bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of irrigation expansion on historical climate change during the last 115 years: insights from CMIP6
Authors: Al-Yaari Amen , Ducharne Agnes , Thiery Wim , Cheruy Frederique , Lawrence David
Published: March 2021

Irrigated areas have increased, faster than the growth of the world population, from around 0.63 million km2 at the start of the 20th century to 3.1 million km2 of land in 2005, that is five times of area in 1900 (0.6 million km2). Irrigation is one of the land management practices with the largest biogeochemical and biogeophysical effects on climate. However, incorporating land management factors (including irrigation) into most of the state‐of‐the‐art climate models under the Coupled Model Intercomparison Project, Phase 6 (CMIP6) coordinated by the World Climate Research Programme (WCRP) is still overlooked. To our best knowledge, three models, however, take into account irrigation activities: namely NorESM2‐LM, GISS‐E2‐H, and CESM2. The overall objective of the study is to investigate the role of irrigation on climate change at the global scale by looking at temporal trends of Essential Climate variables (ECVs) that characterize the Earth's climate (Evapotranspiration, leaf area index, precipitation, soil moisture, radiation, and air temperature) over the last 115 years (i.e. 1900-2014). Within this investigation, we compared models with irrigation vs. models without irrigation using 20 models from different CMIP6 experiments: coupled land-atmosphere amip (observed sea surface temperatures and sea ice concentrations), coupled land-atmosphere-ocean historical simulation, and offline land-hist (land only simulations). Temporal trends over the 1900-2014 period were computed then spatially binned by the "FAO Global Map of Irrigation Areas", which represents area equipped for irrigation expressed as percentage of total area around the year 2005. For the three CMIP6 experiments, the three models with irrigation switched on showed similar and distinguished behavior from all other models with irrigation switched off over intensively irrigated areas: mean annual evapotranspiration and soil moisture increased over time (positive trends vs. negative or no trends for all other none-irrigation models). This increase in evapotranspiration over time was reflected in the negative trends (i.e. cooling) of annual maximum air temperature for the irrigation models vs. positive trends for most of the none-irrigation models. The ET temporal positive trends over intensively irrigated areas were detected and confirmed by four different satellite-based ET products. The consistent results among the three experiments and confirmed by different satellite data imply the importance of incorporating anthropogenic factors in the next generation of climate models.
Inferring precipitation from atmospheric general circulation model variables
Authors: Hess Philipp , Boers Niklas
Published: March 2021

The accurate prediction of precipitation, in particular of extremes, remains a challenge for numerical weather prediction (NWP) models. A large source of error are subgrid-scale parameterizations of processes that play a crucial role in the complex, multi-scale dynamics of precipitation, but are not explicitly resolved in the model formulation. Recent progress in purely data-driven deep learning for regional precipitation nowcasting [1] and global medium-range forecasting [2] tasks has shown competitive results to traditional NWP models.
Here we follow a hybrid approach, in which explicitly resolved atmospheric variables are forecast in time by a general circulation model (GCM) ensemble and then mapped to precipitation using a deep convolutional autoencoder. A frequency-based weighting of the loss function is introduced to improve the learning with regard to extreme values.
Our method is validated against a state-of-the-art GCM ensemble using three-hourly high resolution data. The results show an improved representation of extreme precipitation frequencies, as well as comparable error and correlation statistics.
   

[1] C.K. Sønderby et al. "MetNet: A Neural Weather Model for Precipitation Forecasting." arXiv preprint arXiv:2003.12140 (2020). 
[2] S. Rasp and N. Thuerey "Purely data-driven medium-range weather forecasting achieves comparable skill to physical models at similar resolution." arXiv preprint arXiv:2008.08626 (2020).
How do transitions affect the wave overtopping flow locally as well as downstream?
Authors: van Bergeijk Vera , Warmink Jord , Hulscher Suzanne
Published: March 2021

Wave overtopping on grass-covered dikes results in erosion of the dike cover. Once the dike cover is eroded, the core will be washed away and the dike breaches, leading to flooding of the hinterland. Transitions between grass covers and revetments or geometric transitions are vulnerable for cover erosion and are therefore the most likely locations to initiate dike breach. These transitions affect the overtopping flow and thereby the hydraulic load on the dike cover. For example, bed roughness differences can create additional turbulence and slope changes can result in the formation of a jet that increases the load at the jet impact location. Although it is known that dike cover failure often starts at transitions, the effect of transitions on the hydraulic load remains unknown.

We developed a detailed numerical 2DV model in OpenFOAM for the overtopping flow over the crest and the landward slope of a grass-covered dike. This model is used to study the effects of transitions on the overtopping flow variables including the flow velocity, shear stress, normal stress and pressure. Several types of transitions are studied such as revetment transitions, slope changes and height differences. 

The results show that the shear stress, normal stress and pressure increase significantly at geometric transitions such as the transition from the crest to the slope and at the landward toe. The increase depends on the wave volume and the geometry of the dike such as the steepness and length of the landward slope. Furthermore, the results show that roughness changes at revetment transition on a grass-covered crest has no influence on the maximum shear stress, maximum normal stress and maximum pressure. The flow velocity increases from a rough to a smooth revetment, while the opposite occurs for the transition from a smooth to a rough revetment. The variation in the flow velocity is well described by analytical formulas for the maximum flow velocity along the dike profile. These formulas are also able to describe the variation in flow velocity for a revetment transition on a berm on the landward slope. In this case, the shear stress increases from a smooth to a rough revetment and decreases from a rough to a smooth revetment. This means that a rough revetment can locally reduce the shear stress, however the transitions have no effect on the shear stress downstream.

These model results are used to obtain relations for the increase in the hydraulic variables at transitions. These relations can be used to describe the effect of transitions on the hydraulic load in models for grass cover failure by overtopping waves. Accurate descriptions of the hydraulic load in these models will improve the failure assessment of grass-covered dikes with transitions.
Seasonal weather forecasts as a decision support tool in the Douro Wine Region, Portugal
Authors: Santos João Andrade , Ceglar Andrej , Toreti Andrea , Prodhomme Chloé
Published: March 2021

Weather conditions in a given year largely control wine production, despite all the mitigation measures that can be undertaken in the vineyards and wineries. As such, seasonal weather forecasts can be a valuable decision support tool for assisting winemakers in short to medium-term management, particularly when coupled with wine production models. Adequate and timely agricultural management grounded on predicted wine production will reduce the risks and enhance the efficiency of the sector. In this study, the performance of seasonal weather forecasts of wine production in the Portuguese Douro & Port wine region (D&P WR) is evaluated. However, this concept can be extended to other wine regions worldwide. A predictive logistic model of wine production is developed herein. Monthly mean air temperatures and monthly total precipitation, averaged over the periods of February–March, May–June, and July–September, and an autoregressive component of wine production are taken into account for this purpose. The wine production time series for the D&P WR and over the period 1950–2017 (68 years) is categorized into three classes based on quantiles: high, normal and low production years. The empirical wine production model reveals a correct estimation ratio of nearly 2/3 when applied to independent 10%-random subsamples taken from the complete time series. The performance of the ECMWF 7-month seasonal weather forecasts (issued from February to August) to predict the temperature and precipitation variables used in the wine production model is subsequently assessed. The results show a reasonable performance in predicting these variables. Furthermore, the forecasts from May to August are clearly the best performing, as 1) more observed data is included in the empirical wine production model, and 2) the performance of seasonal forecasts for summer months is higher, owing to the local Mediterranean-type climate characteristics, with typically dry and settled atmospheric conditions in summer. The extension of this approach to other wine regions in Europe, as well as its operational application, are foreseen in the near future within the framework of the European Commission-funded action “Climate change impact mitigation for European viticulture: knowledge transfer for an integrated approach – Clim4Vitis” [grant number 810176].
Occurrence and origin of polonium-210 in a sandstone aquifer in Germany
Authors: Hofmann Peggy , Wagner Frank , Lucks Christian , Wittwer Christiane
Published: March 2021

Polonium-210 (Po-210) is a naturally occurring high-energy alpha emitter with a high dose coefficient compared to other natural radionuclides. In groundwater, Po-210 concentrations usually are low due to its high surface reactivity and tendency to readily adsorb onto mineral surfaces. The nationwide median in drinking water in Germany is 1.4 mBq/L as shown by investigations of the Federal Office for Radiation Protection (BfS). However, some sites in southern Sachsen-Anhalt in Germany were revealed to have Po‑210 activity concentrations far above 100 mBq/L. This is of particular relevance, since the EU Council Directive 2013/51/Euratom and its national implementation in the German Drinking Water Ordinance specifies requirements for drinking water quality with regard to artificial and natural radioactive substances. These high values of Po-210 would require reduction measures according to legislation.  

In order to gain a better understanding of the occurrence and origin of Po-210 in groundwater, further groundwater wells and water supply facilities in southern Sachsen-Anhalt were selected for analysis, taking into account the regional geology. The investigated aquifers pertain to the rock sequences of the Lower, Middle and Upper Buntsandstein (Lower Triassic), the Lower Muschelkalk (Middle Triassic) and Cenozoic stratigraphic units. Unfiltered water samples from 50 sites in total were analyzed for their content of natural radionuclides, major and trace elements as well as their oxygen and hydrogen isotope composition and supplemented by the examination of drill core material from these rock sequences.

The data indicate that the elevated Po-210 activity concentrations are limited to the aquifer of the Middle Buntsandstein. The simultaneous absence of the parent nuclides lead-210 (Pb-210) and radon-222 in the water samples indicate a local release mechanism in the rock. In the Middle Buntsandstein the amount of Pb-210 would be sufficient to provide the amount of Po-210 found in solution and the available clay minerals like illite, chlorite, hematite and muscovite could serve as potential hosts for Pb-210 and Po-210. Redox-indicators and a relatively high content of dissolved organic material (DOC >1 mg/L) found in the water samples of the Middle Buntsandstein aquifer could be interpreted as an indication of microbially induced reduction processes.

Understanding the geochemical processes responsible for the mobilization of Po-210 could provide necessary information helping to minimize the human exposure caused by drinking water consumption. Therefore, further investigations will focus on the size distribution of Po-210-bearing particles, the presence of the short-lived mother nuclide bismuth-210 and the sulfate isotope distribution at selected Po-210-rich groundwater sites in this study area.
Downscaling seismic tomography models
Authors: Hedjazian Navid , Bodin Thomas , Capdeville Yann
Published: March 2021

Seismic imaging techniques such as elastic full waveform inversion (FWI) have their spatial resolution limited by the maximum frequency present in the observed waveforms. Scales smaller than a fraction of the minimum wavelength cannot be resolved, only a smoothed version of the true underlying medium can be recovered. Application of FWI to media containing small and strong heterogeneities therefore remains problematic. This smooth tomographic image is related to the effective elastic properties, which can be exposed with the homogenization theory of wave propagation. We study how this theory can be used in the FWI context. The seismic imaging problem is broken down in a two-stage multiscale approach. In the first step, called homogenized full waveform inversion (HFWI), observed waveforms are inverted for a macro-scale, fully anisotropic effective medium, smooth at the scale of the shortest wavelength present in the wavefield. The solution being an effective medium, it is difficult to directly interpret it. It requires a second step, called downscaling, where the macro-scale image is used as data, and the goal is to recover micro-scale parameters. All the information contained in the waveforms is extracted in the HFWI step. The solution of the downscaling step is highly non-unique as many fine-scale models may share the same long wavelength effective properties. We therefore rely on the introduction of external a priori information. In this step, the forward theory is the homogenization itself. It is computationally cheap, allowing to consider geological models with more complexity.

In a first approach to downscaling, the ensemble of potential fine-scale models is described with an object-based parametrization, and explored with a MCMC algorithm. We illustrate the method with a synthetic cavity detection problem. In a second approach, the prior information is introduced by the means of a training image, and the fine-scale model is recovered with a multi-point statistics algorithm. We apply this method on a subsurface synthetic problem, where the goal is to recover geological facies.

 
The impact of shallow stratification on air-sea CO2 flux in the summer Arctic Ocean
Authors: Dong Yuanxu , Bakker Dorothee , Bell Thomas , Liss Peter , Brown Ian , Kitidis Vassilis , Yang Mingxi
Published: March 2021

Air-sea carbon dioxide (CO2) flux is often indirectly estimated by the bulk method using the in-situ air-sea difference in CO2 fugacity and a wind speed dependent parameterisation of the gas transfer velocity (K). In the summer, sea-ice melt in the Arctic Ocean generates strong shallow stratification with significant gradients in temperature, salinity, dissolved inorganic carbon (DIC) and alkalinity (TA), and thus a near-surface CO2 fugacity  (fCO2w) gradient. This gradient can cause an error in bulk air-sea CO2 flux estimates when the fCO2w is measured by the ship’s underway system at ~5 m depth. Direct air-sea CO2 flux measurement by eddy covariance (EC) is free from the impact of shallow stratification because the EC CO2 flux does not rely on a fCO2w measurement. In this study, we use summertime EC flux measurements from the Arctic Ocean to back-calculate the sea surface fCO2w and temperature and compare them with the underway measurements. We show that the EC air-sea CO2 flux agrees well with the bulk flux in areas less likely to be influenced by ice melt (salinity > 32). However, in regions with salinity less than 32, the underway fCO2w is higher than the EC estimate of surface fCO2w and thus the bulk estimate of ocean CO2 uptake is underestimated. The fCO2w difference can be partly explained by the surface to sub-surface temperature difference. The EC estimate of surface temperature is lower than the sub-surface water temperature and this difference is wind speed-dependent. Upper-ocean salinity gradients from CTD profiles suggest likely difference in DIC and TA concentrations between the surface and sub-surface water. These DIC and TA gradients likely explain much of the near-surface fCO2w gradient. Accelerating summertime loss of sea ice results in additional meltwater, which enhances near-surface stratification and increases the uncertainty of bulk air-sea CO2 flux estimates in polar regions.
Complex kinematics in a major ductile shear zone, NW Shetland: Evidence of ductile extrusion during Caledonian transpression
Authors: Armitage Timothy , Holdsworth Robert , Strachan Robin , Zach Thomas , Alvarez-Ruiz Diana , Dempsey Eddie
Published: March 2021

Ductile shear zones are heterogeneous areas of strain localisation which often display variation in strain geometry and combinations of coaxial and non-coaxial deformation. One such heterogeneous shear zone is the c. 2 km thick Uyea Shear Zone (USZ) in northwest Mainland Shetland (UK), which separates variably deformed Neoarchaean orthogneisses in its footwall from Neoproterozoic metasediments in its hanging wall (Fig. a). The USZ is characterised by decimetre-scale layers of dip-slip thrusting and extension, strike-slip sinistral and dextral shear senses and interleaved ultramylonitic coaxially deformed horizons. Within the zones of transition between shear sense layers, mineral lineations swing from foliation down-dip to foliation-parallel in kinematically compatible, anticlockwise/clockwise-rotations on a local and regional scale (Fig. b). Rb-Sr dating of white mica grains via laser ablation indicates a c. 440-425 Ma Caledonian age for dip-slip and strike-slip layers and an 800 Ma Neoproterozoic age for coaxial layers. Quartz opening angles and microstructures suggest an upper-greenschist to lower-amphibolite facies temperature for deformation. We propose that a Neoproterozoic, coaxial event is overprinted by Caledonian sinistral transpression under upper greenschist/lower amphibolite facies conditions. Interleaved kinematics and mineral lineation swings are attributed to result from differential flow rates resulting in vertical and lateral extrusion and indicate regional-scale sinistral transpression during the Caledonian orogeny in NW Shetland. This study highlights the importance of linking geochronology to microstructures in a poly-deformed terrane and is a rare example of a highly heterogeneous shear zone in which both vertical and lateral extrusion occurred during transpression.
The Art of Identifying Equatorial Waves
Authors: Knippertz Peter , Dias Juliana , Fink Andreas H. , Gehne Maria , Kiladis George , Kikuchi Kazuyoshi , Methven John , Rasheeda Satheesh Athul , Roundy Paul E. , Schlueter Andreas , Wheeler Matthew C. , Woolnough Steven J. , Yang Gui-Ying , Žagar Nedjeljka
Published: March 2021

Equatorial waves are synoptic- to planetary-scale propagating disturbances at low latitudes with frequencies from a few days to several weeks. Here this term includes Kelvin waves, equatorial Rossby waves, mixed-Rossby gravity waves, and inertio-gravity waves, which are closely related to linear wave theory, but also tropical disturbances, African easterly waves, and the intraseasonal Madden-Julian Oscillation. These waves can couple with deep convection, leading to a substantial modulation of rainfall. Recent work has shown that equatorial waves are amongst the dynamical features internal to the troposphere with the longest intrinsic predictability and that some models forecast them with an exploitable level of skill at lead times of up to a few weeks.

A number of methods have been developed to identify and objectively isolate equatorial waves, both in (usually satellite) observations and in model fields. Most of these rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations or shallow water system on the tropical beta plane. Common ingredients to these methods are longitude-time filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper aims to give an overview of the different methods to isolate the waves and their structures, to discuss underlying assumptions, to provide a systematic comparison, and to reveal advantages and disadvantages of each method. This way this study helps to optimally choose an approach suited to a given problem at hand and to avoid misuse and misinterpretation of the results.
A policy tree optimization approach to dynamic adaptation under climate uncertainty
Authors: Herman Jonathan , Cohen Jonathan
Published: March 2021

Water resources systems face a wide range of uncertainty in future hydroclimatic and socio-economic conditions, justifying an adaptive planning approach. Recent advances in dynamic adaptation have designed policies in which infrastructure and management actions are triggered by thresholds of indicator variables monitored over time. Typically, one or more of these components are prespecified, constraining the flexibility of policy design and evaluation. The opportunity exists for methods to identify policies combining the most relevant indicators, actions, and thresholds for dynamic adaptation to climate change. Here we present a generalized framework based on multi-objective policy tree optimization, a heuristic policy search method in which adaptation policies are represented as binary trees. We demonstrate this approach using an illustrative water resources planning problem in California where infrastructure expansion, reservoir operations, conservation rules, and conjunctive use are adapted over time to balance flood risk, water supply, and environmental objectives. To capture the uncertainty in nonstationary forcing, indicator variables include long-term hydroclimatic statistics from downscaled GCM projections along with uncertain land use and economic conditions. Policy robustness is determined by validation against a held-out scenario ensemble. A key focus of the results is comparing the indicators and actions selected by robust versus non-robust policies to identify cases where policies adapt to a signal rather than noise. This framework is supported by open source software and is generalizable across water resources systems challenged with adaptive planning under climate uncertainty.
Early Methane Mitigation Critical to Preserving Arctic Summer Sea Ice
Authors: Sun Tianyi , Ocko Ilissa , Hamburg Steven
Published: March 2021

Methane mitigation is a key component of limiting the extent of global warming. However, little is known about how methane mitigation can benefit other critical aspects of the climate system, such as tipping elements. This study explores how reducing methane emissions can avert an approaching and concerning climate event: the loss of Arctic summer sea ice. We show that early deployment of feasible methane mitigation measures is essential to delaying and potentially even avoiding the loss of Arctic summer sea ice. Whether or not the sea ice is preserved beyond this century will ultimately depend on the level of concomitant carbon dioxide mitigation, but it is clear that sea ice will be at risk in the absence of methane mitigation. This analysis provides further justification of the value of early methane mitigation and supports the need to consider climate benefits beyond temperature when evaluating mitigation pathways.
Decide now or wait for the next forecast? Testing a decision framework using real forecasts and observations
Authors: Messori Gabriele , Jewson Stephen , Scher Sebastian
Published: March 2021

Users of meteorological forecasts are often faced with the question of whether to make a decision now based on the current forecast or whether to wait for a later and hopefully more accurate forecast before making the decision. Imagine that you are the organiser of an event planned for Saturday. If the weather conditions at the start of the event are unsuitable then the event will have to be cancelled, leading to various expenses. Daily weather forecasts are available in the run-up to the event and you need to use them to decide whether to cancel in advance or not. Cancelling early could lead to only small cancellation charges, while cancelling shortly before leads to larger charges. Both sets of cancellation charges are lower than the potential loss due to last-minute cancellation on Saturday, and this leads to a nuanced set of decisions around when and whether to cancel. The general mathematical framework for understanding decisions of this type has been studied extensively, both in meteorology and in other fields such as economics. In order to understand our problem of whether to decide now or wait for the next forecast, we consider a special case of this general framework, that is also an extension of the well-known cost-loss model. We find that within this extended cost-loss model, the question of whether to decide now or wait depends on probabilities of probabilities. We develop a decision algorithm which we apply to real forecasts of temperature, and find that the algorithm leads to better decisions in most settings relative to three simpler alternative decision-making schemes. Our results have implications for the additional kinds of information that weather and climate forecasters could produce to facilitate good decision making based on their forecasts.
The ephemeral development of C' shear bands
Authors: Finch Melanie , Bons Paul , Steinbach Florian , Griera Albert , Llorens Maria-Gema , Gomez-Rivas Enrique , Ran Hao , de Riese Tamara
Published: March 2021

C' shear bands are common structures in ductile shear zones but their development is poorly understood. They occur in rocks with a high mechanical strength contrast so we used numerical models of viscoplastic deformation to study the effect of the proportion of weak phase and the phase strength contrast on C' shear band development. We employed simple shear to a finite strain of 18 in 900 steps and recorded the microstructure, stress and strain distribution at each step. We found that C' shear bands form in models with ≥5% weak phase when there is a moderate or high phase strength contrast, and they occur in all models with weak phase proportions ≥15%. Contrary to previous research, we find that C' shear bands form when layers of weak phase parallel to the shear zone boundary rotate forwards. This occurs due to mechanical instabilities that are a result of heterogeneous distributions of stress and strain rate. C' shear bands form on planes of low strain rate and stress, not in sites of maximum strain rate as has previously been suggested. C' shear bands are ephemeral and they either rotate backwards to the C plane once they are inactive or rotate into the field of shortening and thicken to form X- and triangle- shaped structures.
The NOVAC database of volcanic SO2 emissions
Authors: Galle Bo ,   The NOVAC Collaboration
Published: March 2021

We present a detailed global data-set of volcanic sulphur dioxide (SO2) emissions during the period 2005-2017. Measurements were obtained by scanning-DOAS instruments of the NOVAC network at 32 volcanoes, and processed using a standardized procedure. We reveal the daily statistics of volcanic gas emissions under a variety of volcanological and meteorological conditions. Data from several volcanoes are presented for the first time. Our results  are compared with yearly averages derived from measurements from space by the Aura/OMI instrument and with historical inventories of GEIA. This comparison shows some interesting differences which reasons are briefly discussed. Data is openly available through the web repository at https://novac.chalmers.se/.
Slow earthquake signatures in the ratio between acoustic and internal gravity wave amplitudes in coseismic ionospheric disturbances
Authors: Heki Kosuke , Takasaka Yuki
Published: March 2021

Frequency spectra of seismic waves from a fault rupture reflects the size of the faults, i.e. relatively large amplitudes of long period waves are excited by larger earthquakes. Anomalies in rise times of the fault movements would also influence the spectra. For example, earthquakes characterized by slow faulting, known as tsunami earthquakes, excite large tsunamis for the amplitudes of short-period seismic waves. In this study, we compare amplitudes of long- and short-period atmospheric waves excited by vertical crustal movements associated with earthquake faulting. Such atmospheric waves often reach the ionospheric F region and cause coseismic ionospheric disturbances (CID) observed as oscillations in ionospheric total electron content (TEC), with ground Global Navigation Satellite System (GNSS) receivers. CID often includes long-period internal gravity wave (IGW) components in addition to short period acoustic wave (AW) components. The latter has a period of ~4 minutes and propagate by 0.8-1.0 km/s, while the former has a period of ~12 minutes and propagate as fast as 0.2-0.3 km/s. Here we compare amplitudes of these two different waves for five earthquakes, 2011 Tohoku-oki (Mw9.0), 2010 Maule (Mw8.8), 1994 Hokkaido-Toho-Oki (Mw8.3), 2003 Tokachi-oki (Mw8.0), and the 2010 Mentawai (Mw7.9) earthquakes, using data from regional dense GNSS networks. We found two important features, i.e. (1) larger earthquakes show larger IGW/AW amplitude ratios, and (2) Mentawai earthquake, a typical tsunami earthquake, exhibits abnormally large IGW amplitudes relative to AW amplitudes. These findings demonstrate that earthquakes with longer durations for faulting, or with longer times for vertical crustal movements, excite longer period atmospheric waves such as IGW more efficiently.
Earth System Models are not capturing observed tropical forest carbon dynamics
Authors: Koch Alexander , Hubau Wannes , Lewis Simon L.
Published: March 2021

The land surface is absorbing carbon from the atmosphere. Tropical forests play a key role in this carbon uptake. Recent analyses of 565 long-term forest inventory plots across Africa and Amazonia show that structurally intact tropical forest are a large carbon sink, but that this sink has recently saturated and is projected to be in long-term decline. Here we compare these results with estimates from the two most recent generations of Earth System Models, CMIP5 (19 models) and CMIP6 (17 models). We show that, while CMIP5 and CMIP6 are of similar skill, they do not reproduce the observed 1985-2014 carbon dynamics. The pan-tropical net sink from inventory data is 0.99 Pg C yr-1 (95% CI 0.7–1.3) between 2000–2010, the best sampled decade, double the CMIP6 multimodel-mean of 0.45 Pg C yr-1 (95% CI 0.35–0.55) over the same decade. The observed saturating and declining sink beginning in Amazonia in the 1990s and Africa in the 2010s is not captured by the models, which show modest increases in sink strength. The future pan-tropical net sink from the statistical model decreases by 0.23 Pg C per decade (95% CI 0.09–0.39) until the 2030s, while CMIP6 multimodel-means project an increasing carbon sink under all scenarios (0.01–0.03 Pg C per decade; 95% CI 0.00–0.06) except the low-CO2 scenario (-0.02 Pg C per decade; 95% CI -0.01–0.03). CMIP models balance positive CO2 fertilisation with negative responses to higher temperatures and droughts on carbon gains from tree growth similarly to observations, but the modelling of carbon losses from tree mortality does not correspond well to the inventory data. Reason for the model-observation differences is the treatment of mortality in models. Integrated research programs combining continued tropical forest monitoring and targeted experiments are needed to reduce the uncertainties in this key carbon cycle feedback in next-generation models.
Groundwater age from multi-level bores: What it can tell about the aquifers
Authors: Morgenstern Uwe , Rawlinson Zara
Published: March 2021

Geologic data to provide information on the functioning of aquifers is often scars. For the aquifers underlying the Heretaunga Plains, Hawkes Bay, one of New Zealand’s most important groundwater systems, we used groundwater age (tritium, SF6, 14C) to inform the geologic model and to provide information on groundwater flow through alternating strata of permeable river gravel beds and fine impermeable beds that form an interconnected unconfined–confined aquifer system with complex groundwater flow processes.

The aquifers are a result of geological processes responding to climate change cycles from cold glacial when sea level was more than 100m below present sea level, to warm interglacial periods with sea level similar to present day. Glacial climate strata are river gravel, sand and silt deposits and include the artesian aquifers. The interglacial strata form the aquicludes and are marine sand, silt, and clay deposits with interbedded estuarine, swamp and coastal fluvial silt, clay, peat and gravel deposits.

We have re-visited tracer data sampled during the drilling of multi-level observation well in the early 1990s, and collected new samples from these multi-level bores in order to understand in 3D the groundwater recharge sources, groundwater recharge and flow rates, connection to the rivers, and potential groundwater discharge out to sea. Consistently young water (c. 25 years) at depth greater than 100m indicates preferential flow paths, likely related to paleo-river channels. The flow pattern obtained from the water tracer data improves the geologic information from the drill-holes, and fits with information from recent airborne transient electromagnetic (SkyTEM) geophysical surveys.
Errors Introduced in Estimation of Surface Wave Phase and Group Velocities Due to Wrong Assumptions: An Assessment Using a Simple Model For Love Wave
Authors: Kharita Akash , Mukhopadhyay Sagarika
Published: March 2021

The surface wave phase and group velocities are estimated by dividing the epicentral distance by phase and group travel times respectively in all the available methods, this is based on the assumptions that (1) surface waves originate at the epicentre and (2) the travel time of the particular group or phase of the surface wave is equal to its arrival time to the station minus the origin time of the causative earthquake; However, both assumptions are wrong since surface waves generate at some horizontal distance away from the epicentre. We calculated the actual horizontal distance from the focus at which they generate and assessed the errors caused in the estimation of group and phase velocities by the aforementioned assumptions in a simple isotropic single layered homogeneous half space crustal model using the example of the fundamental mode Love wave. We took the receiver locations in the epicentral distance range of 100-1000 km, as used in the regional surface wave analysis, varied the source depth from 0 to 35 Km with a step size of 5 km and did the forward modelling to calculate the arrival time of Love wave phases at each receiver location. The phase and group velocities are then estimated using the above assumptions and are compared with the actual values of the velocities given by Love wave dispersion equation. We observed that the velocities are underestimated and the errors are found to be; decreasing linearly with focal depth, decreasing inversely with the epicentral distance and increasing parabolically with the time period. We also derived empirical formulas using MATLAB curve fitting toolbox that will give percentage errors for any realistic combination of epicentral distance, time period and depths of earthquake and thickness of layer in this model. The errors are found to be more than 5% for all epicentral distances lesser than 500 km, for all focal depths and time periods indicating that it is not safe to do regional surface wave analysis for epicentral distances lesser than 500 km without incurring significant errors. To the best of our knowledge, the study is first of its kind in assessing such errors.
The impact of policy measures on the spatial and temporal expansion of wind energy: a classification of instruments and modeling recommendations
Authors: Eicke Anselm , Mieth Stefanie , Pape Carsten , Reder Klara , Tiedemann Silvana
Published: March 2021

Policy measures influence the spatial and temporal deployment of wind energy often more than the geo-economical potential. On the national level, the design of renewable energy support schemes mostly determines the most promising locations for investments. These national instruments also interplay with regulation on the local and municipal level, including land development plans, licensing regimes, and local renewable energy targets. While modeling sometimes focuses on the national level, local regulations are most often absent from the analysis. Controversially, measures at the different administrative levels simultaneously foster and hinder the deployment of wind energy in some regions.

The contribution of this paper is threefold. First, we categorize policy measures at different administrative levels that influence the spatial expansion of wind energy. We uncover at which stage of the planning process these instruments play a role and by which mechanism they influence the spatial distribution and the development time. Second, we present and evaluate techniques to reflect such policy measures in spatial and temporal scenario models and discuss how to generalize them across countries and/or jurisdictions. Third, we apply these modelling techniques on the German case to gain insights on the pros and cons of different modelling approaches. The case study incorporates first scenarios from the Kopernikus project Ariadne.
The Paleochrono probabilistic model to derive a consistent chronology for several paleoclimatic sites
Authors: Parrenin Frédéric , Bazin Lucie , Buizert Christo , Capron Emilie , Chowdry Beeman Jai , Corrick Ellen , Drysdale Russell , Kawamura Kenji , Landais Amaëlle , Mulvaney Robert , Oyabu Ikumi , Rasmussen Sune
Published: March 2021

Past climatic and environmental changes can be reconstructed thanks to paleoclimatic archives such as ice cores, marine sediment cores, lake sediment cores, speleothems, tree rings, corals, etc. The dating of these natural archives is crucial for deciphering the temporal sequence of events during past climate changes. It is also essential to estimate the absolute and relative errors of such estimated chronologies. This task is, however, complex since it involves the combination of different dating approaches on different paleoclimatic sites and often different types of archives. Here we present Paleochrono, a new probabilistic model to derive a common and probalistically optimal chronology for several paleoclimatic sites with potentially different types of archives. Paleochrono is based on the inversion of an archiving model: a varying deposition rate (also named sedimentation or accumulation rate) and also, for ice cores, a lock-in-depth of air bubbles (since air is not trapped at surface) and a thinning function (since ice undergoes flow). The model integrates several types of chronological information: prior knowledge of the archiving process, independently dated horizons, depth intervals of known duration, undated stratigraphic links between records, and, for ice cores, Δdepth observations (depth differences between synchronous events recorded in the bubbles and ice, respectively). The optimization is formulated as a least-squares problem, assuming that all densities of probabilities are near-Gaussian and that the model is almost linear in the vicinity of the best solution. Paleochrono is the successor of IceChrono, which was dealing only with ice-core records. Paleochrono performs better than IceChrono in terms of computational efficiency, ease of use, and accuracy. We demonstrate the ability of Paleochrono in a new AICC2012-Hulu dating experiment, which combines the AICC2012 dating experiment, based on records from five polar ice cores, with data from two U/Th-dated speleothems from Hulu Cave (China). We analyse the performance of Paleochrono in terms of computing time and memory usage in various dating experiments. Paleochrono is freely available under the MIT open source license.
A novel method to identify subseasonal clustering episodes of extreme precipitation events and their contribution to large accumulations
Authors: Kopp Jérôme , Rivoire Pauline , Ali S. Mubashshir , Barton Yannick , Martius Olivia
Published: March 2021

Temporal clustering of extreme precipitation events on subseasonal time scales is a type of compound event, which can cause large precipitation accumulations and lead to floods. We present a novel count-based procedure to identify subseasonal clustering of extreme precipitation events. Furthermore, we introduce two metrics to characterise the frequency of subseasonal clustering episodes and their relevance for large precipitation accumulations. The advantage of this approach is that it does not require the investigated variable (here precipitation) to satisfy any specific statistical properties. Applying this methodology to the ERA5 reanalysis data set, we identify regions where subseasonal clustering of annual high precipitation percentiles occurs frequently and contributes substantially to large precipitation accumulations. Those regions are the east and northeast of the Asian continent (north of Yellow Sea, in the Chinese provinces of Hebei, Jilin and Liaoning; North and South Korea; Siberia and east of Mongolia), central Canada and south of California, Afghanistan, Pakistan, the southeast of the Iberian Peninsula, and the north of Argentina and south of Bolivia. Our method is robust with respect to the parameters used to define the extreme events (the percentile threshold and the run length) and the length of the subseasonal time window (here 2 – 4 weeks). The procedure could also be used to identify temporal clustering of other variables (e.g. heat waves) and can be applied on different time scales (e.g. for drought years). For a complementary study on the subseasonal clustering of European extreme precipitation events and its relationship to large-scale atmospheric drivers, please refer to Barton et al.
Petrological and zircon chemical record of arc magma evolution from long-lived batholith construction to giant porphyry copper deposit formation 
Authors: Nathwani Chetan , Simmons Adam , Large Simon , Wilkinson Jamie , Buret Yannick , Ihlenfeld Christian
Published: March 2021

Porphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene-Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~67 and ~59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu-Mo deposits that formed at 57-54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U-Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (>0.3) and lower Ti (<9 ppm) compositions after ~60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu-Mo deposits at Quellaveco, Toquepala and Cuajone from ~57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.
Visualizing the Seismic Wavefield with AlpArray
Authors: Ling On Ki Angel , Stähler Simon , Giardini Domenico , Group the AlpArray Working
Published: March 2021

The AlpArray Seismic Network (AASN) is a large-scale multidisciplinary seismic network in Europe that consists of over 600 3-component (3C) broadband stations with mean inter-station distance of 30-40km. This dense array allows the recording of the seismic wave propagation of distant earthquakes at a resolution of typical body and surface waves.

By animating the spatially-dense seismic recordings of the AASN, we can visualize seismic waves propagating across the European Alps as a function of space and time. Our 3C ground motion animations illustrate the full spatial-temporal evolution of global body and surface waves and demonstrates how a dense array allows the transformation from translation measurements at single stations to spatial gradients of the wavefield at the surface, capturing both small- and large-scale wave propagation phenomena. The addition of travel-time estimation, ray path illustration, and array-specific information such as slowness vector of incoming waves facilitate identification of seismic phases and their arrival-angle deviations. We will highlight some interesting observations of different seismic wave types in the animations of a few example teleseismic events during the course of the AASN between 2016-2019. Application for future research and education will also be discussed.