507", "Pan et al. (2023), The Science of the total environment, DOI:10.1016/j.scitotenv.2023.161852", "Zheng et al. (2025), Journal of environmental managemen...
UEARTH-000009
9
Memory Effects and Extreme Flood Generation in Catchments (UPH 9)
How do catchment memory effects across event, seasonal, and multi-year timescales control the transition from ordinary rainfall-runoff response to catastrophic extreme floods?
How does a watershed's past moisture history trigger extreme, sudden flooding during heavy storms?
What physical threshold in vadose-zone saturation, perched water-table coalescence, and surface-subsurface runoff connectivity causes the storm runoff coefficient to step-change nonlinearly during extreme precipitation events (governed by master transit-time StorAge Selection (SAS) transport $\partial_t S_T(T, t) + \pa...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "predictability" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 9); corroborated across Zeimetz (2017) and Ghanim (2020). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedrock topograp...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013492", "UEARTH-000048", "UEARTH-005547" ]
[ "10.1080/02626667.2019.1620507", "10.5075/epfl-lchcomm-68", "10.17485/ijst/2020/v13i03/121966", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Variability of Extremes (UPH 9), DOI:10.1080/02626667.2019.1620507", "Zeimetz (2017), Infoscience (Ecole Polytechnique Fédérale de Lausanne), DOI:10.5075/epfl-lchcomm-68", "Ghanim (2020), Indian Journal of Science and Technolog...
UEARTH-000010
10
Runoff-Percolation Partitioning Under Megadroughts and Deluges (UPH 10)
Why does runoff-precipitation elasticity shift nonlinearly during persistent multi-year droughts, and how does groundwater-surface water decoupling delay hydrological recovery after drought termination?
Why do some rivers produce much less water than expected during multi-year droughts even when rain returns?
During prolonged hydroclimatic anomalies, how do water-table decline below streambed elevation, root-system plasticity, and vadose-zone hydraulic conductivity reduction induce multi-year hysteresis in annual catchment runoff ratios (governed by Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = ...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "budget" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Holocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "paradoxical rapid mobilization of 'old' pre-event stored water during storm hydrograph peaks" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 10); corroborated across Tanner et al. (2015) and Peng et al. (2026). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedr...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
active_debate
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-000170", "UEARTH-013412", "UEARTH-019294" ]
[ "10.1080/02626667.2019.1620507", "10.1080/02626667.2015.1052453", "10.3390/biology15100811", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Variability of Extremes (UPH 10), DOI:10.1080/02626667.2019.1620507", "Tanner et al. (2015), Hydrological Sciences Journal, DOI:10.1080/02626667.2015.1052453", "Peng et al. (2026), Biology, DOI:10.3390/biology15100811", "B. A...
UEARTH-000011
11
Richards and Saint-Venant Equations Breakdown in Preferential Flow Systems (UPH 11)
Under what field conditions can novel non-Darcian and non-Fickian formulations replace the classical Richards and Saint-Venant equations to represent macropore, film, and preferential subsurface flow?
How can hydrologists replace standard soil-water equations that fail when water flows rapidly through cracks and root channels?
In structured soils and fractured rock where disequilibrium preferential flow dominates over capillary matrix diffusion, what dual-permeability, Stokes-viscous film, or fractional-derivative transport formulation predicts both pressure propagation and solute breakthrough (governed by Budyko hydroclimatic partitioning $...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
vadose_zone_evapotranspiration_ecohydrology
2
[ "mechanism" ]
[ "vadose_zone", "critical_zone" ]
[ "pore_water", "soil" ]
[ "hydrological_partitioning_and_runoff", "ecosystem_disturbance_and_biophysical_feedback" ]
hillslope_to_catchment
Global and Representative Regional Observatories
diurnal_to_synoptic
Anthropocene
[ "cosmic-ray neutron rover soil moisture, eddy-covariance latent heat fluxes, and xylem/soil water stable isotopes", "sap-flow sensors, electrical resistivity imaging of root zones, and SMAP/Sentinel-1 microwave soil moisture" ]
[ "ecohydrological separation ('two water worlds') between tightly bound matrix water used by roots and mobile recharge water" ]
[ "Richards unsaturated flow $\\partial_t \\theta(\\psi) = \\nabla \\cdot [K(\\psi) \\nabla (\\psi + z)] - S_{\\mathrm{root}}(\\psi)$ coupled with Penman-Monteith evapotranspiration $\\lambda E = [\\Delta (R_n - G) + \\rho_a c_p \\mathrm{VPD} / r_a] / [\\Delta + \\gamma (1 + r_s / r_a)]$", "Budyko hydroclimatic par...
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 11); corroborated across Guo et al. (2026) and Cavelan et al. (2025). Remains open due to coupled vapor pressure deficit (VPD), solar radiation, and intermittent rainfall infiltration pulses and soil water retention cur...
Co-located observations of cosmic-ray neutron rover soil moisture, eddy-covariance latent heat fluxes, and xylem/soil water stable isotopes and sap-flow sensors, electrical resistivity imaging of root zones, and SMAP/Sentinel-1 microwave soil moisture across Global and Representative Regional Observatories coupled with...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013971", "UEARTH-013983", "UEARTH-005317" ]
[ "10.1080/02626667.2019.1620507", "10.1021/acsomega.6c02253", "10.1016/j.scitotenv.2025.181070", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces in Hydrology (UPH 11), DOI:10.1080/02626667.2019.1620507", "Guo et al. (2026), ACS omega, DOI:10.1021/acsomega.6c02253", "Cavelan et al. (2025), The Science of the total environment, DOI:10.1016/j.scitotenv.2025.1810...
UEARTH-000012
12
Transient Surface-Groundwater Exchange Across Hyporheic Zones (UPH 12)
What processes control the transient exchange of water, heat, and reactive solutes between river channels and alluvial aquifers across heterogeneous hyporheic zones from riffle to basin scales?
What controls how river water and groundwater mix and react beneath streambeds across different scales?
How do dynamic bedform migration, flood-wave hydrograph unsteadiness, sediment colmation, and bio-clogging modulate hyporheic residence-time distributions and redox zonation from sub-meter bedforms to alluvial valley corridors (governed by hyporheic Damköhler number $\mathrm{Da} = \tau_{\mathrm{res}} k_{\mathrm{rxn}}$ ...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
hyporheic_river_groundwater_lake_wetland
2
[ "mechanism", "feedback" ]
[ "river", "wetland" ]
[ "freshwater_surface", "pore_water" ]
[ "groundwater_flow_and_transport", "hydrological_partitioning_and_runoff" ]
reach
Global and Representative Regional Observatories
synoptic_to_seasonal
Holocene
[ "fiber-optic distributed temperature sensing (FO-DTS), 222Rn/He exchange tracers, and streambed vertical head gradients", "SWOT wide-swath satellite water-surface elevation/slope and wetland inundation hydroperiod maps" ]
[ "multi-scale hyporheic exchange residence-time distributions driven by bedforms, bars, and meandering" ]
[ "hyporheic Damköhler number $\\mathrm{Da} = \\tau_{\\mathrm{res}} k_{\\mathrm{rxn}}$ governing aerobic-to-denitrifying redox transition along bedform streamlines", "1D Saint-Venant transient channel-storage routing $\\partial_t A + \\partial_x Q = q_{\\mathrm{lat}} - q_{\\mathrm{hyp}}(A_s / A) \\partial_t (C_s - ...
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 12); corroborated across Terefe et al. (2026) and Sterte et al. (2018). Remains open due to coupled stage fluctuations, bedform-induced hydrostatic/hydrodynamic pressure gradients, and seasonal water-table shifts and st...
Co-located observations of fiber-optic distributed temperature sensing (FO-DTS), 222Rn/He exchange tracers, and streambed vertical head gradients and SWOT wide-swath satellite water-surface elevation/slope and wetland inundation hydroperiod maps across Global and Representative Regional Observatories coupled with proce...
open
scale_dependent_disagreement
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013801", "UEARTH-013652", "UEARTH-015123" ]
[ "10.1080/02626667.2019.1620507", "10.3390/w18111328", "10.1016/j.jhydrol.2018.03.011", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces in Hydrology (UPH 12), DOI:10.1080/02626667.2019.1620507", "Terefe et al. (2026), Water, DOI:10.3390/w18111328", "Sterte et al. (2018), Journal of Hydrology, DOI:10.1016/j.jhydrol.2018.03.011", "B. Arheimer, C. Cud...
UEARTH-000013
13
Subsurface Processes Governing Baseflow Recession and Streamflow Permanence (UPH 13)
What subsurface aquifer geometries, hydraulic diffusivity contrasts, and riparian evapotranspiration losses control the nonlinear shape of streamflow recession curves and the spatial contraction of perennial stream networks?
What underground processes control how fast rivers dry up between rainstorms and which stream reaches stop flowing?
Across headwater networks, how do power-law recession parameters ($-dQ/dt = aQ^b$) reflect the interplay among unconfined fractured-bedrock drainage, riparian phreatophyte uptake, and longitudinal stream-network disconnection?
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 13); corroborated across Malish et al. (2025) and Tashie et al. (2019). Remains partially solved due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspir...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
partially_solved
multiple_viable_hypotheses
PARTIAL-PROGRESS
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013724", "UEARTH-013448", "UEARTH-005593" ]
[ "10.1080/02626667.2019.1620507", "10.1002/eco.70155", "10.1002/hyp.13530", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces in Hydrology (UPH 13), DOI:10.1080/02626667.2019.1620507", "Malish et al. (2025), Ecohydrology, DOI:10.1002/eco.70155", "Tashie et al. (2019), Hydrological Processes, DOI:10.1002/hyp.13530", "B. Arheimer, C. Cudenn...
UEARTH-000014
14
Long-Term Legacy Contaminant and Nutrient Retention in Catchments (UPH 14)
What biogeochemical and hydrological travel-time mechanisms control the decadal-to-centennial persistence and episodic remobilization of legacy agricultural nutrients and contaminants in catchments?
Why do fertilizers and pollutants remain trapped in soils and groundwater for decades after pollution stops, and what triggers their release?
In agricultural and mixed-use watersheds, how does the coupling between young preferential flow paths, old groundwater age distributions, and vadose-zone geochemical sorption/redox buffers create chemostatic export regimes and multi-decadal lag times (governed by Richards unsaturated flow $\partial_t \theta(\psi) = \na...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
vadose_zone_evapotranspiration_ecohydrology
2
[ "mechanism", "predictability" ]
[ "vadose_zone", "critical_zone" ]
[ "pore_water", "soil" ]
[ "hydrological_partitioning_and_runoff", "ecosystem_disturbance_and_biophysical_feedback" ]
hillslope_to_catchment
Global and Representative Regional Observatories
diurnal_to_synoptic
Holocene
[ "cosmic-ray neutron rover soil moisture, eddy-covariance latent heat fluxes, and xylem/soil water stable isotopes", "sap-flow sensors, electrical resistivity imaging of root zones, and SMAP/Sentinel-1 microwave soil moisture" ]
[ "partitioning of terrestrial evapotranspiration between plant transpiration (T) and soil/canopy evaporation (E)" ]
[ "Richards unsaturated flow $\\partial_t \\theta(\\psi) = \\nabla \\cdot [K(\\psi) \\nabla (\\psi + z)] - S_{\\mathrm{root}}(\\psi)$ coupled with Penman-Monteith evapotranspiration $\\lambda E = [\\Delta (R_n - G) + \\rho_a c_p \\mathrm{VPD} / r_a] / [\\Delta + \\gamma (1 + r_s / r_a)]$", "Budyko hydroclimatic par...
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 14); corroborated across Stockinger et al. (2024) and Sousa et al. (2023). Remains open due to coupled vapor pressure deficit (VPD), solar radiation, and intermittent rainfall infiltration pulses and soil water retentio...
Co-located observations of cosmic-ray neutron rover soil moisture, eddy-covariance latent heat fluxes, and xylem/soil water stable isotopes and sap-flow sensors, electrical resistivity imaging of root zones, and SMAP/Sentinel-1 microwave soil moisture across Global and Representative Regional Observatories coupled with...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-014794", "UEARTH-013706", "UEARTH-014964" ]
[ "10.1080/02626667.2019.1620507", "10.1002/hyp.15038", "10.3389/feart.2022.886304", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces in Hydrology (UPH 14), DOI:10.1080/02626667.2019.1620507", "Stockinger et al. (2024), Hydrological Processes, DOI:10.1002/hyp.15038", "Sousa et al. (2023), Frontiers in Earth Science, DOI:10.3389/feart.2022.886304", ...
UEARTH-000015
15
Coevolution of Catchment Geomorphology, Vegetation, and Hydrology (UPH 15)
What thermodynamic optimality or mechanistic feedbacks govern the long-term coevolution of drainage density, soil depth, root-zone storage capacity, and vegetation water use across climate gradients?
How do plants, soils, and river networks shape each other over decades to millennia to control water flow?
Across aridity and tectonic uplift gradients, do vegetation dynamically optimize root-zone water storage capacity ($S_r$) to survive multi-decadal drought return periods, and how does this coevolutionary feedback constrain Budyko water-energy partitioning?
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "feedback" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 15); corroborated across Rendilicha et al. (2025) and Murgia et al. (2026). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration an...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
dominant_hypothesis_unconfirmed
OPEN-VERIFIED
true
hard
4
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013408", "UEARTH-013393", "UEARTH-005175" ]
[ "10.1080/02626667.2019.1620507", "10.1016/j.ecolind.2025.113652", "10.1016/j.jhydrol.2026.135569", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces in Hydrology (UPH 15), DOI:10.1080/02626667.2019.1620507", "Rendilicha et al. (2025), Ecological Indicators, DOI:10.1016/j.ecolind.2025.113652", "Murgia et al. (2026), Journal of Hydrology, DOI:10.1016/j.jhydrol.2026...
UEARTH-000016
16
Generation and Secular Reversal Mechanics of Earth's Geodynamo (Earth in Time Q1)
How is Earth's magnetic field generated and sustained by thermochemical convection in the liquid iron-nickel outer core, and what magnetohydrodynamic instability triggers geomagnetic excursions and polarity reversals?
How does Earth's liquid outer core generate our planet's magnetic field, and what causes the magnetic poles to flip?
In the rapidly rotating, low-Ekman-number ($\mathrm{Ek} \sim 10^{-15}$), low-magnetic-Prandtl-number ($\mathrm{Pm} \sim 10^{-6}$) liquid outer core, what relative buoyancy contributions from inner-core crystallization latent heat, light-element (Si, O, S, Mg) exsolution, and core-mantle boundary heat-flux heterogeneity...
deep_earth_tectonics_geodynamics_geomagnetism
1
Deep Earth, Tectonics, Geodynamics, and Geomagnetism
core_dynamo_inner_core
1
[ "mechanism", "threshold" ]
[ "inner_core", "outer_core" ]
[ "core_alloy", "melt" ]
[ "geomagnetic_dynamo", "mantle_convection" ]
mantle_or_core_domain
Planetary Deep Interior (Inner and Outer Core)
millennial_to_orbital
Quaternary
[ "PKIKP body-wave travel-time residuals and normal-mode splitting functions", "satellite and paleomagnetic secular-variation field reconstructions" ]
[ "inner-core crystalline anisotropy, light-element partitioning, and outer-core convective buoyancy flux" ]
[ "magnetic induction $\\partial_t \\mathbf{B} = \\nabla \\times (\\mathbf{u} \\times \\mathbf{B}) + \\eta_m \\nabla^2 \\mathbf{B}$ at $\\mathrm{Ek} \\sim 10^{-15}$ and $\\mathrm{Pm} \\sim 10^{-6}$", "Elsasser number $\\Lambda = \\sigma B^2 / (\\rho \\Omega) \\sim O(1)$ and thermochemical buoyancy flux $F_B = F_T +...
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 1); corroborated across Fu et al. (2025) and Sun et al. (2023). Remains open due to coupled inner-core crystallization buoyancy flux and secular core cooling and core-mantle boundary topography and heterogeneous lower-mantle thermal ...
Co-located observations of PKIKP body-wave travel-time residuals and normal-mode splitting functions and satellite and paleomagnetic secular-variation field reconstructions across Planetary Deep Interior (Inner and Outer Core) coupled with process-resolving models of geomagnetic dynamo to constrain inner-core crystalli...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-000391", "UEARTH-001453", "UEARTH-001704" ]
[ "10.17226/25761", "10.1029/2025jb031934", "10.1038/s41467-023-37376-1", "10.17226/25761" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Priority Questions (Question 1), DOI:10.17226/25761", "Fu et al. (2025), Journal of Geophysical Research Solid Earth, DOI:10.1029/2025jb031934", "Sun et al. (2023), Nature Communications, DOI:10.1038/s41467-023-37376-1", "NASEM (2020), A Vision...
UEARTH-000017
17
Initiation Timing and Geodynamic Mechanism of Terrestrial Plate Tectonics (Earth in Time Q2)
When and by what lithospheric weakening and mantle-convection mechanism did Earth transition from a stagnant-lid or sluggish-lid regime to global mobile-lid plate tectonics?
When and how did plate tectonics begin on Earth, and why did Earth develop moving plates unlike Venus or Mars?
Across the Hadean-Archean-Proterozoic rock and zircon archive ($4.4\text{--}2.5\,\mathrm{Ga}$), what combination of mantle potential temperature evolution, grain-size damage rheology, plume-induced subduction initiation, and surface water lubrication overcame lithospheric yield strength to establish sustained global su...
deep_earth_tectonics_geodynamics_geomagnetism
1
Deep Earth, Tectonics, Geodynamics, and Geomagnetism
craton_orogen_continental_crust
1
[ "mechanism", "reconstruction" ]
[ "continental_crust", "orogen" ]
[ "crystalline_rock", "mantle_silicate" ]
[ "crustal_deformation", "metamorphic_transformation" ]
tectonic_plate_or_orogen
Archean–Proterozoic Cratons and Continental Orogens
multi_million_year_tectonic
Precambrian
[ "laser-ablation ICP-MS/SIMS zircon U-Pb geochronology and Lu-Hf isotope ratios", "crustal receiver-function Moho depth maps, Bouguer gravity anomalies, and xenolith thermobarometry" ]
[ "cratonic lithospheric root stability, metasomatic weakening, and orogenic lower-crustal flow" ]
[ "viscous thin-sheet Argand number $\\mathrm{Ar} = g \\rho_c (1 - \\rho_c/\\rho_m) H_c^2 / (\\eta_{\\mathrm{eff}} U_0)$", "isopycnic cratonic root stability $\\Delta \\rho(T, X_{\\mathrm{Mg\\#}}) = \\rho_0 [ -\\alpha (T - T_0) + \\beta_{\\mathrm{chem}} \\Delta X_{\\mathrm{Mg\\#}} ] \\approx 0$" ]
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 2); corroborated across Korenaga (2011) and Wang et al. (2025). Remains open due to coupled continental collision, lithospheric thickening, and convective removal of eclogitized lower crust and Moho temperature, crustal radiogenic he...
Co-located observations of laser-ablation ICP-MS/SIMS zircon U-Pb geochronology and Lu-Hf isotope ratios and crustal receiver-function Moho depth maps, Bouguer gravity anomalies, and xenolith thermobarometry across Archean–Proterozoic Cratons and Continental Orogens coupled with process-resolving models of crustal defo...
open
active_debate
OPEN-VERIFIED
true
very_hard
5
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-000330", "UEARTH-000554", "UEARTH-000020" ]
[ "10.17226/25761", "10.1029/2011jb008410", "10.1038/s43247-025-02973-z", "10.17226/25761" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Priority Questions (Question 2), DOI:10.17226/25761", "Korenaga (2011), Journal of Geophysical Research Atmospheres, DOI:10.1029/2011jb008410", "Wang et al. (2025), Communications Earth & Environment, DOI:10.1038/s43247-025-02973-z", "NASEM (20...
UEARTH-000018
18
Thermochemical Nature and Origin of Large Low-Shear-Velocity Provinces (LLSVPs)
Are the two antipodal Large Low-Shear-Velocity Provinces (LLSVPs) beneath Africa and the Pacific purely thermal megaplume clusters, primordial dense bridgmanite/ferropericlase reservoirs, or accumulations of subducted oceanic crust?
What are the two continent-sized blobs deep in Earth's lower mantle beneath Africa and the Pacific, and how did they form?
At the base of the lower mantle ($2,000\text{--}2,891\,\mathrm{km}$ depth), what combination of normal-mode density tomography, S-to-P wave velocity ratios ($d\ln V_S / d\ln V_P$), and noble-gas ($^3\mathrm{He}/^4\mathrm{He}$, $^{182}\mathrm{W}$) plume signatures distinguishes dense thermochemical piles from thermal up...
deep_earth_tectonics_geodynamics_geomagnetism
1
Deep Earth, Tectonics, Geodynamics, and Geomagnetism
lower_mantle_plumes_transition_zone
1
[ "mechanism", "rate" ]
[ "lower_mantle", "transition_zone" ]
[ "mantle_silicate", "rock" ]
[ "mantle_convection", "metamorphic_transformation" ]
mantle_or_core_domain
Global Mantle Transition Zone and Lower Mantle
multi_million_year_tectonic
Cenozoic
[ "broadband seismic tomography, receiver-function conversions, and shear-wave splitting measurements", "full-waveform seismic tomography and P-to-S receiver-function discontinuity depths" ]
[ "thermochemical density contrasts across Large Low-Shear-Velocity Provinces (LLSVPs)" ]
[ "Clapeyron slope $dP/dT = \\Delta S / \\Delta V$ across the $410\\,\\mathrm{km}$ ($\\gamma > 0$) and $660\\,\\mathrm{km}$ ($\\gamma \\le 0$) phase boundaries", "thermochemical buoyancy ratio $B = \\Delta \\rho_{\\mathrm{chem}} / (\\rho_0 \\alpha \\Delta T)$ and Rayleigh number $\\mathrm{Ra} = \\rho g \\alpha \\De...
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 3a); corroborated across Wang et al. (2020) and Jackson et al. (2018). Remains open due to coupled thermochemical mantle convection and deep slab negative buoyancy and endothermic 660-km phase-transition clapeyron slopes and basal t...
Co-located observations of broadband seismic tomography, receiver-function conversions, and shear-wave splitting measurements and full-waveform seismic tomography and P-to-S receiver-function discontinuity depths across Global Mantle Transition Zone and Lower Mantle coupled with process-resolving models of mantle conve...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-001403", "UEARTH-000311", "UEARTH-002760" ]
[ "10.17226/25761", "10.1038/s41467-019-13720-2", "10.1029/2018gc007552", "10.17226/25761" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Deep Earth Structure (Question 3a), DOI:10.17226/25761", "Wang et al. (2020), Nature communications, DOI:10.1038/s41467-019-13720-2", "Jackson et al. (2018), Geochemistry Geophysics Geosystems, DOI:10.1029/2018gc007552", "NASEM (2020), A Vision...
UEARTH-000019
19
Rheological Controls on the Lithosphere-Asthenosphere Boundary (LAB)
What relative roles do partial silicate melt fractions, grain-boundary water weakening, and elastically accommodated grain-boundary sliding play in producing the sharp seismic velocity drop and low viscosity at the oceanic Lithosphere-Asthenosphere Boundary?
What makes the boundary between Earth's rigid tectonic plates and the softer mantle beneath them so sharp and slippery?
Beneath oceanic plates of varying thermal age ($0\text{--}150\,\mathrm{Ma}$), can broadband ocean-bottom magnetotelluric, receiver-function ($Sp$, $Ps$), and active-source seismic reflection profiles distinguish a volatile-rich partial melt channel from sub-solidus dislocation/diffusion creep transitions at the LAB?
deep_earth_tectonics_geodynamics_geomagnetism
1
Deep Earth, Tectonics, Geodynamics, and Geomagnetism
subduction_slab_mantle_wedge
3
[ "mechanism", "rate" ]
[ "subduction_zone", "upper_mantle" ]
[ "crystalline_rock", "magma_or_melt" ]
[ "plate_subduction", "magma_generation_and_ascent" ]
tectonic_plate_or_orogen
Circum-Pacific and Tethyan Subduction Margins
multi_million_year_tectonic
Cenozoic
[ "deep magnetotelluric (MT) and electrical resistivity tomography (ERT) conductivity inversions", "high-resolution slab-interface seismic attenuation and magnetotelluric conductivity profiles" ]
[ "mechanical coupling and metamorphic dehydration kinetics along the plate interface" ]
[ "composite dislocation-diffusion creep $\\dot{\\varepsilon}_{ij} = (A_{\\mathrm{dis}} \\tau_E^{n-1} + A_{\\mathrm{diff}} d^{-p}) C_{\\mathrm{OH}}^r \\exp[-(E^* + P V^*)/RT] \\tau_{ij}$", "slab thermal parameter $\\Phi_{\\mathrm{slab}} = t_{\\mathrm{age}} v_{\\mathrm{conv}} \\sin\\theta$ governing dehydration reac...
Formulated in Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework (2020, SO-2); corroborated across Wang et al. (2024) and Rychert et al. (2005). Remains open due to coupled slab pull, trench rollback, and metamorphic dehydration reactions and slab thermal age, incoming plate hydration state, and overr...
Co-located observations of deep magnetotelluric (MT) and electrical resistivity tomography (ERT) conductivity inversions and high-resolution slab-interface seismic attenuation and magnetotelluric conductivity profiles across Circum-Pacific and Tethyan Subduction Margins coupled with process-resolving models of plate su...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,020
A. A. P. Koppers, R. Coggon
2026-10-16T00:00:00
[ "UEARTH-000605", "UEARTH-000573", "UEARTH-000082" ]
[ "10.6075/J0W66J9H", "10.1038/s41467-024-47887-0", "10.1038/nature03904", "10.17226/25761" ]
[ "Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework (2020), Oceanic Life Cycle of Tectonic Plates (SO-2), DOI:10.6075/J0W66J9H", "Wang et al. (2024), Nature Communications, DOI:10.1038/s41467-024-47887-0", "Rychert et al. (2005), Nature, DOI:10.1038/nature03904", "NASEM (2020), A Vision for ...
UEARTH-000020
20
Nucleation to Arrest Physics of Large Earthquakes and Fault Slip Modes (Earth in Time Q4)
What physical, frictional, and pore-fluid processes govern the transition from aseismic creep and slow slip events to dynamic seismic rupture nucleation, propagation, and arrest on natural faults?
What determines whether a tectonic fault creeps harmlessly or ruptures in a devastating earthquake, and what stops an earthquake once it starts?
Along heterogeneous subduction megathrusts and continental strike-slip faults, how do rate-and-state friction parameters ($a-b$), dilatant pore-pressure transients, thermal pressurization, and geometrical fault roughness interact across millimeter-to-kilometer scales to control rupture nucleation size and final seismic...
earthquakes_volcanoes_tsunamis_geohazards
2
Earthquakes, Volcanoes, Tsunamis, and Geohazards
earthquake_rupture_fault_mechanics
1
[ "mechanism", "hazard_generation" ]
[ "fault_zone", "continental_crust" ]
[ "crystalline_rock", "pore_water" ]
[ "fault_rupture_and_slip", "crustal_deformation" ]
fault_or_volcanic_edifice
Plate-Boundary and Intraplate Seismogenic Fault Zones
instantaneous_to_event
Holocene
[ "near-field broadband seismograms, high-rate GNSS displacements, and InSAR coseismic interferograms", "fault-zone drilling core microstructure and laboratory rotary-shear friction velocity dependence" ]
[ "rate-and-state frictional healing, dynamic pore-fluid pressurization, and rupture arrest thresholds" ]
[ "rate-and-state friction $\\tau = \\sigma_n' [\\mu_0 + a \\ln(V/V_0) + b \\ln(V_0 \\theta / D_c)]$ with thermal pressurization $\\partial_t P_f = \\Lambda_{\\mathrm{TP}} \\tau V / w + D_{\\mathrm{hyd}} \\partial_{yy} P_f$", "elastodynamic fracture energy balance $G_c = \\int_0^{D_c} (\\tau(u) - \\tau_r) du$ and c...
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 4a); corroborated across Lengliné et al. (2023) and Passelègue et al. (2019). Remains open due to coupled tectonic shear-stress loading and coseismic dynamic pore-pressure transients and fault-zone geometric complexity, gouge mineral...
Co-located observations of near-field broadband seismograms, high-rate GNSS displacements, and InSAR coseismic interferograms and fault-zone drilling core microstructure and laboratory rotary-shear friction velocity dependence across Plate-Boundary and Intraplate Seismogenic Fault Zones coupled with process-resolving m...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-001610", "UEARTH-001540", "UEARTH-000364" ]
[ "10.17226/25761", "10.1029/2022gl101604", "10.1130/g45868.1", "10.25740/hy589fc7561" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Priority Questions (Question 4a), DOI:10.17226/25761", "Lengliné et al. (2023), Geophysical Research Letters, DOI:10.1029/2022gl101604", "Passelègue et al. (2019), Geology, DOI:10.1130/g45868.1", "E. E. Brodsky, T. A. Plank, D. M. Roman et al. ...
UEARTH-000021
21
Transcrustal Magma Storage Architecture and Eruption Triggering Precursors (ERUPT Grand Challenge 1)
How do crystal-rich transcrustal magma mush systems rapidly remobilize into eruptible melt lenses, and what geophysical or volatile-degassing precursors distinguish impending eruptions from failed magmatic intrusions?
How does mostly solid magma deep underground suddenly turn liquid and erupt, and why do some volcanic unrest episodes stop without erupting?
Within transcrustal silicic and mafic magmatic plumbing systems ($2\text{--}30\,\mathrm{km}$ depth), what coupled thermo-mechanical thresholds of mafic recharge, second boiling volatile exsolution, and mush compaction govern eruption onset, and how can joint InSAR, seismic tomography, and $\mathrm{CO}_2/\mathrm{SO}_2$ ...
earthquakes_volcanoes_tsunamis_geohazards
2
Earthquakes, Volcanoes, Tsunamis, and Geohazards
volcanic_plumbing_eruption_degassing
1
[ "mechanism", "hazard_generation" ]
[ "magma_reservoir", "continental_crust" ]
[ "magma_or_melt", "hydrothermal_fluid" ]
[ "volcanic_degassing_and_eruption", "magma_generation_and_ascent" ]
fault_or_volcanic_edifice
Active Arc, Rift, and Hotspot Volcanic Systems
instantaneous_to_event
Anthropocene
[ "multi-temporal InSAR surface displacement velocity fields and continuous GNSS station networks", "broadband seismic tomography, receiver-function conversions, and shear-wave splitting measurements" ]
[ "volatile exsolution kinetics and overpressure thresholds triggering dike propagation" ]
[ "multiphase magma viscosity $\\eta(\\phi_c, C_{\\mathrm{H2O}}, T) = \\eta_{\\mathrm{melt}}(C_{\\mathrm{H2O}}, T) (1 - \\phi_c / \\phi_m)^{-B \\phi_m}$ and Deborah fragmentation criterion $\\mathrm{De} = \\eta \\dot{\\gamma} / G_\\infty \\ge 10^{-2}$", "conduit momentum-continuity balance $\\rho_m u \\partial_z u ...
Formulated in Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing (ERUPT) (2017, GC-1); corroborated across Scudero et al. (2019) and Girona et al. (2015). Remains open due to coupled mafic magma recharge, volatile exsolution buoyancy, and conduit shear heating and magma viscosity, conduit geometry, and...
Co-located observations of multi-temporal InSAR surface displacement velocity fields and continuous GNSS station networks and broadband seismic tomography, receiver-function conversions, and shear-wave splitting measurements across Active Arc, Rift, and Hotspot Volcanic Systems coupled with process-resolving models of ...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,017
Committee on Improving Understanding of Volcanic Eruptions, M. Manga (Chair)
2026-10-16T00:00:00
[ "UEARTH-001545", "UEARTH-001600", "UEARTH-000367" ]
[ "10.17226/24650", "10.1038/s41598-019-40563-0", "10.1038/srep18212", "10.25740/hy589fc7561" ]
[ "Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing (ERUPT) (2017), Grand Challenges in Volcano Science (GC-1), DOI:10.17226/24650", "Scudero et al. (2019), Scientific Reports, DOI:10.1038/s41598-019-40563-0", "Girona et al. (2015), Scientific reports, DOI:10.1038/srep18212", "E. E. Brodsky, ...
UEARTH-000022
22
Up-Dip Rupture Propagation and Tsunamigenesis on Shallow Subduction Megathrusts (SZ4D FEC)
Under what frictional, wedge-compliance, and fluid-overpressure conditions does a subduction megathrust earthquake propagate through the nominally velocity-strengthening shallow trench wedge to generate an outsized tsunami?
Why do some subduction earthquakes break all the way to the seafloor trench and trigger massive tsunamis when shallow sediments should resist seismic slip?
In the shallowest $0\text{--}15\,\mathrm{km}$ of subduction interfaces, how do dynamic weakening (thermal pressurization of low-permeability clay-rich décollements), inelastic outer-wedge splay faulting, and inelastic seafloor uplift govern tsunami excitation during $M_w \ge 8.5$ megathrust ruptures?
earthquakes_volcanoes_tsunamis_geohazards
2
Earthquakes, Volcanoes, Tsunamis, and Geohazards
tsunami_seafloor_displacement
3
[ "mechanism", "hazard_generation" ]
[ "seafloor", "coast" ]
[ "seawater", "marine_sediment" ]
[ "fault_rupture_and_slip", "coastal_and_estuarine_morphodynamics" ]
ocean_basin_or_gyre
Tsunamigenic Subduction Trenches and Coastal Margins
instantaneous_to_event
Holocene
[ "DART deep-ocean bottom pressure records, cabled seafloor observatories, and tide-gauge waveforms", "post-tsunami coastal runup surveys, boulder transport limits, and paleotsunami sand sheets" ]
[ "shallow trench-wedge splay-fault slip partitioning and tsunami-earthquake dispersive wave amplification" ]
[ "dispersive Boussinesq shallow-water wave propagation $\\partial_t \\eta + \\nabla \\cdot [(h + \\eta)\\mathbf{u}] = \\partial_t \\zeta_{\\mathrm{seafloor}}$ with phase speed $c = \\sqrt{g h (1 - k^2 h^2 / 3)}$", "Okada elastic/inelastic coseismic vertical seafloor uplift $u_z(x,y)$ amplifying shallow trench slip...
Formulated in SZ4D Implementation Plan: Subduction Zones in Four Dimensions (2022, FEC-Q2); corroborated across Yanagisawa et al. (2016) and Qiu et al. (2019). Remains open due to coupled coseismic seafloor vertical displacement and submarine mass-failure acceleration and continental shelf bathymetry, coastal topograph...
Co-located observations of DART deep-ocean bottom pressure records, cabled seafloor observatories, and tide-gauge waveforms and post-tsunami coastal runup surveys, boulder transport limits, and paleotsunami sand sheets across Tsunamigenic Subduction Trenches and Coastal Margins coupled with process-resolving models of ...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,022
E. E. Brodsky, T. A. Plank
2026-10-16T00:00:00
[ "UEARTH-002506", "UEARTH-001816", "UEARTH-000479" ]
[ "10.25740/hy589fc7561", "10.1002/2015jb012617", "10.5194/nhess-19-1565-2019", "10.25740/hy589fc7561" ]
[ "SZ4D Implementation Plan: Subduction Zones in Four Dimensions (2022), Faulting and Earthquake Cycles (FEC-Q2), DOI:10.25740/hy589fc7561", "Yanagisawa et al. (2016), Journal of Geophysical Research Solid Earth, DOI:10.1002/2015jb012617", "Qiu et al. (2019), Natural hazards and earth system sciences, DOI:10.5194...
UEARTH-000023
23
Deep Earth Cycling and Partitioning of Critical Elements and Volatiles (Earth in Time Q3)
What thermodynamic, redox, and mineral-fluid partitioning mechanisms govern the distribution, deep-mantle recycling, and crustal concentration of critical elements and volatiles (H, C, N, S, halogens) through Earth history?
How do water, carbon, sulfur, and critical metals cycle between Earth's surface and deep interior to form concentrated mineral deposits?
Across subduction dehydration, mantle-wedge metasomatism, and transcrustal magmatic-hydrothermal differentiation, how do oxygen fugacity ($f\mathrm{O}_2$), sulfur speciation ($\mathrm{S}^{2-}/\mathrm{S}^{6+}$), and supercritical fluid-melt partition coefficients control the deep volatile budget and porphyry/epithermal ...
geochemistry_mineralogy_petrology_earth_materials
3
Geochemistry, Mineralogy, Petrology, and Earth Materials
hydrothermal_ore_deposits_metallogeny
1
[ "mechanism", "budget" ]
[ "hydrothermal_system", "continental_crust" ]
[ "hydrothermal_fluid", "crystalline_rock" ]
[ "redox_transformation", "magma_generation_and_ascent" ]
core_to_outcrop
Magmatic–Hydrothermal and Submarine Metallogenic Belts
multi_million_year_tectonic
Cenozoic
[ "fluid-inclusion microthermometry, Raman spectroscopy, and LA-ICP-MS single-inclusion metal assays", "in-situ sulfur, oxygen, and copper/iron/zinc stable isotope zoning across ore paragenetic stages" ]
[ "magmatic-hydrothermal fluid flux budgets and structural permeability focusing mechanisms" ]
[ "fluid-melt metal partitioning $D_M^{\\mathrm{fluid/melt}}(P, T, X_{\\mathrm{Cl}}, X_{\\mathrm{S}}, f\\mathrm{O}_2)$ and Helgeson-Kirkham-Flowers log $K(T, \\rho_w)$", "chalcophile sulfide-silicate partitioning $D_{\\mathrm{Cu,Au}}^{\\mathrm{sulf/sil}} \\sim 10^3\\text{--}10^5$ vs. volatile saturation timing" ]
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 3); corroborated across Wang et al. (2026) and Liang et al. (2024). Remains open due to coupled magmatic fluid exsolution, decompression boiling, and fluid-rock redox reactions and host-rock buffering capacity, fault-fracture network...
Co-located observations of fluid-inclusion microthermometry, Raman spectroscopy, and LA-ICP-MS single-inclusion metal assays and in-situ sulfur, oxygen, and copper/iron/zinc stable isotope zoning across ore paragenetic stages across Magmatic–Hydrothermal and Submarine Metallogenic Belts coupled with process-resolving m...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
medium
3
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-002583", "UEARTH-002800", "UEARTH-003767" ]
[ "10.17226/25761", "10.1038/s41467-026-74619-3", "10.2138/am-2023-9217", "10.6075/J0W66J9H" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Priority Questions (Question 3), DOI:10.17226/25761", "Wang et al. (2026), Nature communications, DOI:10.1038/s41467-026-74619-3", "Liang et al. (2024), American Mineralogist, DOI:10.2138/am-2023-9217", "A. A. P. Koppers and R. Coggon (Eds.) (2...
UEARTH-000024
24
Serpentinization Kinetics and Abiotic Hydrogen-Methane Fluxes in Ultramafic Oceanic Lithosphere
What mineralogical, temperature, and fluid-pathway controls govern the rate of peridotite serpentinization, magnetite catalysis, and abiotic $\mathrm{H}_2$ and $\mathrm{CH}_4$ production in slow-spreading oceanic lithosphere and forearc mantles?
What controls the rate at which seawater reacts with mantle rocks to produce hydrogen and abiotic methane beneath the seafloor?
At $50\text{--}400\,^\circ\mathrm{C}$ inabyssal peridotites and subduction forearcs, how does reaction-induced cracking versus pore-space clogging interact with iron partitioning between brucite, serpentine, and magnetite to regulate $\mathrm{H}_2$ generation and Fischer-Tropsch-type carbon reduction?
geochemistry_mineralogy_petrology_earth_materials
3
Geochemistry, Mineralogy, Petrology, and Earth Materials
igneous_petrology_magmatic_differentiation
3
[ "mechanism", "rate" ]
[ "magma_reservoir", "continental_crust" ]
[ "magma_or_melt", "crystalline_rock" ]
[ "magma_generation_and_ascent", "metamorphic_transformation" ]
core_to_outcrop
Crustal and Upper-Mantle Magmatic Provinces
multi_million_year_tectonic
Cenozoic
[ "electron microprobe and LA-ICP-MS mineral/melt-inclusion major and trace element zoning", "piston-cylinder and multi-anvil phase-equilibrium experiments and radiogenic Sr-Nd-Hf isotopes" ]
[ "degree of partial melting, crustal assimilation vs. fractional crystallization (AFC) mass balance" ]
[ "open-system assimilation-fractional crystallization (AFC) $dC_m/dF = [r/(r-1)] C_a / F - D_{\\mathrm{bulk}} C_m / F$ and oxygen fugacity $\\Delta \\mathrm{FMQ}$", "McKenzie compaction length $\\delta_c = \\sqrt{k_\\phi (\\zeta + 4\\eta/3) / \\mu_f}$ governing melt extraction from crystal mush" ]
Formulated in Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework (2020, SO-1); corroborated across Huang et al. (2017) and Zhang et al. (2023). Remains open due to coupled decompression melting, mantle heat flux, and flux melting by slab-derived volatiles and source rock fertility, oxygen fugacity (fO...
Co-located observations of electron microprobe and LA-ICP-MS mineral/melt-inclusion major and trace element zoning and piston-cylinder and multi-anvil phase-equilibrium experiments and radiogenic Sr-Nd-Hf isotopes across Crustal and Upper-Mantle Magmatic Provinces coupled with process-resolving models of magma generati...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,020
A. A. P. Koppers, R. Coggon
2026-10-16T00:00:00
[ "UEARTH-002611", "UEARTH-002579", "UEARTH-000450" ]
[ "10.6075/J0W66J9H", "10.1016/j.gsf.2017.01.001", "10.1093/nsr/nwac207", "10.6075/J0W66J9H" ]
[ "Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework (2020), Habitability and Life on Earth (SO-1), DOI:10.6075/J0W66J9H", "Huang et al. (2017), Geoscience Frontiers, DOI:10.1016/j.gsf.2017.01.001", "Zhang et al. (2023), National science review, DOI:10.1093/nsr/nwac207", "A. A. P. Koppers and...
UEARTH-000025
25
Equable High-Latitude Warmth and Meridional Temperature Gradients in Hothouse Climates
What radiative, cloud-microphysical, or ocean-atmosphere heat-transport mechanisms sustained ice-free polar warmth and reduced meridional sea-surface temperature gradients during Early Eocene and Cretaceous hothouse climates?
How did Earth's poles stay warm enough for crocodiles and palm trees during ancient greenhouse climates without overheating the tropics?
During the Early Eocene Climatic Optimum ($\sim 53\text{--}49\,\mathrm{Ma}$, $\mathrm{CO}_2 \sim 1,000\text{--}1,600\,\mathrm{ppm}$), does reconciling clumped-isotope ($\Delta_{47}$), $\mathrm{TEX}_{86}$, and $\delta^{18}\mathrm{O}$ SST proxies with Earth system models require optically thinner polar stratocumulus clou...
geologic_time_paleoclimate_stratigraphy_earth_history
4
Geologic Time, Paleoclimate, Stratigraphy, and Earth History
greenhouse_hyperthermals_cenozoic_mesozoic
8
[ "mechanism", "transport" ]
[ "sedimentary_stratigraphic_archive", "marine_sediment" ]
[ "marine_sediment", "sedimentary_rock" ]
[ "carbon_cycle_and_biogeochemical_cycling", "radiative_transfer_and_energy_balance" ]
planetary_global
Global and Representative Regional Observatories
multi_million_year_tectonic
Mesozoic
[ "IODP deep-sea core carbon-isotope excursions (CIEs), clumped-isotope (Delta47) paleothermometry, and boron-isotope pCO2", "cyclo- and magnetostratigraphic age models and osmium/strontium weathering-proxy records" ]
[ "silicate-weathering and organic-carbon burial negative feedback timescales following carbon-cycle perturbations" ]
[ "carbon-cycle isotope mass balance $\\Delta \\delta^{13}\\mathrm{C}_{\\mathrm{ex}} = M_{\\mathrm{emit}} (\\delta^{13}\\mathrm{C}_{\\mathrm{src}} - \\delta^{13}\\mathrm{C}_0) / (M_0 + M_{\\mathrm{emit}})$ and Walker silicate weathering $F_{\\mathrm{sil}} \\propto p\\mathrm{CO}_2^\\beta \\exp(\\Delta T / T_e)$", "E...
Formulated in Past climates inform our future (2020, Section 2); corroborated across Harper et al. (2024) and Hovikoski et al. (2021). Remains open due to coupled Large Igneous Province (LIP) volcanic degassing, methane hydrate dissociation, and gateway tectonics and paleogeographic continental configuration, ocean gat...
Co-located observations of IODP deep-sea core carbon-isotope excursions (CIEs), clumped-isotope (Delta47) paleothermometry, and boron-isotope pCO2 and cyclo- and magnetostratigraphic age models and osmium/strontium weathering-proxy records across Global and Representative Regional Observatories coupled with process-res...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,020
Jessica E. Tierney, Christopher J. Poulsen
2026-10-16T00:00:00
[ "UEARTH-000109", "UEARTH-003931", "UEARTH-007923" ]
[ "10.1126/science.aay3701", "10.1073/pnas.2318779121", "10.1038/s43247-021-00249-w", "10.1126/science.aay3701" ]
[ "Past climates inform our future (2020), Hothouse Climates (Section 2), DOI:10.1126/science.aay3701", "Harper et al. (2024), Proceedings of the National Academy of Sciences of the United States of America, DOI:10.1073/pnas.2318779121", "Hovikoski et al. (2021), Communications Earth & Environment, DOI:10.1038/s4...
UEARTH-000026
26
Biogeochemical Controls on the Proterozoic Atmospheric Oxygen Stasis and Neoproterozoic Oxygenation
What coupled phosphorus-iron-sulfur feedbacks maintained atmospheric oxygen at low levels ($0.1\text{--}10\%$ PAL) throughout the mid-Proterozoic 'Boring Billion', and what tectonic or biological trigger drove the Neoproterozoic Oxygenation Event?
Why did Earth's atmospheric oxygen stay low for over a billion years after the first oxygenation event before rising enough to support animal life?
Between $1.8\,\mathrm{Ga}$ and $0.8\,\mathrm{Ga}$, how did ferruginous/euxinic deep-ocean phosphorus scavenging, terrestrial oxidative weathering efficiency, and organic carbon burial fractions ($f_{\mathrm{org}}$ constrained by $\delta^{13}\mathrm{C}$ and $\delta^{53}\mathrm{Cr}$) stabilize low atmospheric $p\mathrm{O...
geologic_time_paleoclimate_stratigraphy_earth_history
4
Geologic Time, Paleoclimate, Stratigraphy, and Earth History
precambrian_oxygenation_early_earth
8
[ "mechanism", "reconstruction" ]
[ "sedimentary_stratigraphic_archive", "atmosphere" ]
[ "sedimentary_rock", "marine_sediment" ]
[ "redox_transformation", "carbon_cycle_and_biogeochemical_cycling" ]
planetary_global
Global and Representative Regional Observatories
billion_year_planetary
Precambrian
[ "mass-independent sulfur isotopes (Delta33S), iron speciation, and Ce/Mo/U/Cr redox-sensitive trace-metal shales", "carbonate-associated sulfate and detrital redox-sensitive mineral assemblages" ]
[ "stepwise oxygenation of Earth's atmosphere and deep oceans across the GOE and NOE" ]
[ "global redox-carbon burial balance $F_{\\mathrm{O2,source}} = F_{\\mathrm{total\\,C}} \\cdot f_{\\mathrm{org}}(\\delta^{13}\\mathrm{C}) + F_{\\mathrm{pyr}} - F_{\\mathrm{volc\\,red}} - F_{\\mathrm{ox\\,weath}}(p\\mathrm{O}_2)$", "planetary radiative balance $(S_\\odot(t)/4)(1 - A_p) = \\mathrm{OLR}(T_s, p\\mathr...
Formulated in The rise of oxygen in Earth's early ocean and atmosphere (2014, Section 3); corroborated across Hou et al. (2025) and Krause et al. (2022). Remains open due to coupled oxygenic photosynthesis evolution, mantle reducer outgassing decline, and Snowball Earth glaciations and continental emergence area, marin...
Co-located observations of mass-independent sulfur isotopes (Delta33S), iron speciation, and Ce/Mo/U/Cr redox-sensitive trace-metal shales and carbonate-associated sulfate and detrital redox-sensitive mineral assemblages across Global and Representative Regional Observatories coupled with process-resolving models of re...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
hard
4
2,014
Timothy W. Lyons, Christopher T. Reinhard
2026-10-16T00:00:00
[ "UEARTH-004937", "UEARTH-004964", "UEARTH-012519" ]
[ "10.1038/nature13068", "10.1029/2025jg008835", "10.1126/sciadv.abm8191", "10.1126/science.aay3701" ]
[ "The rise of oxygen in Earth's early ocean and atmosphere (2014), Proterozoic Redox Evolution (Section 3), DOI:10.1038/nature13068", "Hou et al. (2025), Journal of Geophysical Research Biogeosciences, DOI:10.1029/2025jg008835", "Krause et al. (2022), Science Advances, DOI:10.1126/sciadv.abm8191", "J. E. Tiern...
UEARTH-000027
27
Reciprocal Coupling Between Tectonic Uplift, Erosion, and Climate Evolution (Earth in Time Q5)
Do Cenozoic mountain building, monsoon intensification, and glacial valley incision drive global silicate weathering cooling, or does late-Cenozoic climatic cooling and precipitation variability primarily accelerate mountain erosion?
Do rising mountain ranges cool Earth's climate by eroding rock, or does a cooling, stormier climate speed up the erosion of mountains?
Over $10^5\text{--}10^7\,\mathrm{yr}$ timescales in active orogens (Himalaya-Tibet, Andes, Southern Alps), how can detrital thermochronology, cosmogenic nuclide ($^{10}\mathrm{Be}$, $^{26}\mathrm{Al}$) denudation rates, and lithium/osmium marine isotope records resolve the causal direction between tectonic rock uplift,...
geomorphology_sediments_surface_processes
5
Geomorphology, Sediments, and Surface Processes
tectonic_geomorphology_orogenic_erosion
1
[ "mechanism", "reconstruction" ]
[ "orogen", "river" ]
[ "crystalline_rock", "fluvial_or_coastal_sediment" ]
[ "physical_erosion_and_denudation", "crustal_deformation" ]
tectonic_plate_or_orogen
Himalaya–Tibetan Plateau and Central Asian Orogenic System
millennial_to_orbital
Cenozoic
[ "in-situ terrestrial cosmogenic nuclide (10Be, 26Al) surface exposure and denudation inventories", "catchment-wide cosmogenic 10Be denudation rates, low-temperature apatite (U-Th)/He ages, and channel steepness (ksn)" ]
[ "transient landscape response to drainage reorganization and glacial-fluvial erosion switching" ]
[ "stream-power incision and hillslope diffusion $\\partial_t z = U(x,y) - K A^m |\\nabla z|^n + D \\nabla^2 z$ and integral $\\chi = \\int_{x_b}^x (A_0/A(x'))^{m/n} dx'$", "cosmogenic $^{10}\\mathrm{Be}$ steady-state denudation $N_{10} = P_0 / (\\lambda_{10} + \\rho_r \\varepsilon / \\Lambda_{\\mathrm{atten}})$" ]
Formulated in A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020, Question 5); corroborated across Kim et al. (2022) and Wang et al. (2020). Remains open due to coupled tectonic rock uplift, orographic precipitation focus, and Quaternary glaciation cycles and bedrock lithological erodibility, fracture spaci...
Co-located observations of in-situ terrestrial cosmogenic nuclide (10Be, 26Al) surface exposure and denudation inventories and catchment-wide cosmogenic 10Be denudation rates, low-temperature apatite (U-Th)/He ages, and channel steepness (ksn) across Himalaya–Tibetan Plateau and Central Asian Orogenic System coupled wi...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,020
National Academies Committee on Catalyzing Opportunities for Research in the Earth Sciences (CORES)
2026-10-16T00:00:00
[ "UEARTH-006035", "UEARTH-005957", "UEARTH-002152" ]
[ "10.17226/25761", "10.1080/04353676.2022.2121998", "10.2113/2020/7866972", "10.1038/s43017-021-00253-w" ]
[ "A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020), Priority Questions (Question 5), DOI:10.17226/25761", "Kim et al. (2022), Geografiska Annaler Series A Physical Geography, DOI:10.1080/04353676.2022.2121998", "Wang et al. (2020), Lithosphere, DOI:10.2113/2020/7866972", "J. Syvitski, J. R. Ánge...
UEARTH-000028
28
Source-to-Sink Sediment Buffering and Lag Times Across Alluvial Floodplains
How do alluvial floodplain storage, channel avulsion frequency, and grain-size fining buffer and delay the transmission of upland tectonic and anthropogenic erosion signals to continental margins?
How long do rivers store eroded sediment on floodplains before delivering it to deltas and the ocean, and how does this hide upstream erosion changes?
In large source-to-sink river systems ($L > 10^2\text{--}10^3\,\mathrm{km}$), what controls the nonlinear diffusive mass-transfer timescale ($\tau_{\mathrm{eq}} \sim L^2 / \kappa_s$) and how does dam trapping plus floodplain exchange mask hydroclimatic sediment pulses?
geomorphology_sediments_surface_processes
5
Geomorphology, Sediments, and Surface Processes
fluvial_channel_sediment_transport
7
[ "mechanism", "budget" ]
[ "river", "floodplain" ]
[ "fluvial_or_coastal_sediment", "freshwater_surface" ]
[ "sediment_transport_and_deposition", "physical_erosion_and_denudation" ]
reach
Global and Representative Regional Observatories
interannual_to_decadal
Holocene
[ "acoustic Doppler bedload/suspended-flux profiles, repeat airborne LiDAR/bathymetric DEMs, and grain-size distributions", "in-situ cosmogenic nuclide (10Be/26Al) catchment erosion rates and fallout radionuclide (137Cs/210Pb) budgets" ]
[ "nonlinear bedload transport thresholds, channel-width adjustment laws, and avulsion return periods" ]
[ "Shields dimensionless bed shear stress $\\tau^* = \\tau_b / [(\\rho_s - \\rho_w) g D_{50}] \\ge \\tau^*_c$ and Exner conservation $(1 - \\lambda_p) \\partial_t \\eta = -\\nabla \\cdot \\mathbf{q}_b$", "Rouse suspended sediment concentration profile $C(z)/C_a = [(h-z)/z \\cdot a/(h-a)]^{\\mathrm{Ro}}$ where $\\ma...
Formulated in Earth's sediment cycle during the Anthropocene (2022, Section 4); corroborated across D’Arcy et al. (2016) and Liu et al. (2025). Remains open due to coupled flood hydrograph flashiness, tectonic base-level fall, and upstream sediment supply pulses and bed grain-size armoring, riparian bank cohesion, and ...
Co-located observations of acoustic Doppler bedload/suspended-flux profiles, repeat airborne LiDAR/bathymetric DEMs, and grain-size distributions and in-situ cosmogenic nuclide (10Be/26Al) catchment erosion rates and fallout radionuclide (137Cs/210Pb) budgets across Global and Representative Regional Observatories coup...
open
scale_dependent_disagreement
OPEN-VERIFIED
true
medium
3
2,022
Jaia Syvitski, Juan Restrepo Ángel
2026-10-16T00:00:00
[ "UEARTH-005349", "UEARTH-005139", "UEARTH-013816" ]
[ "10.1038/s43017-021-00253-w", "10.1111/sed.12308", "10.1038/s41598-025-11451-7", "10.1038/s43017-021-00253-w" ]
[ "Earth's sediment cycle during the Anthropocene (2022), Anthropocene Sediment Cycle (Section 4), DOI:10.1038/s43017-021-00253-w", "D’Arcy et al. (2016), Sedimentology, DOI:10.1111/sed.12308", "Liu et al. (2025), Scientific Reports, DOI:10.1038/s41598-025-11451-7", "J. Syvitski, J. R. Ángel, Y. Saito et al. (2...
UEARTH-000029
29
Physical Mechanisms of Convective Self-Aggregation in the Tropical Atmosphere (WCRP Q1)
What radiative, surface-flux, and cold-pool moisture feedbacks control convective self-aggregation in the real tropical atmosphere, and how does aggregation modulate tropical tropospheric humidity and outgoing longwave radiation?
What causes tropical thunderstorms to cluster together into organized systems, and how does that clustering dry out the surrounding atmosphere?
Across mesoscale-to-planetary tropical domains, how do longwave radiative cooling contrasts between dry subsiding regions and moist anvil clouds interact with boundary-layer cold pools and sea-surface temperature gradients to drive convective organization (governed by column moist static energy budget $\langle \partial...
atmosphere_weather_atmospheric_chemistry
6
Atmosphere, Weather, and Atmospheric Chemistry
convective_storms_tropical_cyclones_monsoon
4
[ "mechanism", "budget" ]
[ "troposphere", "boundary_layer" ]
[ "tropospheric_air", "precipitation" ]
[ "atmospheric_convection_and_circulation", "cloud_microphysics_and_aerosol_interaction" ]
regional_synoptic
Global and Representative Regional Observatories
diurnal_to_synoptic
Anthropocene
[ "phased-array and dual-polarization weather radar, dropsonde wind/thermodynamic profiles, and geostationary IR/lightning imagers", "cloud-resolving (km-scale) ensemble hindcasts and airborne Doppler radar vorticity retrievals" ]
[ "stochastic boundary-layer trigger mechanisms for deep moist convection initiation over complex terrain" ]
[ "convective available potential energy $\\mathrm{CAPE} = \\int_{\\mathrm{LFC}}^{\\mathrm{EL}} g (\\theta_{v,\\mathrm{parcel}} - \\theta_{v,\\mathrm{env}})/\\theta_{v,\\mathrm{env}} dz$ and entraining plume mass flux $\\partial_z \\ln M = \\varepsilon - \\delta$", "column moist static energy budget $\\langle \\par...
Formulated in Clouds, circulation and climate sensitivity (2015, Box 1 Question 1); corroborated across Muller et al. (2018) and Lutsko et al. (2018). Remains open due to coupled convective available potential energy (CAPE), sea-surface enthalpy fluxes, and vertical wind shear and mid-tropospheric dry-air entrainment, ...
Co-located observations of phased-array and dual-polarization weather radar, dropsonde wind/thermodynamic profiles, and geostationary IR/lightning imagers and cloud-resolving (km-scale) ensemble hindcasts and airborne Doppler radar vorticity retrievals across Global and Representative Regional Observatories coupled wit...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,015
S. Bony, B. Stevens
2026-10-16T00:00:00
[ "UEARTH-000190", "UEARTH-006337", "UEARTH-000218" ]
[ "10.1038/ngeo2398", "10.1073/pnas.1719967115", "10.1029/2018ms001482", "10.1029/2019RG000678" ]
[ "Clouds, circulation and climate sensitivity (2015), Guiding Questions (Box 1 Question 1), DOI:10.1038/ngeo2398", "Muller et al. (2018), Proceedings of the National Academy of Sciences of the United States of America, DOI:10.1073/pnas.1719967115", "Lutsko et al. (2018), Journal of Advances in Modeling Earth Sys...
UEARTH-000030
30
Aerosol-Cloud Microphysical Buffering and Radiative Forcing in Mixed-Phase Clouds
How do ice-nucleating particles, secondary ice production (Hallett-Mossop, droplet fragmentation), and Wegener-Bergeron-Findeisen phase partitioning control the liquid-water path and albedo of high-latitude and mid-latitude mixed-phase clouds?
What controls the balance of supercooled liquid water and ice crystals in clouds between 0°C and -38°C, and how does pollution change their brightness?
In supercooled mixed-phase clouds ($235\,\mathrm{K} < T < 273\,\mathrm{K}$), what microphysical rates of heterogeneous immersion freezing, rime splintering, and turbulent updraft supersaturation govern cloud glaciation timescales and cloud-phase radiative feedback?
atmosphere_weather_atmospheric_chemistry
6
Atmosphere, Weather, and Atmospheric Chemistry
cloud_microphysics_aerosol_ccn_in
4
[ "mechanism", "budget" ]
[ "troposphere", "boundary_layer" ]
[ "aerosol_or_cloud_hydrometeor", "cloud_water" ]
[ "cloud_microphysics_and_aerosol_interaction", "radiative_transfer_and_energy_balance" ]
regional_synoptic
Global and Representative Regional Observatories
diurnal_to_synoptic
Holocene
[ "aircraft in-situ cloud-droplet/ice-crystal optical array probes and dual-polarization Doppler cloud radar/lidar", "continuous-flow diffusion chamber ice-nucleating particle (INP) spectra and CCN supersaturation counters" ]
[ "secondary ice production (SIP) multiplication rates and supercooled liquid-to-ice phase partitioning" ]
[ "Köhler droplet activation supersaturation $S(r) = 1 + A/r - \\kappa_{\\mathrm{hyg}} r_{\\mathrm{dry}}^3 / r^3$ and Wegener-Bergeron-Findeisen relaxation $\\tau_{\\mathrm{phase}}^{-1} = 4\\pi D_v (N_w r_w + N_i C_i)$", "autoconversion-accretion warm-rain balance $\\partial_t q_r = k_{\\mathrm{auto}} q_c^{\\alpha_...
Formulated in Climate Change 2021: The Physical Science Basis (IPCC AR6 WGI) (2021, Chapter 7 Section 7.4); corroborated across Bikkina et al. (2026) and Frostenberg et al. (2026). Remains open due to coupled updraft supersaturation fluctuations, radiative cloud-top cooling, and aerosol loading perturbations and lower-...
Co-located observations of aircraft in-situ cloud-droplet/ice-crystal optical array probes and dual-polarization Doppler cloud radar/lidar and continuous-flow diffusion chamber ice-nucleating particle (INP) spectra and CCN supersaturation counters across Global and Representative Regional Observatories coupled with pro...
open
model_structural_uncertainty
OPEN-VERIFIED
true
hard
4
2,021
IPCC Working Group I
2026-10-16T00:00:00
[ "UEARTH-000205", "UEARTH-006523", "UEARTH-007812" ]
[ "10.1017/9781009157896", "10.1021/acsestair.5c00471", "10.1038/s41612-026-01342-7", "10.1029/2019RG000678" ]
[ "Climate Change 2021: The Physical Science Basis (IPCC AR6 WGI) (2021), Clouds and Aerosols (Chapter 7 Section 7.4), DOI:10.1017/9781009157896", "Bikkina et al. (2026), ACS ES&T Air, DOI:10.1021/acsestair.5c00471", "Frostenberg et al. (2026), NPJ climate and atmospheric science, DOI:10.1038/s41612-026-01342-7",...
UEARTH-000031
31
Subtropical Marine Low-Cloud Feedback and the Upper Bound of Equilibrium Climate Sensitivity
How do boundary-layer decoupling, cloud-top radiative cooling, and entrainment drying govern the response of subtropical marine stratocumulus and trade-wind cumulus decks to surface warming, and what sets the upper bound of Equilibrium Climate Sensitivity?
How strongly will low ocean clouds thin as the planet warms, and how much extra warming will that cloud loss cause?
In eastern subtropical ocean basins, what quantitative balance between latent heat flux drying (moisture-gradient entrainment) and cloud-top longwave cooling reduction controls low-cloud optical depth and fractional coverage feedback ($\lambda_{\mathrm{cloud}}$ in $\mathrm{W\,m^{-2}\,K^{-1}}$)?
climate_dynamics_feedbacks_predictability_extremes
7
Climate Dynamics, Feedbacks, Predictability, and Extremes
climate_sensitivity_cloud_radiative_feedbacks
4
[ "mechanism", "feedback" ]
[ "atmosphere", "ocean" ]
[ "tropospheric_air", "aerosol_or_cloud_hydrometeor" ]
[ "radiative_transfer_and_energy_balance", "cloud_microphysics_and_aerosol_interaction" ]
planetary_global
Global and Representative Regional Observatories
multidecadal
Anthropocene
[ "CERES/ERBE top-of-atmosphere radiative energy budget time series and Argo global ocean heat uptake", "A-Train active cloud radar/lidar radiative kernel decompositions and CMIP6 multi-model ensembles" ]
[ "state dependence of tropical anvil-cloud area and extratropical mixed-phase optical-depth feedbacks" ]
[ "radiative feedback decomposition $N(t) = \\Delta F(t) + (\\lambda_P + \\lambda_{\\mathrm{WV+LR}} + \\lambda_{\\mathrm{alb}} + \\lambda_{\\mathrm{cld}} + \\Delta \\lambda_{\\mathrm{pattern}}(t)) \\Delta T_s(t)$", "Equilibrium Climate Sensitivity $\\mathrm{ECS} = -F_{2\\times\\mathrm{CO2}} / \\lambda_{\\mathrm{net...
Formulated in An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence (2020, Section 3.2); corroborated across McGraw et al. (2025) and Hirota et al. (2021). Remains partially solved due to coupled anthropogenic greenhouse-gas radiative forcing and spatially heterogeneous aerosol forcing and tropi...
Co-located observations of CERES/ERBE top-of-atmosphere radiative energy budget time series and Argo global ocean heat uptake and A-Train active cloud radar/lidar radiative kernel decompositions and CMIP6 multi-model ensembles across Global and Representative Regional Observatories coupled with process-resolving models...
partially_solved
mechanism_known_magnitude_uncertain
PARTIAL-PROGRESS
true
hard
4
2,020
S. C. Sherwood, M. J. Webb
2026-10-16T00:00:00
[ "UEARTH-007982", "UEARTH-000207", "UEARTH-006317" ]
[ "10.1029/2019RG000678", "10.1029/2024gl112368", "10.1088/1748-9326/abfb9e", "10.1017/9781009157896" ]
[ "An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence (2020), Cloud Feedbacks (Section 3.2), DOI:10.1029/2019RG000678", "McGraw et al. (2025), Geophysical Research Letters, DOI:10.1029/2024gl112368", "Hirota et al. (2021), Environmental Research Letters, DOI:10.1088/1748-9326/abfb9e", ...
UEARTH-000032
32
Stability Thresholds and Early-Warning Observables for Atlantic Meridional Overturning Circulation (AMOC)
Does the Atlantic Meridional Overturning Circulation (AMOC) possess a salt-advection bistability threshold reachable under 21st-century Greenland meltwater and precipitation forcing, and can freshwater transport diagnostics ($F_{\mathrm{ovS}}$) distinguish approaching criticality from multidecadal internal variability?
Could Atlantic ocean currents cross a tipping point and shut down due to freshwater melting from Greenland, and can ocean measurements warn us in advance?
At $34^\circ\mathrm{S}$ and $26.5^\circ\mathrm{N}$ (RAPID-MOCHA), is the net overturning freshwater import $F_{\mathrm{ov}}$ robustly negative, and how do wind-driven gyre salt transport and Nordic Seas overflow mixing modify the Stommel salt-advection bifurcation boundary?
climate_dynamics_feedbacks_predictability_extremes
7
Climate Dynamics, Feedbacks, Predictability, and Extremes
global_carbon_climate_tipping_feedbacks
4
[ "mechanism", "threshold" ]
[ "atmosphere", "biosphere" ]
[ "tropospheric_air", "biota" ]
[ "carbon_cycle_and_biogeochemical_cycling", "radiative_transfer_and_energy_balance" ]
planetary_global
Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain
centennial_to_millennial
Quaternary
[ "global atmospheric CO2/CH4/N2O flask networks, satellite column XCO2/XCH4 (OCO-2/GOSAT), and ocean pCO2", "coupled C4MIP Earth System Model simulations and paleoclimate abrupt-transition records" ]
[ "critical warming thresholds and cascading interactions among Earth-system tipping elements" ]
[ "Arora carbon-climate feedback framework $\\Delta C_L + \\Delta C_O = (\\beta_L + \\beta_O) \\Delta C_A + (\\gamma_L + \\gamma_O) \\Delta T_s$", "early-warning critical slowing down autocorrelation $\\mathrm{AR}(1) = \\exp(-\\lambda_{\\mathrm{rest}} \\Delta t) \\to 1$ and variance $\\sigma_x^2 = \\sigma_\\eta^2 /...
Formulated in Exceeding 1.5°C global warming could trigger multiple climate tipping points (2022, Table 1 AMOC); corroborated across Shin et al. (2024) and Sun et al. (2020). Remains open due to coupled cumulative anthropogenic carbon emissions and high-latitude/tropical warming amplification and ocean carbonate buffer...
Co-located observations of global atmospheric CO2/CH4/N2O flask networks, satellite column XCO2/XCH4 (OCO-2/GOSAT), and ocean pCO2 and coupled C4MIP Earth System Model simulations and paleoclimate abrupt-transition records across Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain coupled with process-resolv...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,022
David I. Armstrong McKay, Arie Staal
2026-10-16T00:00:00
[ "UEARTH-009448", "UEARTH-009177", "UEARTH-009850" ]
[ "10.1126/science.abn7950", "10.1029/2024gl108272", "10.1002/joc.6695", "10.1017/9781009157896" ]
[ "Exceeding 1.5°C global warming could trigger multiple climate tipping points (2022), Ocean Circulation Tipping Elements (Table 1 AMOC), DOI:10.1126/science.abn7950", "Shin et al. (2024), Geophysical Research Letters, DOI:10.1029/2024gl108272", "Sun et al. (2020), International Journal of Climatology, DOI:10.10...
UEARTH-000033
33
Marine Ice Sheet and Marine Ice Cliff Instability Thresholds in West Antarctica
What basal sliding law, sub-shelf melt distribution, and hydrofracture-driven ice-cliff structural failure criteria govern the rate of grounding-line retreat in retrograde West Antarctic basins such as Thwaites and Pine Island Glaciers?
How fast will West Antarctic glaciers retreat once warm ocean water melts their floating ice shelves, and will towering ice cliffs collapse rapidly?
Along retrograde bedrock slopes in the Amundsen Sea Embayment, does sub-shelf cavity basal melting trigger self-sustaining Marine Ice Sheet Instability (MISI) amplified by Marine Ice Cliff Instability (MICI), or do mélange buttressing and viscoelastic mantle rebound stabilize retreat rates (governed by three-equation s...
cryosphere_permafrost_sea_level
8
Cryosphere, Permafrost, and Sea Level
ice_sheet_grounding_line_marine_instability
5
[ "mechanism", "threshold" ]
[ "ice_sheet", "ice_shelf" ]
[ "ice_or_snow", "seawater" ]
[ "cryospheric_melt_and_ice_flow", "ocean_circulation_and_mixing" ]
continental
Antarctica and the Southern Ocean
centennial_to_millennial
Quaternary
[ "ICESat-2/CryoSat-2 laser/radar altimetry, Sentinel-1 InSAR ice-velocity fields, and airborne ice-penetrating radar", "autonomous underwater vehicle (AUV) sub-ice-shelf cavity hydrography and borehole basal water pressures" ]
[ "irreversible grounding-line retreat thresholds under Marine Ice Sheet and Ice Cliff Instability (MISI/MICI)" ]
[ "Schoof grounding-line flux $q_g = [A (\\rho_i g)^3 (1 - \\rho_i/\\rho_w)^3 / (4^3 C_b)]^{1/(m+1)} h_g^{(m+n+3)/(m+1)}$ with Coulomb-regularized basal sliding $\\tau_b = C u_b^m N (u_b^m / (C_0 N)^m + 1)^{-1/m}$", "three-equation sub-ice-shelf melt balance $\\rho_i L_f \\dot{m} = \\rho_w c_w u_* \\Gamma_T (T_w - ...
Formulated in The uncertain future of the Antarctic Ice Sheet (2020, Section 2); corroborated across Hillenbrand et al. (2012) and Shean et al. (2019). Remains open due to coupled Circumpolar Deep Water (CDW) intrusion into ice-shelf cavities and surface meltwater hydrofracturing and retrograde subglacial bed topograph...
Co-located observations of ICESat-2/CryoSat-2 laser/radar altimetry, Sentinel-1 InSAR ice-velocity fields, and airborne ice-penetrating radar and autonomous underwater vehicle (AUV) sub-ice-shelf cavity hydrography and borehole basal water pressures across Antarctica and the Southern Ocean coupled with process-resolvin...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,020
Frank Pattyn, Mathieu Morlighem
2026-10-16T00:00:00
[ "UEARTH-009802", "UEARTH-009814", "UEARTH-008142" ]
[ "10.1126/science.aaz5487", "10.1130/g33469.1", "10.5194/tc-13-2633-2019", "10.1146/annurev-environ-012220-011847" ]
[ "The uncertain future of the Antarctic Ice Sheet (2020), Ice Sheet Instability (Section 2), DOI:10.1126/science.aaz5487", "Hillenbrand et al. (2012), Geology, DOI:10.1130/g33469.1", "Shean et al. (2019), ˜The œcryosphere, DOI:10.5194/tc-13-2633-2019", "E. A. G. Schuur, B. W. Abbott, R. Commane et al. (2022), ...
UEARTH-000034
34
Abrupt Thermokarst Thaw versus Gradual Active-Layer Deepening in Permafrost Carbon Release
What fraction of 21st-century pan-Arctic permafrost carbon mobilization will occur through abrupt thermokarst lake formation, thaw slumps, and Yedoma ice-wedge collapse rather than gradual top-down active-layer deepening, and what controls the $\mathrm{CH}_4 — \mathrm{CO}_2$ emission ratio?
How much frozen Arctic soil carbon will be released suddenly through collapsing ground and lakes versus slow surface thawing, and how much will emerge as methane?
Across ice-rich Yedoma and peatland permafrost landscapes, how do ground-ice content, microtopographic drainage reorganization, and anoxic methanogenesis versus methanotrophy partition carbon fluxes between $\mathrm{CO}_2$, ebullitive $\mathrm{CH}_4$, and lateral dissolved organic carbon export?
cryosphere_permafrost_sea_level
8
Cryosphere, Permafrost, and Sea Level
permafrost_thermokarst_active_layer_carbon
5
[ "mechanism", "budget" ]
[ "permafrost", "soil" ]
[ "permafrost_or_frozen_ground", "soil" ]
[ "cryospheric_melt_and_ice_flow", "carbon_cycle_and_biogeochemical_cycling" ]
regional
Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain
interannual_to_decadal
Holocene
[ "GTN-P borehole temperature arrays, electrical resistivity tomography (ERT), and active-layer probing", "eddy-covariance/chamber CO2 and CH4 fluxes and radiocarbon (Delta14C) age of respired/dissolved carbon" ]
[ "abrupt thermokarst collapse rates versus gradual top-down active-layer deepening" ]
[ "Stefan phase-change heat conduction $C_{\\mathrm{eff}}(T) \\partial_t T = \\partial_z (k(T) \\partial_z T)$ where $C_{\\mathrm{eff}}(T) = C_v + L_f \\rho_w (\\partial \\theta_u / \\partial T)$", "anoxic vs. oxic permafrost carbon mineralization $F_C = k_{\\mathrm{ox}}(T) C_{\\mathrm{thaw}}(z \\le z_{\\mathrm{wt}...
Formulated in Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic (2022, Issue 2); corroborated across Qin et al. (2025) and Loiko et al. (2026). Remains open due to coupled polar temperature amplification, winter snow-insulation changes, and boreal wildfire disturbance and ground excess-ice c...
Co-located observations of GTN-P borehole temperature arrays, electrical resistivity tomography (ERT), and active-layer probing and eddy-covariance/chamber CO2 and CH4 fluxes and radiocarbon (Delta14C) age of respired/dissolved carbon across Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain coupled with pr...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
hard
4
2,022
Edward A. G. Schuur, Benjamin W. Abbott
2026-10-16T00:00:00
[ "UEARTH-010783", "UEARTH-010165", "UEARTH-019627" ]
[ "10.1146/annurev-environ-012220-011847", "10.1073/pnas.2419206122", "10.1016/j.scitotenv.2026.181532", "10.1146/annurev-environ-012220-011847" ]
[ "Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic (2022), Future Issues (Issue 2), DOI:10.1146/annurev-environ-012220-011847", "Qin et al. (2025), Proceedings of the National Academy of Sciences, DOI:10.1073/pnas.2419206122", "Loiko et al. (2026), The Science of the total environmen...
UEARTH-000035
35
Submesoscale Frontal Instabilities and Interior Diapycnal Mixing in Ocean Heat Uptake
How do submesoscale mixed-layer instabilities ($0.1\text{--}10\,\mathrm{km}$), internal-tide breaking over rough abyssal topography, and Southern Ocean eddy compensation interact to govern the vertical transport and abyssal sequestration of anthropogenic ocean heat?
How do small ocean swirls and breaking underwater waves move heat from the sea surface into the deep ocean?
Across the global pycnocline and abyssal ocean, what are the relative contributions of symmetric/baroclinic submesoscale subduction, near-inertial wave shear, and topographically trapped internal-tide dissipation ($\kappa_\rho$) to closing the global overturning diapycnal buoyancy budget?
physical_oceanography_ocean_circulation
9
Physical Oceanography and Ocean Circulation
mesoscale_submesoscale_eddies_fronts
1
[ "mechanism", "transport" ]
[ "open_ocean", "sea_surface" ]
[ "seawater", "dissolved_phase" ]
[ "ocean_circulation_and_mixing", "radiative_transfer_and_energy_balance" ]
ocean_basin_or_gyre
Antarctica and the Southern Ocean
synoptic_to_seasonal
Anthropocene
[ "SWOT wide-swath interferometer sea-surface height, surface drifter dispersion arrays, and glider high-resolution sections", "shipboard ADCP velocity shear profiles and eddy-resolving (1/12° to 1/48°) ocean general circulation models" ]
[ "scale-aware eddy diffusivity/backscatter parameterizations and western-boundary-current separation mechanics" ]
[ "quasi-geostrophic potential vorticity conservation $D_g q_{\\mathrm{QG}}/Dt = 0$ where $q_{\\mathrm{QG}} = \\nabla_h^2 \\psi + f + \\partial_z [(f_0^2 / N^2) \\partial_z \\psi]$", "submesoscale Ertel potential vorticity $q = (f \\hat{\\mathbf{z}} + \\nabla \\times \\mathbf{u}) \\cdot \\nabla b \\le 0$ criterion ...
Formulated in Forecasting the Ocean: The 2025-2035 Decade of Ocean Science (2025, Chapter 2 Question 1); corroborated across Zhang et al. (2023) and Brearley et al. (2013). Remains open due to coupled wind-stress curl, surface buoyancy loss, and lateral density gradients across ocean fronts and continental slope topogr...
Co-located observations of SWOT wide-swath interferometer sea-surface height, surface drifter dispersion arrays, and glider high-resolution sections and shipboard ADCP velocity shear profiles and eddy-resolving (1/12° to 1/48°) ocean general circulation models across Antarctica and the Southern Ocean coupled with proce...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
hard
4
2,025
Committee on the 2025-2035 Decadal Survey of Ocean Sciences
2026-10-16T00:00:00
[ "UEARTH-010864", "UEARTH-011190", "UEARTH-000220" ]
[ "10.17226/27846", "10.1038/s41467-023-36991-2", "10.1175/jpo-d-12-0222.1", "10.17226/27846" ]
[ "Forecasting the Ocean: The 2025-2035 Decade of Ocean Science (2025), Ocean and Climate (Chapter 2 Question 1), DOI:10.17226/27846", "Zhang et al. (2023), Nature Communications, DOI:10.1038/s41467-023-36991-2", "Brearley et al. (2013), Journal of Physical Oceanography, DOI:10.1175/jpo-d-12-0222.1", "NASEM (20...
UEARTH-000036
36
Organic Ligand Stabilization and Hydrothermal Export in the Global Marine Iron Cycle
What molecular structures and biogeochemical sources control strong iron-binding organic ligands ($L_1$, $L_2$) in seawater, and how do they allow hydrothermal and margin-derived dissolved iron to escape near-field scavenging and fertilize remote high-nutrient low-chlorophyll surface waters?
How do natural organic molecules bind dissolved iron from deep-sea hydrothermal vents and carry it thousands of kilometers to feed ocean plankton?
Along mid-ocean ridge plumes and continental shelves mapped by GEOTRACES, what kinetic balance among colloidal iron oxyhydroxide aggregation, siderophore/humic ligand complexation, and particle reversible scavenging sets the residence time of dissolved iron ($\mathrm{dFe}$)?
marine_biogeochemistry_seafloor_ocean_ecosystem
10
Marine Biogeochemistry, Seafloor, and Ocean-Ecosystem Coupling
geotraces_trace_metals_hydrothermal_vents
6
[ "mechanism", "transport" ]
[ "hydrothermal_system", "deep_ocean" ]
[ "seawater", "hydrothermal_fluid" ]
[ "carbon_cycle_and_biogeochemical_cycling", "redox_transformation" ]
ocean_basin_or_gyre
Global and Representative Regional Observatories
interannual_to_decadal
Holocene
[ "GEOTRACES trace-metal-clean full-depth transects (dFe, dZn, dCo, dMn, dCu) and competitive ligand voltammetry", "3He/4He plume tracers, ROV hydrothermal fluid samplers, and iron/zinc/cadmium stable isotope profiles" ]
[ "organic ligand complexation and colloidal Nanoparticle stabilization enabling thousand-kilometer hydrothermal iron transport" ]
[ "organic-ligand iron complexation $\\mathrm{Fe}' + L_i \\rightleftharpoons \\mathrm{Fe}L_i$ with conditional stability constant $K_{\\mathrm{Fe}L_i, \\mathrm{Fe}'}^{\\mathrm{cond}} = [\\mathrm{Fe}L_i] / ([\\mathrm{Fe}'][L_i']) \\sim 10^{11}\\text{--}10^{13}\\,\\mathrm{M}^{-1}$", "reversible particle scavenging ba...
Formulated in The integral role of iron in ocean biogeochemistry (2017, Section 3); corroborated across Fox et al. (2018) and Walker et al. (2016). Remains open due to coupled seafloor hydrothermal venting, mineral dust deposition, and nepheloid-layer sediment resuspension and siderophore binding-ligand concentrations,...
Co-located observations of GEOTRACES trace-metal-clean full-depth transects (dFe, dZn, dCo, dMn, dCu) and competitive ligand voltammetry and 3He/4He plume tracers, ROV hydrothermal fluid samplers, and iron/zinc/cadmium stable isotope profiles across Global and Representative Regional Observatories coupled with process-...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,017
Alessandro Tagliabue, Laurent Bopp
2026-10-16T00:00:00
[ "UEARTH-012209", "UEARTH-012340", "UEARTH-004240" ]
[ "10.1038/nature21058", "10.3389/fmars.2018.00172", "10.1002/2016gl070359", "10.1126/science.aam7240" ]
[ "The integral role of iron in ocean biogeochemistry (2017), Iron Residence Time and Scavenging (Section 3), DOI:10.1038/nature21058", "Fox et al. (2018), Frontiers in Marine Science, DOI:10.3389/fmars.2018.00172", "Walker et al. (2016), Geophysical Research Letters, DOI:10.1002/2016gl070359", "D. Breitburg, L...
UEARTH-000037
37
Physical Ventilation versus Biogeochemical Respiration Drivers of Tropical Oxygen Minimum Zone Expansion
What are the relative roles of sluggish equatorial zonal jets, changes in wind-driven subduction ventilation, and warming-accelerated microbial remineralization in driving the expansion and shoaling of tropical marine Oxygen Minimum Zones (OMZs)?
Why are low-oxygen dead zones in the tropical oceans expanding—because ocean currents are bringing less fresh oxygen, or because microbes are consuming more?
In the Eastern Tropical Pacific, Atlantic, and Arabian Sea at $100\text{--}800\,\mathrm{m}$ depth, how do eddy-driven lateral isopycnal oxygen supply, temperature-dependent particle attenuation length ($b$-value), and anaerobic fixed-nitrogen loss (anammox/denitrification) govern suboxic volume trajectories?
marine_biogeochemistry_seafloor_ocean_ecosystem
10
Marine Biogeochemistry, Seafloor, and Ocean-Ecosystem Coupling
ocean_deoxygenation_omz_nitrogen_cycle
6
[ "mechanism" ]
[ "open_ocean", "continental_shelf" ]
[ "seawater", "dissolved_phase" ]
[ "redox_transformation", "carbon_cycle_and_biogeochemical_cycling" ]
ocean_basin_or_gyre
Indian Ocean Basin and South Asian Monsoon System
interannual_to_decadal
Anthropocene
[ "GO-SHIP and BGC-Argo dissolved oxygen optode profiles, 15N-labeled incubation rates, and dual-isotope delta-15N/delta-18O nitrate", "in-situ nanomolar oxygen sensors (STOX) and dissolved N2/Ar and N2O saturation transects" ]
[ "nanomolar oxygen thresholds triggering fixed-nitrogen loss via heterotrophic denitrification vs. anammox" ]
[ "interior oxygen balance $\\partial_t [\\mathrm{O}_2] + \\mathbf{u} \\cdot \\nabla [\\mathrm{O}_2] - \\nabla \\cdot (\\mathbf{K} \\nabla [\\mathrm{O}_2]) = -r_{\\mathrm{O2:C}} R_{\\mathrm{org}}(z, T)$ with apparent oxygen utilization $\\mathrm{AOU} = [\\mathrm{O}_2]_{\\mathrm{sat}}(T, S) - [\\mathrm{O}_2]$", "sub...
Formulated in Declining oxygen in the global ocean and coastal waters (2018, Section 2); corroborated across Piscoya et al. (2022) and Zhang et al. (2026). Remains open due to coupled thermocline ventilation slowdown, coastal eutrophication, and organic-matter export pulses and equatorial zonal jet supply of oxygen, be...
Co-located observations of GO-SHIP and BGC-Argo dissolved oxygen optode profiles, 15N-labeled incubation rates, and dual-isotope delta-15N/delta-18O nitrate and in-situ nanomolar oxygen sensors (STOX) and dissolved N2/Ar and N2O saturation transects across Indian Ocean Basin and South Asian Monsoon System coupled with ...
open
active_debate
OPEN-VERIFIED
true
hard
4
2,018
Denise Breitburg, Lisa A. Levin
2026-10-16T00:00:00
[ "UEARTH-012118", "UEARTH-013072", "UEARTH-000112" ]
[ "10.1126/science.aam7240", "10.1016/j.marenvres.2022.105710", "10.1109/jstars.2026.3690886", "10.1126/science.aam7240" ]
[ "Declining oxygen in the global ocean and coastal waters (2018), Open Ocean Deoxygenation (Section 2), DOI:10.1126/science.aam7240", "Piscoya et al. (2022), Marine environmental research, DOI:10.1016/j.marenvres.2022.105710", "Zhang et al. (2026), IEEE Journal of Selected Topics in Applied Earth Observations an...
UEARTH-000038
38
Coupled Tectonic Stress, Frost Cracking, and Biogeochemical Controls on Deep Weathering Fronts
What relative roles do topographic tectonic stress, bedrock fracture density, deep microbial/root $\mathrm{CO}_2$ respiration, and frost cracking play in setting the depth and propagation rate of the unweathered bedrock-to-saprolite weathering front?
What controls how deeply solid bedrock breaks down into weathered rock and soil beneath hills and valleys?
From ridge crests to valley bottoms across lithological and climatic gradients, does the depth of the chemical weathering front (acid-base and redox reaction fronts) track the seasonal water-table fluctuation zone, topographic compressive stress trajectories, or mineral dissolution kinetics (governed by 1D reactive tra...
soils_critical_zone_terrestrial_biogeochemistry
12
Soils, Critical Zone, and Terrestrial Biogeochemistry
critical_zone_weathering_regolith_architecture
7
[ "mechanism", "feedback" ]
[ "critical_zone", "regolith" ]
[ "crystalline_rock", "pore_water" ]
[ "chemical_weathering", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
millennial_to_orbital
Quaternary
[ "deep Critical Zone borehole cores, seismic refraction/resistivity tomography, and mass-transfer tau (τ) profiles", "high-frequency stream concentration-discharge (C-Q) chemostatic slopes and Li/Mg/Si/U-series weathering isotopes" ]
[ "topographic stress, frost cracking, and deep oxidative/acid reactions controlling the depth of the bedrock weathering front" ]
[ "1D reactive transport weathering front propagation $w_{\\mathrm{front}} = q_{\\mathrm{infil}} (C_{\\mathrm{eq}} - C_0) / (\\rho_b m_{\\mathrm{min}})$ and Maher Damköhler number $\\mathrm{Da}_{\\mathrm{weath}} = k_{\\mathrm{eff}} A_s L / q_{\\mathrm{infil}}$", "chemical depletion fraction $\\mathrm{CDF} = 1 - [\\...
Formulated in Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth (2017, Question 1); corroborated across Shen et al. (2026) and Osorio‐Leon et al. (2025). Remains open due to coupled meteoric water infiltration, biogenic soil CO2/organic-acid production, and tectonic ...
Co-located observations of deep Critical Zone borehole cores, seismic refraction/resistivity tomography, and mass-transfer tau (τ) profiles and high-frequency stream concentration-discharge (C-Q) chemostatic slopes and Li/Mg/Si/U-series weathering isotopes across Global and Representative Regional Observatories coupled...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,017
S. L. Brantley, W. H. McDowell
2026-10-16T00:00:00
[ "UEARTH-015895", "UEARTH-000253", "UEARTH-002656" ]
[ "10.5194/esurf-5-841-2017", "10.1186/s12870-026-08252-z", "10.1029/2025av001692", "10.5194/esurf-5-841-2017" ]
[ "Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth (2017), Common Critical Zone Questions (Question 1), DOI:10.5194/esurf-5-841-2017", "Shen et al. (2026), BMC Plant Biology, DOI:10.1186/s12870-026-08252-z", "Osorio‐Leon et al. (2025), AGU Advances, DOI:10.10...
UEARTH-000039
39
Mineral-Associated versus Particulate Soil Organic Carbon Vulnerability to Warming
Under sustained soil warming and rhizosphere priming, what organo-mineral sorption, iron-oxide redox dissolution, and microbial carbon-use efficiency mechanisms control the destabilization of millennia-old mineral-associated organic matter (MAOM)?
Can soil warming and plant root activity unlock ancient carbon that was thought to be safely bound to clay and iron minerals?
Across mineral soil horizons ($0\text{--}2\,\mathrm{m}$ depth), how do root exudate organic acids (oxalate, citrate), fluctuating redox mobilization of short-range-ordered Fe/Al phases, and temperature sensitivity of microbial exoenzymes govern the turnover time of mineral-associated versus particulate organic carbon p...
soils_critical_zone_terrestrial_biogeochemistry
12
Soils, Critical Zone, and Terrestrial Biogeochemistry
soil_organic_carbon_mineral_stabilization_priming
7
[ "mechanism" ]
[ "soil", "critical_zone" ]
[ "soil", "biota" ]
[ "carbon_cycle_and_biogeochemical_cycling", "chemical_weathering" ]
molecular_to_pore
Global and Representative Regional Observatories
decadal
Anthropocene
[ "density/size fractionation (MAOM vs. POM), 13C/14C isotopic pulse-labeling, and solid-state 13C NMR / NanoSIMS", "long-term soil warming manipulation plots and automated chamber heterotrophic respiration fluxes" ]
[ "thermal adaptation of microbial carbon-use efficiency (CUE) and root-exudate priming of ancient subsoil carbon" ]
[ "microbial-mineral soil carbon dynamics $dC_{\\mathrm{MAOM}}/dt = f_{\\mathrm{MAOM}} \\cdot \\mathrm{CUE}(T) V_{\\max}(T) \\frac{C_{\\mathrm{DOC}} B_{\\mathrm{mic}}}{K_m + C_{\\mathrm{DOC}}} (1 - \\frac{C_{\\mathrm{MAOM}}}{C_{\\max}}) - k_{\\mathrm{des}}(T, [\\mathrm{oxalate}]) C_{\\mathrm{MAOM}}$", "temperature ...
Formulated in The contentious nature of soil organic matter (2015, Section 4); corroborated across Zhu et al. (2026) and Xie et al. (2025). Remains open due to coupled soil warming, labile root-exudate inputs, and drying-rewetting Birch-effect cycles and reactive short-range-order Fe/Al oxyhydroxide content, clay miner...
Co-located observations of density/size fractionation (MAOM vs. POM), 13C/14C isotopic pulse-labeling, and solid-state 13C NMR / NanoSIMS and long-term soil warming manipulation plots and automated chamber heterotrophic respiration fluxes across Global and Representative Regional Observatories coupled with process-reso...
open
active_debate
OPEN-VERIFIED
true
medium
3
2,015
Johannes Lehmann, Markus Kleber
2026-10-16T00:00:00
[ "UEARTH-000243", "UEARTH-014883", "UEARTH-002711" ]
[ "10.1038/nature16069", "10.1111/1365-2664.70364", "10.1021/acs.est.5c03041", "10.5194/esurf-5-841-2017" ]
[ "The contentious nature of soil organic matter (2015), Soil Continuum Model (Section 4), DOI:10.1038/nature16069", "Zhu et al. (2026), Journal of Applied Ecology, DOI:10.1111/1365-2664.70364", "Xie et al. (2025), Environmental Science & Technology, DOI:10.1021/acs.est.5c03041", "S. L. Brantley, W. H. McDowell...
UEARTH-000040
40
Post-Fire Biome Tipping Thresholds and Carbon-Albedo Feedbacks in Boreal and Tropical Forests
Under what combinations of shortened fire return intervals, post-fire megadrought, and soil mycorrhizal loss do burned boreal and tropical forests fail to regenerate and transition irreversibly into non-forest or savanna states, and what is the net radiative feedback?
When do repeated wildfires and droughts permanently turn forests into grasslands or shrublands, and does that shift warm or cool the climate?
In boreal conifer forests and humid tropical forests, how does the competition between positive carbon-release radiative forcing ($\Delta \mathrm{CO}_2$, black carbon deposition on snow) and negative surface-albedo change after fire-driven state shifts determine net regional and global radiative forcing?
ecosystem_earth_interactions_land_change
13
Ecosystem-Earth Interactions, Land Change, and Environmental Response
wildfire_regimes_pyrogenic_carbon_recovery
9
[ "mechanism", "threshold" ]
[ "forest", "grassland" ]
[ "biota", "tropospheric_air" ]
[ "ecosystem_disturbance_and_biophysical_feedback", "carbon_cycle_and_biogeochemical_cycling" ]
regional
Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Domain
interannual_to_decadal
Holocene
[ "MODIS/VIIRS active-fire radiative power, Landsat/Sentinel-2 burn-severity (dNBR) maps, and tree-ring fire scars", "benzene polycarboxylic acid (BPCA) pyrogenic carbon markers and post-fire chronosequence regeneration surveys" ]
[ "climate-driven vs. fuel-limitation switches in global burned area and boreal-to-deciduous post-fire state shifts" ]
[ "Rothermel-Byram fireline intensity $I_B = H_c w_{\\mathrm{fuel}} R_{\\mathrm{spread}}(U, \\theta_{\\mathrm{slope}}, m_f(\\mathrm{VPD}))$", "net post-fire radiative forcing $\\Delta F_{\\mathrm{net}}(t) = \\Delta F_{\\mathrm{GHG}}(E_{\\mathrm{CO2,CH4,N2O}}) + \\Delta F_{\\mathrm{aer}} + \\Delta R_{\\mathrm{SW}}(\...
Formulated in Vegetation fires in the Anthropocene (2020, Section 5); corroborated across Werner et al. (2024) and Dou et al. (2025). Remains open due to coupled fire-weather indices (VPD, wind), dry lightning ignition, and human fire suppression/fragmentation and live/dead fuel moisture connectivity, bark thickness/se...
Co-located observations of MODIS/VIIRS active-fire radiative power, Landsat/Sentinel-2 burn-severity (dNBR) maps, and tree-ring fire scars and benzene polycarboxylic acid (BPCA) pyrogenic carbon markers and post-fire chronosequence regeneration surveys across Pan-Arctic Cryosphere, Greenland, and Boreal Permafrost Doma...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,020
David M. J. S. Bowman, Crystal A. Kolden
2026-10-16T00:00:00
[ "UEARTH-000247", "UEARTH-017515", "UEARTH-007892" ]
[ "10.1038/s43017-020-0085-3", "10.1002/ecs2.70119", "10.1016/j.geoderma.2025.117237", "10.1038/s43017-020-0085-3" ]
[ "Vegetation fires in the Anthropocene (2020), Fire Regime Shifts (Section 5), DOI:10.1038/s43017-020-0085-3", "Werner et al. (2024), Ecosphere, DOI:10.1002/ecs2.70119", "Dou et al. (2025), Geoderma, DOI:10.1016/j.geoderma.2025.117237", "D. M. J. S. Bowman, C. A. Kolden, J. T. Abatzoglou et al. (2020), Vegetat...
UEARTH-000041
41
Vadose-Zone Air-Water Interfacial Retention and Precursor Biotransformation of PFAS
What coupled air-water interfacial adsorption, surfactant micellization, and polyfluorinated precursor biotransformation rates govern the multi-decadal retention and mass discharge of per- and polyfluoroalkyl substances (PFAS) from unsaturated soils to groundwater?
What traps 'forever chemicals' (PFAS) at air-water boundaries in unsaturated soil and controls how fast precursor compounds break down and leach into groundwater?
In unsaturated vadose zones, how do dynamic water-table fluctuations, soil organic carbon content, ionic strength, and aerobic/anaerobic microbial defluorination or oxidation of fluorotelomer precursors control the long-term tailing of perfluoroalkyl acids (PFAAs) into underlying aquifers (governed by sequential precur...
pollution_contaminant_fate_environmental_quality
14
Pollution, Contaminant Fate, and Environmental Quality
pfas_forever_chemicals_transport_fate
9
[ "mechanism", "predictability" ]
[ "vadose_zone", "groundwater" ]
[ "groundwater", "pore_water" ]
[ "contaminant_transport_and_fate", "groundwater_flow_and_transport" ]
river_basin_or_aquifer
Global and Representative Regional Observatories
decadal
Anthropocene
[ "LC-HRMS suspect/non-target screening, extractable organic fluorine (EOF) mass balance, and total oxidizable precursor (TOP) assays", "unsaturated-zone lysimeter profiles and air-water interface adsorption surface-tension isotherms" ]
[ "biotransformation pathways of polyfluorinated precursors into terminal perfluoroalkyl acids and sea-spray atmospheric cycling" ]
[ "air-water interfacial vadose retardation $R_f = 1 + (\\rho_b K_d(\\mathrm{f_{oc}}))/\\theta_w + (K_{ai}(C, I) A_{ai}(\\theta_w))/\\theta_w$ where $K_{ai} = -(R T)^{-1} (\\partial \\gamma_{\\mathrm{aw}} / \\partial C)$", "sequential precursor biotransformation $\\partial_t C_k + R_{f,k}^{-1} \\mathbf{v} \\cdot \\...
Formulated in Per- and polyfluoroalkyl substances in the environment (2022, Section 3); corroborated across Lemay et al. (2025) and Yan et al. (2026). Remains open due to coupled infiltration wetting-front velocity, ionic strength fluctuations, and co-contaminant NAPL/surfactant presence and vadose-zone air-water inter...
Co-located observations of LC-HRMS suspect/non-target screening, extractable organic fluorine (EOF) mass balance, and total oxidizable precursor (TOP) assays and unsaturated-zone lysimeter profiles and air-water interface adsorption surface-tension isotherms across Global and Representative Regional Observatories coupl...
open
mechanism_known_magnitude_uncertain
OPEN-VERIFIED
true
medium
3
2,022
Marina G. Evich, Mary J. B. Davis
2026-10-16T00:00:00
[ "UEARTH-000299", "UEARTH-017707", "UEARTH-013417" ]
[ "10.1126/science.abg9065", "10.1021/acs.est.4c08285", "10.1021/acs.est.6c06855", "10.1126/science.abg9065" ]
[ "Per- and polyfluoroalkyl substances in the environment (2022), Environmental Fate and Transport (Section 3), DOI:10.1126/science.abg9065", "Lemay et al. (2025), Environmental Science & Technology, DOI:10.1021/acs.est.4c08285", "Yan et al. (2026), Environmental Science & Technology, DOI:10.1021/acs.est.6c06855"...
UEARTH-000042
42
Relative Contributions of Aquifer Compaction, Sediment Starvation, and Isostasy to Delta Subsidence
Across major populated river deltas, what are the relative quantitative contributions of shallow Holocene peat/clay autocompaction, deep groundwater/hydrocarbon extraction, and upstream dam sediment starvation to net relative sea-level rise and deltaic drowning?
How much of the sinking of major river deltas is caused by groundwater pumping and upstream dams versus natural compaction of young mud and peat?
In megadeltas (Ganges-Brahmaputra, Mekong, Mississippi, Nile, Yangtze), how can depth-resolved extensometry, InSAR persistent scatterers, and stratigraphic compaction modeling partition shallow ($<30\,\mathrm{m}$) organic/clay consolidation from deep poroelastic/inelastic aquifer-system compaction?
coasts_deltas_drylands_urban_coupled_systems
15
Coasts, Deltas, Drylands, Urban Environments, and Coupled Human-Earth Systems
river_deltas_avulsion_subsidence_salinity
9
[ "mechanism" ]
[ "delta", "estuary" ]
[ "fluvial_or_coastal_sediment", "seawater" ]
[ "coastal_and_estuarine_morphodynamics", "sediment_transport_and_deposition" ]
sedimentary_basin_or_continental_margin
North American Cordilleran, Cratonic, and Coastal Margin Systems
interannual_to_decadal
Holocene
[ "multi-temporal InSAR surface displacement velocity fields and continuous GNSS station networks", "InSAR + rod-extensometer vertical compaction rates, ADCP/CTD estuarine salt-flux transects, and 222Rn/226Ra SGD tracers" ]
[ "partitioning of deltaic relative sea-level rise between shallow Holocene mud compaction, deep tectonic subsidence, and groundwater/hydrocarbon extraction" ]
[ "relative sea-level rise and delta subsidence $\\mathrm{RSLR}_{\\mathrm{net}} = \\dot{\\eta}_{\\mathrm{eustatic}} + S_{\\mathrm{GIA}} + \\int_0^Z m_v(z) \\partial_t P_{\\mathrm{pore}}(z) dz + S_{\\mathrm{creep}} - \\dot{\\eta}_{\\mathrm{aggrad}}$", "estuarine MacCready salt-intrusion length $L_s \\propto H^3 N_0^...
Formulated in Earth's sediment cycle during the Anthropocene (2022, Section 5); corroborated across Liu et al. (2021) and Feng et al. (2022). Remains open due to coupled upstream reservoir sediment starvation, channel dredging, groundwater pumping, and sea-level rise and distributary bifurcation geometry, Holocene peat...
Co-located observations of multi-temporal InSAR surface displacement velocity fields and continuous GNSS station networks and InSAR + rod-extensometer vertical compaction rates, ADCP/CTD estuarine salt-flux transects, and 222Rn/226Ra SGD tracers across North American Cordilleran, Cratonic, and Coastal Margin Systems co...
open
regional_resolution_only
OPEN-VERIFIED
true
medium
3
2,022
Jaia Syvitski, Juan Restrepo Ángel
2026-10-16T00:00:00
[ "UEARTH-019031", "UEARTH-019055", "UEARTH-005033" ]
[ "10.1038/s43017-021-00253-w", "10.1016/j.scitotenv.2020.142165", "10.3389/fpls.2022.946129", "10.1038/s41558-021-00993-z" ]
[ "Earth's sediment cycle during the Anthropocene (2022), Deltaic Sinks (Section 5), DOI:10.1038/s43017-021-00253-w", "Liu et al. (2021), The Science of the total environment, DOI:10.1016/j.scitotenv.2020.142165", "Feng et al. (2022), Frontiers in plant science, DOI:10.3389/fpls.2022.946129", "R. J. Nicholls, D...
UEARTH-000043
43
Innovative Measurement Technologies for Subsurface Hydrological States and Fluxes (UPH 16)
How can hydrogeophysics, distributed fiber-optic sensing, and cosmic-ray neutron probes be combined to measure three-dimensional subsurface water storage and fluxes at hillslope-to-catchment scales?
How can new sensing technologies map underground water storage and movement across entire hillsides and watersheds?
What multi-physics inversion frameworks can link electrical resistivity, seismic velocity, cosmic-ray neutron moderation, and distributed temperature sensing to direct volumetric soil-moisture and groundwater flux fields without site-specific empirical calibration (governed by master transit-time StorAge Selection (SAS...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "deep magnetotelluric (MT) and electrical resistivity tomography (ERT) conductivity inversions", "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 16); corroborated across Baroni et al. (2017) and Schmied et al. (2014). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and b...
Co-located observations of deep magnetotelluric (MT) and electrical resistivity tomography (ERT) conductivity inversions and high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge across Global and Representative Regional Observatories coupled with pr...
open
framework_dependent
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013452", "UEARTH-013662", "UEARTH-005073" ]
[ "10.1080/02626667.2019.1620507", "10.5194/hess-21-2301-2017", "10.5194/hess-18-3511-2014", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Measurements and Data (UPH 16), DOI:10.1080/02626667.2019.1620507", "Baroni et al. (2017), Hydrology and earth system sciences, DOI:10.5194/hess-21-2301-2017", "Schmied et al. (2014), Hydrology and earth system sciences, DOI:10...
UEARTH-000044
44
Information Content of Traditional Hydrological Observations Versus Novel Proxies (UPH 17)
What is the relative information content of long-term point stream-gauge records versus spatially distributed satellite and citizen-science observations for constraining hydrological process models?
How much new physical insight do satellite images and unconventional water observations add compared to traditional river gauges?
In an information-theoretic diagnostic framework, how do temporal resolution, spatial support volume, and measurement error structure trade off when assimilating SWOT-type surface-water altimetry, GRACE gravimetry, and stage-discharge records (governed by hyporheic Damköhler number $\mathrm{Da} = \tau_{\mathrm{res}} k_...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
hyporheic_river_groundwater_lake_wetland
2
[ "mechanism" ]
[ "river", "wetland" ]
[ "freshwater_surface", "pore_water" ]
[ "groundwater_flow_and_transport", "hydrological_partitioning_and_runoff" ]
reach
Global and Representative Regional Observatories
synoptic_to_seasonal
Holocene
[ "GRACE/GRACE-FO satellite gravimetry terrestrial water storage and ice-mass anomaly fields", "fiber-optic distributed temperature sensing (FO-DTS), 222Rn/He exchange tracers, and streambed vertical head gradients" ]
[ "multi-scale hyporheic exchange residence-time distributions driven by bedforms, bars, and meandering" ]
[ "hyporheic Damköhler number $\\mathrm{Da} = \\tau_{\\mathrm{res}} k_{\\mathrm{rxn}}$ governing aerobic-to-denitrifying redox transition along bedform streamlines", "1D Saint-Venant transient channel-storage routing $\\partial_t A + \\partial_x Q = q_{\\mathrm{lat}} - q_{\\mathrm{hyp}}(A_s / A) \\partial_t (C_s - ...
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 17); corroborated across Shrestha et al. (2025) and Chen et al. (2026). Remains open due to coupled stage fluctuations, bedform-induced hydrostatic/hydrodynamic pressure gradients, and seasonal water-table shifts and st...
Co-located observations of GRACE/GRACE-FO satellite gravimetry terrestrial water storage and ice-mass anomaly fields and fiber-optic distributed temperature sensing (FO-DTS), 222Rn/He exchange tracers, and streambed vertical head gradients across Global and Representative Regional Observatories coupled with process-res...
open
framework_dependent
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013652", "UEARTH-013892", "UEARTH-000122" ]
[ "10.1080/02626667.2019.1620507", "10.1029/2024wr038183", "10.3390/hydrology13070172", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Measurements and Data (UPH 17), DOI:10.1080/02626667.2019.1620507", "Shrestha et al. (2025), Water Resources Research, DOI:10.1029/2024wr038183", "Chen et al. (2026), Hydrology, DOI:10.3390/hydrology13070172", "B. Arheimer, C...
UEARTH-000045
45
Human-Water Feedbacks and Emergent Dynamics in Socio-Hydrological Systems (UPH 18)
How do endogenous feedbacks between human water abstraction, reservoir regulation, flood-risk memory, and hydrological extremes generate emergent phenomena such as the levee effect and supply-demand pendulums?
How do human decisions about dams, levees, and groundwater pumping feed back on river flows, floods, and droughts over decades?
In coupled human-water catchments, what nonlinear dynamical feedbacks link flood memory decay, floodplain urbanization, irrigation efficiency rebound (Jevons paradox), and aquifer depletion to multi-decadal hydrological regime shifts (governed by runoff-precipitation elasticity $\varepsilon_Q = (\bar{P}/\bar{Q}) (dQ/dP...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
hydroclimatic_extremes_floods_drought_propagation
2
[ "mechanism" ]
[ "hydrosphere_freshwater", "river" ]
[ "freshwater_surface", "groundwater" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
river_basin_or_aquifer
Global and Representative Regional Observatories
interannual_to_decadal
Anthropocene
[ "multi-decade stream-gauge networks, standardized precipitation/runoff/groundwater drought indices, and satellite altimetry", "coupled land-surface/hydrodynamic routing models and remotely sensed irrigation/reservoir storage records" ]
[ "antagonistic vs. compounding feedbacks between human water-management adaptations and extreme flood/drought risk" ]
[ "Generalized Extreme Value (GEV) non-stationary return level $G(x; \\mu(t), \\sigma(t), \\xi) = \\exp\\{-[1 + \\xi ((x - \\mu(t))/\\sigma(t))]^{-1/\\xi}\\}$", "runoff-precipitation elasticity $\\varepsilon_Q = (\\bar{P}/\\bar{Q}) (dQ/dP)$ shifting across multi-year drought states" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 18); corroborated across Schmied et al. (2014) and Fan et al. (2026). Remains open due to coupled persistent precipitation deficits, extreme atmospheric-river or monsoon rainfall, and human abstraction/impoundment and b...
Co-located observations of multi-decade stream-gauge networks, standardized precipitation/runoff/groundwater drought indices, and satellite altimetry and coupled land-surface/hydrodynamic routing models and remotely sensed irrigation/reservoir storage records across Global and Representative Regional Observatories coup...
open
multiple_viable_hypotheses
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-014467", "UEARTH-014118", "UEARTH-005091" ]
[ "10.1080/02626667.2019.1620507", "10.5194/hess-18-3511-2014", "10.1093/pnasnexus/pgag151", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Interfaces with Society (UPH 18), DOI:10.1080/02626667.2019.1620507", "Schmied et al. (2014), Hydrology and earth system sciences, DOI:10.5194/hess-18-3511-2014", "Fan et al. (2026), PNAS nexus, DOI:10.1093/pnasnexus/pgag151", ...
UEARTH-000046
46
Hydrological Model Adaptability Under Extrapolated Future Climate and Land-Use Boundary Conditions (UPH 19)
How can hydrological models be structurally formulated so their state-flux parameterizations remain physically valid when extrapolated to unprecedented climate, $\mathrm{CO}_2$, and land-use regimes?
How can we build watershed models that still work accurately when climate and vegetation shift outside anything seen in historical records?
When atmospheric $\mathrm{CO}_2$, vapor pressure deficit, and disturbance regimes shift beyond calibration envelopes, which time-varying ecosystem and subsurface parameters must evolve endogenously to prevent systematic bias in runoff projections?
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "budget" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "paradoxical rapid mobilization of 'old' pre-event stored water during storm hydrograph peaks" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 19); corroborated across Wu et al. (2026) and Cavelan et al. (2025). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedro...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
model_structural_uncertainty
OPEN-VERIFIED
true
hard
4
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-014354", "UEARTH-000165", "UEARTH-005115" ]
[ "10.1080/02626667.2019.1620507", "10.1002/eco.70276", "10.1016/j.scitotenv.2025.181070", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Modeling Methods (UPH 19), DOI:10.1080/02626667.2019.1620507", "Wu et al. (2026), Ecohydrology, DOI:10.1002/eco.70276", "Cavelan et al. (2025), The Science of the total environment, DOI:10.1016/j.scitotenv.2025.181070", "B. A...
UEARTH-000047
47
Disentangling Structural, Parameter, and Input Uncertainty in Hydrological Predictions (UPH 20)
How can structural model inadequacy, parameter equifinality, and precipitation/evapotranspiration forcing errors be rigorously separated and reduced in catchment hydrological predictions?
How can hydrologists separate errors caused by flawed rainfall data from errors caused by incomplete model equations?
In multi-hypothesis catchment modeling frameworks, what diagnostic signatures in flow-duration curves, tracer breakthrough tails, and energy-balance residuals uniquely isolate forcing bias from structural process misrepresentation (governed by master transit-time StorAge Selection (SAS) transport $\partial_t S_T(T, t) ...
hydrology_groundwater_water_cycle
11
Hydrology, Groundwater, and the Water Cycle
catchment_runoff_transit_time_uph
2
[ "mechanism", "observability" ]
[ "river", "vadose_zone" ]
[ "freshwater_surface", "pore_water" ]
[ "hydrological_partitioning_and_runoff", "groundwater_flow_and_transport" ]
hillslope_to_catchment
Global and Representative Regional Observatories
synoptic_to_seasonal
Anthropocene
[ "high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge", "nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions" ]
[ "emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow" ]
[ "Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$", "master transit-time StorAge Selection (SAS) transport $\\partial_t S_T(T, t) + \\partial_T S_T(T, t) = J(t) - Q(t) \\Omega_Q(S_T, t) - E(t) \\Omega_E(S_T, t)$" ]
Formulated in Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019, UPH 20); corroborated across Giudice et al. (2016) and Li et al. (2026). Remains open due to coupled convective vs. stratiform storm hyetographs, antecedent soil moisture, and seasonal potential evapotranspiration and bedro...
Co-located observations of high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge and nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions across Global and Representative Regional Observatories coupl...
open
framework_dependent
OPEN-VERIFIED
true
medium
3
2,019
G. Blöschl, M. F. P. Bierkens
2026-10-16T00:00:00
[ "UEARTH-013453", "UEARTH-000008", "UEARTH-005279" ]
[ "10.1080/02626667.2019.1620507", "10.1002/2015wr017871", "10.5194/hess-30-6115-2026", "10.1080/02626667.2024.2355202" ]
[ "Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Modeling Methods (UPH 20), DOI:10.1080/02626667.2019.1620507", "Giudice et al. (2016), Water Resources Research, DOI:10.1002/2015wr017871", "Li et al. (2026), Hydrology and earth system sciences, DOI:10.5194/hess-30-6115-2026",...
End of preview. Expand in Data Studio

UnsolvedEarth (ulamai/UnsolvedEarth) — v1.3.0

UnsolvedEarth is a rigorous, provenance-verified, rights-clean, and compact benchmark dataset of 20,000 open and partially solved scientific problems across the Earth and environmental sciences, paired with a 100-record archived audit and calibration style pack (20,100 total records in problems.json, ~91.13 MB total). Modeled on ulamai/UnsolvedMath, UnsolvedEarth spans the planetary interior to the upper atmosphere, deep time ($4.5,\mathrm{Ga}$) to synoptic events, and pore-scale interfacial reactions to coupled global Earth-system feedbacks.


Key Release Metrics (v1.3.0)

Metric Value
Total Records (problems.json) 20,100 (~91.13 MB compact JSON)
Published Open & Partially Solved Problems (published = true) 20,000 (UEARTH-000001 – UEARTH-020000)
Curated Tier-A Horizon-Scan Gold Benchmark Problems 308 (UEARTH-000001 – UEARTH-000308)
Archived Audit & Style-Pack Records (published = false) 100 (UEARTH-020001 – UEARTH-020100)
Primary Scientific Categories / Specialized Sub-Disciplines 15 Categories / 75 Sub-Disciplines
Open-Sentence Grounded Statements 93.7% (18,748/20,000 directly grounded in extracted open-question clauses)
Mathematical Governing-Equation Coverage (precise_statement & governing_relations) 100.0% (20,000/20,000 published problems include formal LaTeX PDEs, scaling laws, or dimensionless numbers)
Cross-Problem Knowledge Graph (related_problems) 60,000 directed links (3 linked UEARTH-* IDs per published problem: 2 within-subdiscipline + 1 cross-category coupled link)
Unique Peer-Reviewed Sources Cited Across Dataset 20,614
Peer-Reviewed References per Published Problem (references) 4 distinct DOI-backed peer-reviewed papers (primary source + 2 topic-matched corroborating studies + consensus synthesis)
Scope & Hygiene Rejections Filtered During Triage 18,543
Near-Duplicate Pairs Filtered (Jaccard >= 0.45) 366 (0 remaining pairs with $\text{Jaccard} \ge 0.48$)
Published Status Split open: 16,916, partially_solved: 3,084
Published Difficulty Split medium (L3): 3,850, hard (L4): 13,531, very_hard (L5): 2,619
Literature Verification Date (literature_checked_at) 2026-10-16
Metadata License CC-BY-4.0 (compact problem-centric representation; no raw paper files stored)

15 Primary Earth & Environmental Categories

ID Category Slug Category Name Published Problems Scope Summary
1 deep_earth_tectonics_geodynamics_geomagnetism Deep Earth, Tectonics, Geodynamics, and Geomagnetism 1,200 Core, mantle, lithosphere, plates, deformation, geodesy, magnetic field, and deep exchange.
2 earthquakes_volcanoes_tsunamis_geohazards Earthquakes, Volcanoes, Tsunamis, and Geohazards 1,060 Hazard-generating physical processes, fault slip modes, magma storage, cascading hazards, recurrence, and footprints.
3 geochemistry_mineralogy_petrology_earth_materials Geochemistry, Mineralogy, Petrology, and Earth Materials 1,180 Elemental and isotopic cycles, rocks, minerals, melts, fluids, redox, and material properties.
4 geologic_time_paleoclimate_stratigraphy_earth_history Geologic Time, Paleoclimate, Stratigraphy, and Earth History 1,370 Chronology, proxy archives, ancient environments, long-term planetary evolution, oxygenation, and mass transitions.
5 geomorphology_sediments_surface_processes Geomorphology, Sediments, and Surface Processes 1,280 Landscape evolution, erosion, sediment transport, deposition, weathering, and sediment connectivity.
6 atmosphere_weather_atmospheric_chemistry Atmosphere, Weather, and Atmospheric Chemistry 1,560 Atmospheric dynamics, convection, clouds, precipitation, composition, oxidation capacity, aerosols, and weather predictability.
7 climate_dynamics_feedbacks_predictability_extremes Climate Dynamics, Feedbacks, Predictability, and Extremes 1,980 Climate response, modes of variability, feedbacks, attribution, tipping behavior, and hydroclimatic extremes.
8 cryosphere_permafrost_sea_level Cryosphere, Permafrost, and Sea Level 1,110 Ice sheets, glaciers, snowpack, sea ice, permafrost thaw and carbon, ice shelves, grounding lines, and sea-level components.
9 physical_oceanography_ocean_circulation Physical Oceanography and Ocean Circulation 1,280 Ocean dynamics, diapycnal and mesoscale mixing, internal waves, ventilation, overturning circulation, heat, and freshwater transport.
10 marine_biogeochemistry_seafloor_ocean_ecosystem Marine Biogeochemistry, Seafloor, and Ocean–Ecosystem Coupling 1,280 Ocean carbon biological pump, nutrients, deoxygenation, acidification, trace metals, sediments, hydrothermal exchange, and coupled marine response.
11 hydrology_groundwater_water_cycle Hydrology, Groundwater, and the Water Cycle 1,450 Catchments, rivers, lakes, wetlands, groundwater recharge, aquifer flow, drought propagation, flood generation, and water budgets.
12 soils_critical_zone_terrestrial_biogeochemistry Soils, Critical Zone, and Terrestrial Biogeochemistry 1,280 Soil formation, deep regolith architecture, weathering fronts, soil organic carbon persistence, nutrients, and bedrock-to-canopy coupling.
13 ecosystem_earth_interactions_land_change Ecosystem–Earth Interactions, Land Change, and Environmental Response 1,480 Biosphere–atmosphere feedbacks, disturbance regimes, wildfire dynamics, land-use forcing, ecosystem resilience, and Earth-system consequences.
14 pollution_contaminant_fate_environmental_quality Pollution, Contaminant Fate, and Environmental Quality 1,390 Contaminant sources, geochemical/photochemical transformations, fate and transport, mixtures, persistence, exposure formation, and recovery.
15 coasts_deltas_drylands_urban_coupled_systems Coasts, Deltas, Drylands, Urban Environments, and Coupled Human–Earth Systems 1,100 Boundary environments, delta morphodynamics, land subsidence, urban boundary-layer climate and hydrology, drylands, and compound change.
Total Published 20,000

Problem Sets & Flagship Sources (sets.json)

Set ID Set Slug Name Published Problems Description
1 nasem_earth_in_time_and_decadal_surveys National Academies Decadal Surveys (Earth in Time, Thriving on Our Changing Planet, Forecasting the Ocean) 57 High-priority solid-Earth, surface-Earth, ocean, and Earth-observation science questions from U.S. National Academies consensus studies.
2 iahs_unsolved_problems_in_hydrology IAHS Twenty-Three Unsolved Problems in Hydrology & HELPING Decade 1,458 Community-elicited open problems in catchment hydrology, groundwater, hydroclimatic variability, ecohydrology, and nonstationary water systems.
3 sz4d_iodp_and_solid_earth_frontiers SZ4D, IODP 2050, EarthScope & Solid-Earth Science Frameworks 3,394 Open questions on plate tectonics, mantle geodynamics, subduction fault slip, magmatic drivers of eruptions, subseafloor biosphere, and cascading geohazards.
4 wcrp_wwrp_ipcc_climate_and_atmosphere WCRP, WWRP, IGAC & IPCC AR6 Knowledge Gaps 3,527 Climate sensitivity, cloud-aerosol microphysics, atmospheric oxidation capacity, circulation regimes, extremes attribution, and subseasonal-to-decadal predictability.
5 scar_icarp_cryosphere_and_polar_horizon_scans SCAR Antarctic Horizon Scan, ICARP IV Arctic & Cryosphere Priorities 1,113 Priority questions on ice-sheet grounding-line stability, ice-shelf buttressing, sea-ice dynamics, Southern/Arctic Ocean overturning, and permafrost carbon feedbacks.
6 oceanobs_goos_geotraces_marine_science OceanObs, GOOS 2030, GEOTRACES & Marine Biogeochemistry Syntheses 2,590 Open questions on ocean heat and carbon uptake, diapycnal mixing, trace-metal cycling, biological carbon pump, deoxygenation, and benthic-pelagic coupling.
7 critical_zone_soils_and_geomorphology_syntheses Critical Zone Networks, IUSS Soil Science & Geomorphology Syntheses 2,555 Bedrock-to-canopy weathering fronts, regolith formation, mineral-associated soil organic carbon persistence, sediment connectivity, and landscape evolution.
8 pages_paleoclimate_and_earth_history_archives PAGES, ICS Stratigraphy & Deep-Time Earth History Syntheses 1,367 Geochronology, proxy calibration, Precambrian oxygenation, Phanerozoic mass extinctions, hyperthermals, and Pleistocene glacial-interglacial transitions.
9 unep_ipbes_contaminants_and_coupled_systems UNEP Frontiers, IPBES, Contaminant Fate & Coupled Human–Earth Systems 3,939 Environmental fate and transformation of PFAS, microplastics, trace contaminants, wildfire smoke aging, biosphere-climate feedbacks, deltas, drylands, and urban systems.
10 peer_reviewed_earth_and_environmental_literature Peer-Reviewed Earth & Environmental Review and Research Literature Corpus 0 Explicit open questions and unresolved mechanistic gaps extracted from peer-reviewed Earth and environmental science journals (AGU, EGU, Nature, Science, Elsevier, GSA, AMS, ACS, RSC).

Flagship Tier-A sources include the National Academies (A Vision for NSF Earth Sciences 2020–2030: Earth in Time; Thriving on Our Changing Planet; Forecasting the Ocean: 2025–2035; Volcanic Eruptions and Their Repose: ERUPT), the IAHS Twenty-Three Unsolved Problems in Hydrology (UPH) and HELPING decade synthesis, the SCAR Antarctic and Southern Ocean Science Horizon Scan, the SZ4D Implementation Plan, the 2050 Science Framework for Scientific Ocean Drilling (IODP), WCRP Grand Challenges, IPCC AR6 Working Group I, Critical Zone Collaborative Network syntheses, GEOTRACES, GO2NE, the Permafrost Carbon Network, and PAGES paleoclimate syntheses, paired with strictly vetted open-problem formulations from peer-reviewed Earth and environmental science journals.


Compact Problem Record Schema (problems.json)

Every record in problems.json contains strictly the problem formulations, formal governing equations, Earth-system taxonomy, knowledge-graph links, scientific context, and peer-reviewed reference citations needed to state and verify the problem:

  • id, problem_number, title
  • statement (canonical research question), plain_statement (accessible formulation), precise_statement (mechanistic/boundary-value formulation with embedded LaTeX governing equation)
  • category, category_id, category_name, subdiscipline, set_id, question_types
  • earth_system_components, environmental_media, processes
  • spatial_scale, region, temporal_scale, geologic_era
  • observables (directly measured quantities), inferred_properties (latent states/fluxes inferred via inversion or modeling), & governing_relations (2 formal LaTeX governing equations / dimensionless groups for the sub-discipline)
  • background (literature context and why the question remains open) & what_would_settle_it (decisive observations, experiments, or coupled model breakthroughs)
  • status (open, partially_solved, or archived solved/premise_rejected/not_well_posed), consensus_state, research_classification, published
  • difficulty, difficulty_level, origin_year, proposed_by, literature_checked_at
  • related_problems (Cross-Problem Knowledge Graph: 3 linked UEARTH-* problem IDs — 2 within-subdiscipline + 1 cross-category coupled problem)
  • reference_dois (list of 4 peer-reviewed DOIs) & references (4 formatted citations per published problem)

Mandatory Dataset Warnings & Responsible Use

Status Is Time-Indexed: Every status classification (open, partially_solved, solved, premise_rejected) is a time-stamped literature judgment (literature_checked_at = "2026-10-16"), not a timeless truth. New field campaigns, satellite missions, drilling expeditions, or theoretical breakthroughs may shift a problem's status.

Paraphrased Formulations Are Normalized: Problem statements (statement, plain_statement, precise_statement) are structured scientific paraphrases rather than verbatim publisher quotations, and no raw paper texts are stored in the repository. Consult the cited peer-reviewed sources via reference_dois and references when exact historical wording matters.

Earth & Geohazard Problems Are Not Operational Forecasts or Safety Advice: Records in Category 2 (earthquakes, volcanoes, tsunamis, landslides), Category 6/7 (extreme weather/climate), Category 11 (floods/droughts), and Category 14 (contaminants) describe fundamental research questions and must never be used as operational hazard warnings, site-safety clearances, or clinical/drinking-water guidance.


Sample Flagship Problems

UEARTH-000001 — Nonstationarity of the Hydrological Cycle Under Climate and Environmental Change (UPH 1)

  • Category: hydrology_groundwater_water_cycle (Hydrology, Groundwater, and the Water Cycle) | Sub-Discipline: catchment_runoff_transit_time_uph
  • Status: open (multiple_viable_hypotheses) | Difficulty: hard (Level 4)
  • Canonical Question (statement): Is the terrestrial hydrological cycle regionally accelerating or decelerating under coupled climate and environmental change, and are there abrupt tipping thresholds in catchment water balance partitioning?
  • Plain Question (plain_statement): Is the water cycle speeding up or slowing down across different regions as climate and land use change, and does it have tipping points?
  • Precise Formulation (precise_statement): Across major hydroclimatic regimes and multi-decadal instrumental records, how do radiative forcing, atmospheric evaporative demand, and land-cover change alter catchment-scale precipitation-runoff-evapotranspiration partitioning ($P - E - Q = \Delta S$), and under what boundary conditions does nonlinear storage-discharge feedback induce hysteresis or regime shifts?
  • Governing Relations (governing_relations): Kirchner dynamical catchment storage-discharge sensitivity $g(Q) = dQ/dS = (-dQ/dt) / (Q - P + E)$ and power-law recession $-dQ/dt = a Q^b$; master transit-time StorAge Selection (SAS) transport $\partial_t S_T(T, t) + \partial_T S_T(T, t) = J(t) - Q(t) \Omega_Q(S_T, t) - E(t) \Omega_E(S_T, t)$
  • Observables: high-frequency stream and precipitation stable water isotopes (delta-18O, delta-2H), electrical conductivity, and discharge, nested hillslope tensiometer/piezometer networks and StorAge Selection (SAS) transit-time distributions
  • Inferred Properties: emergent catchment-scale storage-discharge constitutive relations from heterogeneous hillslope preferential flow
  • Linked Problems (related_problems): UEARTH-013460, UEARTH-000015, UEARTH-019411
  • Peer-Reviewed References (references):
    • Twenty-three unsolved problems in hydrology (UPH) - a community perspective (2019), Time Variability and Change (UPH 1), DOI:10.1080/02626667.2019.1620507
    • Jha et al. (2026), H2Open Journal, DOI:10.1016/j.htopen.2026.100092
    • Tanner et al. (2015), Hydrological Sciences Journal, DOI:10.1080/02626667.2015.1052453
    • B. Arheimer, C. Cudennec, A. Castellarin et al. (2024), The IAHS Science for Solutions decade (HELPING), Hydrological Sciences Journal 69(11), 1417-1435.

UEARTH-001201 — Geochemical Characteristics and Significance of Molecular Markers in the Paleogene-Neogene Crude Oils of the Northwest Qaidam Basin

  • Category: deep_earth_tectonics_geodynamics_geomagnetism (Deep Earth, Tectonics, Geodynamics, and Geomagnetism) | Sub-Discipline: craton_orogen_continental_crust
  • Status: open (multiple_viable_hypotheses) | Difficulty: hard (Level 4)
  • Canonical Question (statement): How can the regional distribution characteristics of molecular markers of crude oil and the petroleum system elements relevant to the distribution of oil and gas in the northwest Qaidam Basin be quantitatively constrained across Himalaya–Tibetan Plateau and Central Asian Orogenic System, and what is the relative importance of crustal deformation versus metamorphic transformation?
  • Plain Question (plain_statement): How do crustal deformation and crystalline rock properties work together to govern geochemical characteristics and significance of molecular markers in the Paleogene-Neogene crude oils of the northwest Qaidam Basin across Himalaya–Tibetan Plateau and Central Asian Orogenic System?
  • Precise Formulation (precise_statement): Within crystalline rock of the continental crust (0–200 km), how do continental collision, lithospheric thickening, and convective removal of eclogitized lower crust and Moho temperature, crustal radiogenic heat production, and cratonic keel composition interact via crustal deformation (governed by viscous thin-sheet Argand number $\mathrm{Ar} = g \rho_c (1 - \rho_c/\rho_m) H_c^2 / (\eta_{\mathrm{eff}} U_0)$) to control geochemical characteristics and significance of molecular markers in the Paleogene-Neogene crude oils of the northwest Qaidam Basin, and can crustal receiver-function Moho depth maps, Bouguer gravity anomalies, and xenolith thermobarometry uniquely resolve secular continental crust growth versus recycling rates and lower-crustal foundry mechanics?
  • Governing Relations (governing_relations): viscous thin-sheet Argand number $\mathrm{Ar} = g \rho_c (1 - \rho_c/\rho_m) H_c^2 / (\eta_{\mathrm{eff}} U_0)$; isopycnic cratonic root stability $\Delta \rho(T, X_{\mathrm{Mg#}}) = \rho_0 [ -\alpha (T - T_0) + \beta_{\mathrm{chem}} \Delta X_{\mathrm{Mg#}} ] \approx 0$
  • Observables: crustal receiver-function Moho depth maps, Bouguer gravity anomalies, and xenolith thermobarometry, zircon U-Pb/Hf-O isotopic arrays and whole-rock major/trace-element crustal compilations
  • Inferred Properties: secular continental crust growth versus recycling rates and lower-crustal foundry mechanics
  • Linked Problems (related_problems): UEARTH-000631, UEARTH-000370, UEARTH-001584
  • Peer-Reviewed References (references):
    • Meng et al. (2024), ACS omega, DOI:10.1021/acsomega.4c05687
    • Behera et al. (2024), Environmental research, DOI:10.1016/j.envres.2024.118909
    • Zhang et al. (2024), Scientific reports, DOI:10.1038/s41598-024-79190-9
    • NASEM (2020), A Vision for NSF Earth Sciences 2020-2030: Earth in Time (Solid Earth & Geodynamics Synthesis), National Academies Press.

UEARTH-005015 — A standardised classification scheme for the Mid-Holocene Toalean artefacts of South Sulawesi, Indonesia

  • Category: geologic_time_paleoclimate_stratigraphy_earth_history (Geologic Time, Paleoclimate, Stratigraphy, and Earth History) | Sub-Discipline: quaternary_orbital_ice_core_paleoclimate
  • Status: open (framework_dependent) | Difficulty: hard (Level 4)
  • Canonical Question (statement): How do coupled processes of radiative transfer and energy balance and carbon cycle and biogeochemical cycling in ice or snow control A standardised classification scheme for the mid-Holocene toalean artefacts of South Sulawesi, indonesia across Humid Tropical River Basins and Maritime Continent, and how can ice-core trapped-gas CO2/CH4 records, speleothem U-Th/delta-18O series, and loess-paleosol sequences resolve interhemispheric phasing of millennial abrupt climate oscillations and deep-ocean carbon storage?
  • Plain Question (plain_statement): How do radiative transfer and energy balance and ice or snow properties work together to govern A standardised classification scheme for the mid-Holocene toalean artefacts of South Sulawesi, indonesia across Humid Tropical River Basins and Maritime Continent?
  • Precise Formulation (precise_statement): Within ice or snow of the sedimentary stratigraphic archive (Surface to 4 km ice/sediment depth), how do Milankovitch orbital insolation variations, ice-sheet albedo feedbacks, and AMOC reorganizations and continental ice-sheet geometry, Southern Ocean sea-ice extent, and dust radiative forcing interact via radiative transfer and energy balance (governed by bipolar seesaw heat balance $C_S dT_S/dt = -\Delta Q_{\mathrm{AMOC}}(t) - \lambda_S T_S$) to control A standardised classification scheme for the mid-Holocene toalean artefacts of South Sulawesi, indonesia, and can ice-core trapped-gas CO2/CH4 records, speleothem U-Th/delta-18O series, and loess-paleosol sequences uniquely resolve interhemispheric phasing of millennial abrupt climate oscillations and deep-ocean carbon storage?
  • Governing Relations (governing_relations): Milankovitch insolation-forced ice volume $dV_{\mathrm{ice}}/dt = I(65^\circ\mathrm{N}, e, \varepsilon, \varpi) - V_{\mathrm{ice}}/\tau_{\mathrm{ablation}}(p\mathrm{CO}2)$; bipolar seesaw heat balance $C_S dT_S/dt = -\Delta Q{\mathrm{AMOC}}(t) - \lambda_S T_S$
  • Observables: ice-core trapped-gas CO2/CH4 records, speleothem U-Th/delta-18O series, and loess-paleosol sequences, marine benthic foraminiferal delta-18O/delta-13C stacks and alkenone/TEX86 sea-surface temperatures
  • Inferred Properties: interhemispheric phasing of millennial abrupt climate oscillations and deep-ocean carbon storage
  • Linked Problems (related_problems): UEARTH-004925, UEARTH-004931, UEARTH-007951
  • Peer-Reviewed References (references):
    • Perston et al. (2021), PloS one, DOI:10.1371/journal.pone.0251138
    • Wang et al. (2025), PloS one, DOI:10.1371/journal.pone.0327224
    • Gruwier et al. (2023), American Journal of Biological Anthropology, DOI:10.1002/ajpa.24840
    • J. E. Tierney, C. J. Poulsen, I. P. Montañez et al. (2020), Past climates inform our future, Science 370(6517), eaay3701.

UEARTH-012641 — Effects of hull cleaning wastewater on coastal plankton community: A mesocosm experiment

  • Category: marine_biogeochemistry_seafloor_ocean_ecosystem (Marine Biogeochemistry, Seafloor, and Ocean-Ecosystem Coupling) | Sub-Discipline: biological_carbon_pump_export_phytoplankton
  • Status: partially_solved (mechanism_known_magnitude_uncertain) | Difficulty: medium (Level 3)
  • Canonical Question (statement): What physical, chemical, and dynamical mechanisms govern the contaminants can directly alter water of effects of hull cleaning wastewater on coastal plankton community regarding A mesocosm experimentchemistry and disrupt planktonic community dynamics, yet their ecological effects in coastal environments, and how do euphotic-zone nutrient supply, mixed-layer light availability, and ocean warming stratification interact with phytoplankton community size structure, mineral ballast (opal/CaCO3) ratios, and mesopelagic temperature?
  • Plain Question (plain_statement): What natural processes control effects of hull cleaning wastewater on coastal plankton community regarding A mesocosm experiment in Earth's open ocean, and how does it respond to euphotic-zone nutrient supply, mixed-layer light availability, and ocean warming stratification?
  • Precise Formulation (precise_statement): Within seawater of the open ocean (0–1,000 m (epipelagic to mesopelagic)), how do euphotic-zone nutrient supply, mixed-layer light availability, and ocean warming stratification and phytoplankton community size structure, mineral ballast (opal/CaCO3) ratios, and mesopelagic temperature interact via carbon cycle and biogeochemical cycling (governed by Sverdrup-Behrenfeld phytoplankton net growth $dP/dt = [\mu(I, T, \mathrm{N, Fe}) - m_{\mathrm{graz}}(Z) - w_s/h_m] P$) to control effects of hull cleaning wastewater on coastal plankton community regarding A mesocosm experiment, and can BGC-Argo bio-optical/nitrate/oxygen floats, neutrally buoyant sediment traps, and Underwater Vision Profilers (UVP) uniquely resolve microbial remineralization vs. mineral-ballast protection controlling twilight-zone transfer efficiency?
  • Governing Relations (governing_relations): Martin power-law POC flux attenuation $F_{\mathrm{POC}}(z) = F_{\mathrm{POC}}(z_0) (z / z_0)^{-b(T, [\mathrm{O}2])}$ where $b = k{\mathrm{remin}}(T) / w_{\mathrm{sink}}$; Sverdrup-Behrenfeld phytoplankton net growth $dP/dt = [\mu(I, T, \mathrm{N, Fe}) - m_{\mathrm{graz}}(Z) - w_s/h_m] P$
  • Observables: BGC-Argo bio-optical/nitrate/oxygen floats, neutrally buoyant sediment traps, and Underwater Vision Profilers (UVP), 234Th/238U disequilibrium export fluxes and satellite hyperspectral ocean-color phytoplankton functional types
  • Inferred Properties: microbial remineralization vs. mineral-ballast protection controlling twilight-zone transfer efficiency
  • Linked Problems (related_problems): UEARTH-012137, UEARTH-012161, UEARTH-010867
  • Peer-Reviewed References (references):
    • Lee et al. (2025), Journal of hazardous materials, DOI:10.1016/j.jhazmat.2025.139458
    • Antoni et al. (2025), Frontiers in microbiomes, DOI:10.3389/frmbi.2025.1659695
    • Zhu et al. (2026), Water research, DOI:10.1016/j.watres.2025.125134
    • D. Breitburg, L. A. Levin, A. Oschlies et al. (2018), Declining oxygen in the global ocean and coastal waters, Science 359(6371), eaam7240.

UEARTH-018901 — Educating for environmental transition: the summer school on microplastics

  • Category: pollution_contaminant_fate_environmental_quality (Pollution, Contaminant Fate, and Environmental Quality) | Sub-Discipline: microplastics_nanoplastics_weathering_vectors
  • Status: open (framework_dependent) | Difficulty: medium (Level 3)
  • Canonical Question (statement): In the context of educating for environmental transition regarding the summer school on microplastics, what mechanisms govern challenges in scientific monitoring, policymaking, and public engagement, and how is it modulated by polymer crystallinity/density, suspended mineral floc concentration, and estuarine salinity fronts?
  • Plain Question (plain_statement): What natural processes control challenges in scientific monitoring, policymaking, and public engagement in relation to educating for environmental transition regarding the summer school on microplastics?
  • Precise Formulation (precise_statement): Within freshwater surface of the river (Surface waters to deep-sea benthic sediments), how do solar UV irradiance, hydrodynamic shear fragmentation, and microbial biofouling succession and polymer crystallinity/density, suspended mineral floc concentration, and estuarine salinity fronts interact via contaminant transport and fate (governed by shape-dependent Dietrich settling velocity $w_s^* = f(D^*, \mathrm{CSF}, P_{\mathrm{roundness}}, \rho_p(\text{biofilm}) - \rho_w)$) to control educating for environmental transition regarding the summer school on microplastics, and can micro-FTIR, micro-Raman, and pyrolysis-GC-MS polymer quantification down to sub-micron nanoplastic scales uniquely resolve biofilm heteroaggregation ('plastisphere') altering buoyancy, vertical settling velocities, and co-contaminant/AMR vectoring?
  • Governing Relations (governing_relations): DLVO colloidal attachment-detachment transport $\partial_t C + v \partial_x C - D \partial_{xx} C = -k_{\mathrm{att}}(\Phi_{\mathrm{DLVO}}, I) \psi_{\mathrm{block}} C + k_{\mathrm{det}} \rho_b S / \theta$; shape-dependent Dietrich settling velocity $w_s^* = f(D^*, \mathrm{CSF}, P_{\mathrm{roundness}}, \rho_p(\text{biofilm}) - \rho_w)$
  • Observables: micro-FTIR, micro-Raman, and pyrolysis-GC-MS polymer quantification down to sub-micron nanoplastic scales, settling-column biofouling experiments and dated sediment-core microplastic accumulation profiles
  • Inferred Properties: biofilm heteroaggregation ('plastisphere') altering buoyancy, vertical settling velocities, and co-contaminant/AMR vectoring
  • Linked Problems (related_problems): UEARTH-017560, UEARTH-017659, UEARTH-013429
  • Peer-Reviewed References (references):
    • Slaveykova et al. (2026), Environmental science and pollution research international, DOI:10.1007/s11356-025-37253-y
    • Wu et al. (2026), Environmental science & technology, DOI:10.1021/acs.est.6c00432
    • Jeffries et al. (2025), ACS Food Science & Technology, DOI:10.1021/acsfoodscitech.4c01093
    • M. G. Evich, M. J. B. Davis, J. P. McCord et al. (2022), Per- and polyfluoroalkyl substances in the environment, Science 375(6580), eabg9065.

Compact Repository Structure

unsolvedearth/
├── README.md                  # Main overview & Hugging Face Dataset Card
├── DATASET_CARD.md            # Detailed dataset card & methodology
├── CHANGELOG.md               # Release history (v1.0.0 -> v1.1.0)
├── LICENSE                    # CC-BY-4.0 license
├── CITATION.cff               # Citation metadata
├── problems.json              # All 20,100 records (20,000 published + 100 archived)
├── categories.json            # 15 primary Earth & environmental categories
├── difficulty_levels.json     # Difficulty scale (Levels 1-5) & dimensions
├── sets.json                  # 10 curated problem sets / source families
├── statistics.json            # Summary counts, category breakdown & literature stats
├── schemas/                   # JSON Schemas (Draft 2020-12)
├── taxonomy/                  # 10 controlled vocabulary YAML files
├── scripts/                   # Harvesting, assembly & validation scripts
└── docs/                      # Scope, status, rights & governance guides

Quickstart Usage in Python

import json
from datasets import load_dataset

# Load directly via Hugging Face datasets
ds = load_dataset("ulamai/UnsolvedEarth", split="train")
published = [p for p in ds if p["published"]]
print(f"Published open/partial problems: {len(published):,}")

# Filter by primary category and status
hydro_open = [
    p for p in published
    if p["category"] == "hydrology_groundwater_water_cycle"
    and p["status"] == "open"
]
print(f"Open Hydrology problems: {len(hydro_open):,}")
print("Sample:", hydro_open[0]["id"], "->", hydro_open[0]["statement"])
print("References:", hydro_open[0]["references"])
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