nasa-gesdisc/es-publications-researchareas huggingface dataset:
Identifying global hotspots where coastal wetland conservation can contribute to nature-based mitigation of coastal flood risks (2020)

Low-lying coastal zones are increasingly exposed to flood risks due to global change including sea level rise, increasing storm intensity and growing coastal population densities. Local to regional-scale studies have demonstrated that conservation or restoration of coastal wetland ecosystems, such as salt marshes and mangroves, provides nature-based risk mitigation, as these wetlands have the natural capacity to mitigate the impacts of storm surges and related flood risks. Yet, it is unknown how important this nature-based mitigation of coastal flood risks is on a global scale. Here we present the results of a global-scale GIS model assessing the global distribution of inland surface areas and population numbers exposed to storm surges that would first propagate through tidal wetlands before they reach the inhabited land, and hence that would receive storm surge mitigation by the mangrove forests and salt marshes. Further our model quantifies the distance travelled by a storm surge through the tidal wetlands as a measure of the magnitude of storm surge mitigation. Results show that on a worldwide scale, about 30% of the flood-exposed low-lying coastal plain benefits from nature-based storm surge mitigation by tidal wetlands, with the largest areas located in deltas (e.g. Pearl River, Yangtze, Mekong) and estuaries (e.g. Elbe). Areas protected by large wetlands, where a storm surge would first propagate through >5 km of tidal wetlands before it reaches vulnerable land and people, are located in river deltas such as of the Guayas (Ecuador), Mississippi (USA) and Ganges-Brahmaputra (India and Bangladesh). About 35% of the global flood-exposed coastal population receives nature-based storm surge mitigation. The majority of that population (80%) is located in five countries, i.e. China, Vietnam, the Netherlands, India and Germany. Areas more exposed to extreme storm surges (Eastern America, Caribbean Sea, Eastern Asia) include hotspot areas where storm surges are travelling through wider tidal wetlands generating higher risk mitigation, as for example in the Mississippi delta, Chesapeake bay, Ganges-Brahmaputra delta or Yangtze delta. Our global assessment aims to increase general awareness on the capacity of nature-based coastal flood risk mitigation, and to stimulate further local scale analyses in support of its wider application around the world.

Research areas: Floods
Application of Unmanned Aerial Vehicle DEM in flood modeling and comparison with global DEMs: Case study of Atrak River Basin, Iran (2022)

Digital Elevation Models (DEMs) play a significant role in hydraulic modeling and flood risk management. This study initially investigated the effect of Unmanned Aerial Vehicle (UAV) DEM resolutions, ranging from 1 m to 30 m, on flood characteristics, including the inundation area, mean flow depth, and mean flow velocity. Then, the errors of flood characteristics for global DEMs, comprising ALOS (30 m), ASTER (30 m), SRTM (30 m), and TDX (12 m) were quantified using UAV DEM measurements. For these purposes, the HEC-RAS 2D model in steady-state conditions was used to simulate the flood with return periods of 5- to 200 years along 20 km reach of Atrak River located in northeastern Iran. Results indicated when UAV DEM resolution decreased from 1 m to 30 m, inundation area and mean flow depth increased 17.0% (R2 = 0.94) and 10.2% (R2 = 0.96) respectively, while mean flow velocity decreased 16.8% (R2 = 0.94). Validation of the hydraulic modeling using the modified normalized difference water index demonstrated that the HEC-RAS 2D model in conjunction with UAV DEM simulates the flood with 92% accuracy. Comparing the global DEMs with UAV DEM showed that the root mean square error (RMSE) values of the flow depth for ASTER, SRTM, ALOS, and TDX DEMs were 1.77, 1.12, 1.02, and 0.93 m, and the RMSE values of the flow velocity for the same DEMs were 0.81, 0.66, 0.55, and 0.47 m/s, respectively. Furthermore, TDX DEM with a 6.15% error in the inundation area was the nearest to UAV measurements. Overall, TDX DEM revealed a better performance in hydraulic modeling of the fluvial flood characteristics. Hence, it is recommended for environments where high-resolution topography data is scarce. The results of this study could potentially serve as a guideline for selecting global DEMs for hydraulic simulations.

Research areas: Floods
Realizing the full reservoir operation potential during the 2020 Yangtze river floods (2022)

Five severe floods occurred in the Yangtze River Basin, China, between July and August 2020, and the Three Gorges Reservoir (TGR) located in the middle Yangtze River experienced the highest inflow since construction. The worlds largest cascade-reservoir group, which counts for 22 cascade reservoirs in the upper Yangtze River, cooperated in real time to control floods. The cooperation prevented evacuation of 600,000 people and extensive inundations of farmlands and aquacultural areas. In addition, no water spillage occurred during the flood control period, resulting in a world-record annual output of the TGR hydropower station. This work describes decision making challenges in the cooperation of super large reservoir groups based on a case-study, controlling the 4th and 5th floods (from Aug-14 to Aug-22), the efforts of technicians, multi-departments, and the state, and reflects on these. To realize the full potential of reservoir operation for the Yangtze River Basin and other basins with large reservoir groups globally, we suggest: (i) improve flood forecast accuracy with a long leading time; (ii) strengthen and further develop ongoing research on reservoir group cooperation; and (iii) improve and implement institutional mechanisms for coordinated operation of large reservoir groups.

Research areas: Floods
Brief communication: Comparing hydrological and hydrogeomorphic paradigms for global flood hazard mapping (2020)

Abstract. Global floodplain mapping has rapidly progressed over the past few years. Different methods have been proposed to identify areas prone to river flooding, resulting in a plethora of available products. Here we assess the potential and limitations of two main paradigms and provide guidance on the use of these global products in assessing flood risk in data-poor regions.

Research areas: Floods
Towards a global seasonal and permanent reference water product from Sentinel-1/2 data for improved flood mapping (2022)

Satellite-based flood mapping has become an important part of disaster response. In order to accurately distinguish flood inundation from normally present conditions, up-to-date, high-resolution information on the seasonal water cover is crucial. This information is usually neglected in disaster management, which may result in a non-reliable representation of the flood extent, mainly in regions with highly dynamic hydrological conditions. In this study, we present a fully automated method to generate a global reference water product specifically designed for the use in global flood mapping applications based on high resolution Earth Observation data. The proposed methodology combines existing processing pipelines for flood detection based on Sentinel-1/2 data and aggregates permanent as well as seasonal water masks over an adjustable reference time period. The water masks are primarily based on the analysis of Sentinel-2 data and are complemented by Sentinel-1-based information in optical data scarce regions. First results are demonstrated in five selected study areas (Australia, Germany, India, Mozambique, and Sudan), distributed across different climate zones and are systematically compared with external products. Further, the proposed product is exemplary applied to three real flood events in order to evaluate the impact of the used reference water mask on the derived flood extent. Results show, that it is possible to generate a consistent reference water product at 1020 m spatial resolution, that is more suitable for the use in rapid disaster response than previous masks. The proposed multi-sensor approach is capable of producing reasonable results, even if only few or no information from optical data is available. Further it becomes clear, that the consideration of seasonality of water bodies, especially in regions with highly dynamic hydrological and climatic conditions, reduces potential over-estimation of the inundation extent and gives a more reliable picture on flood-affected areas.

Research areas: Floods
Brief communication: Western Europe flood in 2021  mapping agriculture flood exposure from synthetic aperture radar (SAR) (2022)

Abstract. In this communication, we present the exposure of agricultural lands to the flooding caused by extreme precipitation in western Europe from 12 to 15 July 2021. Overlaying the flood inundation maps derived from the near-real-time RAdar-Produced Inundation Diary (RAPID) system on the Coordination of information on the environment (CORINE) Land Cover map we estimate a 1920 km2 area affected by the flooding, with 64 % representing agricultural land. Among the inundated agricultural land, 36 % of the area is pastures while 34 % is arable land. Most agricultural flood exposure is found in eastern France along the Rhone River, the southern Netherlands along the Meuse River, and western Germany along the Rhine River.

Research areas: Floods
Sustainable Management, Conservation, and Restoration of the Amazon River Delta and Amazon-Influenced Guianas Coast: A Review (2021)

The Amazon River delta may be currently characterized biophysically as a relatively preserved delta compared to the rampant vulnerability of many of the worlds large deltas. This status of relative preservation is reflected in a number of criteria: The still largely free-flowing nature of many of the rivers and the main stem of the Amazon that feed the delta in sediment, exceptional biodiversity, dominant shoreline accretion, and the absence of anthropogenically-generated subsidence. In this review, we show that these relatively reassuring conditions are progressively being called into question by the effects of dams on fluvial sediment supply to the delta, by increasing demographic, urban, and land development pressures in this still largely underpopulated delta, and by problems of governance that underplay aspects of basin-wide and deltaic environmental deterioration. A major challenge is that of bringing together these contrasting demands that are leading to the emergence of zones of environmental stress that test the resilience of this delta. An integral part of the strategy for the analysis of collective action, management, and conservation is that of considering the Amazon delta in terms of interacting socio-ecological systems. Pressures on the delta will be compounded in the future by decreasing fluvial sediment supply and sea-level rise. Although climate change is projected to generate surplus sediment, the rapid growth of dam constructions upstream of the delta will negatively impact the rivers sediment flux. Conservation and management of the Amazon River system aimed at keeping the delta resilient in the context of sea-level rise and reduction of sediment supply will require clear governance and better planning and anticipation, as well as socio-ecological integration. These are also requirements that will need to be implemented in the 1500 km-long coastal zone of the Guianas countries located west of the Amazon delta and the sediment dynamics and stability of which are largely determined by sediment supply from the Amazon.

Research areas: Land Surface/Agriculture Indicators
Sea Level‐Driven Marsh Migration Results in Rapid Net Loss of Carbon (2021)

Sea level rise alters coastal carbon cycling by driving the rapid migration of coastal ecosystems, salinization of freshwater systems, and replacement of terrestrial forests with tidal wetlands. Wetland soils accumulate carbon (C) at faster rates than terrestrial soils, implying that sea level rise may lead to enhanced carbon accumulation. Here, we show that carbon stored in tree biomass greatly exceeds carbon stored in adjacent marsh soils so that marsh migration reduces total carbon stocks by ∼50% in less than 100 years. Continued marsh soil carbon accumulation may eventually offset forest carbon loss, but we estimate that the time for replacement is similar to estimates of marsh survival (i.e., centuries), which suggests that forest C may never be replaced. These findings reveal a critical C source not included in coastal C budgets driven by migrating ecosystems and rapidly shifting allocations between carbon stored in soils and biomass.

Research areas: Ecosystems
Bonnet Carré Spillway freshwater transport and corresponding biochemical properties in the Mississippi Bight (2020)

Large freshwater pulses to coastal ecosystems change local hydrologic regimes and alter biogeochemical processes. The Mississippi Bight coastal ecosystem, located in the northern Gulf of Mexico shelf, is influenced by extensive freshwater inputs: the Mississippi River (MSR) and several smaller rivers to the east. Under river flood conditions, MSR waters flow through the Bonnet Carre Spillway (BCS) to relieve pressure on levees in New Orleans, Louisiana. In 2015, mild wintertime temperatures and heavy rainfall throughout the MSR watershed led to extreme flooding and prompted an unusually early BCS opening on January 10, 2016 for 23 days. This study examines the effects of such intermittent freshwater diversions on local shelf circulation, planktonic distributions, and potential contaminant transport pathways. Physical, chemical, and remote sensing data collected one month after the BCS opening suggested the region was comprised of three water masses: shelf saltwater, MSR waters, and local river waters. Observations and circulation model results showed the BCS waters remained within the estuarine lakes and sounds, where winter wind patterns mixed the waters and prevented BCS waters from flowing onto the shelf. Freshwater within the Mississippi Bight was primarily from concurrent flooding of local rivers. Two distinct clusters of microplankton (offshore versus nearshore stations) and zooplankton (Chandeleur Sound versus other stations) community compositions were detected. No algal blooms were observed during this BCS opening. The 2016 wintertime BCS opening resulted in muted effects on the sounds and shelf because of its short duration and uncharacteristically early release.

Research areas: Floods
Pre‐emergence herbicides, not carrier volume, impacted weed management in conventional tillage systems (2021)

The use of pre‑emergence (PRE) herbicides is resurging as a standard practice for weed management in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in the U.S. north‑central region. The increased use of PRE herbicides warrants investigation on the impact of spray carrier volume on weed control. Field experiments were established at Arlington, WI, in 2018 and 2019 and Janesville, WI, in 2018 to evaluate the influence of carrier volume on weed control of PRE herbicides in conventional tilled corn and soybean. Each experiment included three PRE herbicide premixes applied at crop planting at five carrier volumes (2.5, 5, 10, 15, and 17.5 gal acre−1). A nontreated control was also included in the experiment. Carrier volume did not influence weed control but PRE herbicide selection did. In corn, acetochlor + clopyralid + mesotrione and bicyclopyrone + mesotrione + S‑metolachlor provided 10–13% better annual grass, common ragweed (Ambrosia artemisiifolia L.), and giant ragweed (A. trifida L.) control than fluthiacet‑methyl + pyroxasulfone. In soybean, dimethenamid‑P + saflufenacil resulted in similar common ragweed control as the flumioxazin + pyroxasulfone treatment (79–85%), and 6 and 14% higher annual grass control and biomass reduction, respectively, compared to metribuzin + chlorimuron‑ethyl at Arlington. At Janesville, due to the high giant ragweed density in soybean, all herbicide treatments provided low levels of giant ragweed control (48–56%). Results from these field experiments suggest that lower carrier volumes could be used for PRE herbicide applications without compromising weed control in conventional tillage systems.Core Ideas Spray carrier volume did not influence weed control of corn and soybean pre‑emergence herbicides in conventional tillage systems. Pre‑emergence herbicide selection influenced weed control in corn and soybean under conventional tillage systems. Effective pre‑emergence herbicides can be utilized at lower spray carrier volumes without compromising their efficacy in conventional tillage systems.

Research areas: Agriculture
Bridging the gap between terrestrial, riverine and limnological research: Application of a model chain to a mesotrophic lake in North America (2018)

Models remain our best available tool for managing low lake dissolved oxygen concentrations, which pose a serious ecological risk. This study investigated whether process-based catchment models (INCA-N and INCA-P) could accurately drive a lake model (PROTECH), to bridge a gap between terrestrial, riverine and limnological research. INCA was calibrated over all 20 catchments of the Simcoe watershed, Canada. Daily outputs (flow, nitrogen and phosphorus concentrations) over the period 20102016 were selected for a common baseline period, and used as inputs to PROTECH, which was calibrated across the three major basins of lake Simcoe; Kempenfelt (K42), Cooks (C9), and the main basin (E51). Results showed that at catchment outflows INCA models achieved an average flow R2 of 0.8; a load R2 of 0.7 (both for TP and N-NO3), a concentration R2 of 0.4 and 0.5 (for TP and N-NO3 respectively), and an SiO2 R2>0.8. In each basin PROTECH achieved an R2 for both temperature and dissolved oxygen (DO) concentrations of >0.9. Performance of N-NO3, TP and Chlorophyll-a concentrations were good (R2 values of up to 0.98, 0.92 and 0.53 respectively). Multi-stressor analyses established that most occurrences when DO dropped below the desired 7mg/l threshold (DO7) were attributable to combinations of high temperatures and low tributary inflows. The importance of additional drivers was depth dependent, with photosynthesis being particularly important in shallower C9 and E51 basins during summer, when algae contributed sufficient O2 to the water column to inhibit DO7 events. Conversely in the deeper more strongly stratified K42 basin, greater algal growth boosted the biochemical oxygen demand, enhancing declines in DO. Lake physics explained a significant number of DO7 events in all three basins. Integrated catchment-lake modelling approaches are important in understanding lake physical and ecological processes, and the impacts of land management and future climate change.

Research areas: Water Quality
Causes & effects of upstream-downstream flow regime alteration over Catchment-Estuary-Coastal systems (2023)

The construction of large dams along rivers has significantly changed the natural flow regime, reducing the inflow into many lakes and terminal wetlands. However, the question of the impact of dam operation on downstream estuarine wetlands has less been taken into account. Spatio-temporal flow regime alteration in the Mond River shows the complexity of drivers affecting the estuary-coastal system named the Mond-Protected Area in southern Iran. To this end, we applied river impact (RI) and Indicator of hydrological alteration (IHA) methods on monthly and daily river flow data across the basin. Based on the river impact method, a drastic impact below two in-operation (Tangab and Salman Farsi) dams, with RI values of 0.02 and 0.08, diminish to a severe impact with RI value of 0.35 at the last gauge (Ghantareh) on the main corridor of the Mond river due to the addition of flow from a large mid-basin (about 20,254 km2). Furthermore, the degree of hydrological alteration (daily flow analysis) at mid-stream (e.g., Dehram gauges) was similar to the unregulated upstream tributaries (e.g., Hanifaghan gauges). The remote sensing analysis in the Mond Protected Area showed the prevailing impact of sea-level rise in the Persian Gulf with the inundation of the coastal area and a shift of vegetation in a landward direction which complied with standardized precipitation index (SPI) values as a meteorological drought indicator. Thus, the consequence of climate change (e.g., sea-level rise, draught) has a higher impact on the protected area than the upstream river regulation and land-use change in the Mond basin. The holistic approach and the catchment-level study allowed us to see the complexity of the drivers influencing the estuary-coastal system.

Research areas: Habitat Conversion/Fragmentation
Marked isotopic variability within and between the Amazon River and marine dissolved black carbon pools (2019)

Riverine dissolved organic carbon (DOC) contains charcoal byproducts, termed black carbon (BC). To determine the significance of BC as a sink of atmospheric CO2 and reconcile budgets, the sources and fate of this large, slow-cycling and elusive carbon pool must be constrained. The Amazon River is a significant part of global BC cycling because it exports an order of magnitude more DOC, and thus dissolved BC (DBC), than any other river. We report spatially resolved DBC quantity and radiocarbon (14C) measurements, paired with molecular-level characterization of dissolved organic matter from the Amazon River and tributaries during low discharge. The proportion of BC-like polycyclic aromatic structures decreases downstream, but marked spatial variability in abundance and 14C values of DBC molecular markers imply dynamic sources and cycling in a manner that is incongruent with bulk DOC. We estimate a flux from the Amazon River of 1.92.7 Tg DBC yr1 that is composed of predominately young DBC, suggesting that loss processes of modern DBC are important.

Research areas: Water Quality
Dynamics of evapotranspiration over a non-irrigated alfalfa field in the Southern Great Plains of the United States (2019)

Accurately quantifying the dynamics of evapotranspiration (ET) is crucial for efficient water management and improved water use efficiency. However, details on the magnitudes and annual dynamics of ET with respect to environmental/biophysical factors and harvesting of hay in non-irrigated alfalfa (Medicago sativa L.) are lacking. Using the eddy covariance (EC) technique, daily magnitudes and seasonal/annual dynamics and budgets of ET were quantified from April 2016 to May 2018 over a non-irrigated alfalfa field in central Oklahoma, USA. The field was harvested periodically for hay, and cumulative dry forage yield was approximately 7.5 and 10 t ha1 in 2016 (dry year) and 2017 (wet year), respectively. Daily ET reached up to 6.9 mm d1 and 8-day average ET reached up to 5.64 mm d1. Cumulative seasonal (April-October) ET was 652 mm (1.3 times of precipitation) in 2016 and 734 mm (0.8 times of precipitation) in 2017. Annual ET in 2017 was 900 mm (0.8 times of annual precipitation). Optimum air temperature (Ta) and vapor pressure deficit (VPD) for ET were approximately 30 C and 3 kPa, respectively. Higher forage production was associated with a greater increase (22%) in carbon uptake (gross primary production, GPP) than ET (13%) in 2017 compared to 2016. Consequently, ecosystem water use efficiency (EWUE) at the seasonal scale (seasonal sums of GPP to ET) was 2.38 and 2.57 g C mm1 ET in 2016 and 2017, respectively. Despite strong correspondence (R2 = 0.73) between EC-measured ET and Moderate Resolution Imaging Spectroradiometer (MODIS)-derived ET (ETMOD16), the standard ETMOD16 product underestimated ET by 36% compared to EC-measured ET. The MODIS-derived enhanced vegetation index (EVI) and photosynthetically active radiation (PAR) explained 83% of variations in alfalfa ET, indicating the potential of integrating remote sensing observations and climate data to extrapolate site-level alfalfa ET at larger areas.

Research areas: Land Surface/Agriculture Indicators