•Multiple satellite missions are used to monitor water storage components in the NCP.•Sentinel-3 altimetry and spectral/SAR imagery are used to monitor surface water storage.•South-to-North Water ...Diversion project has a significant impact on regional water storage dynamics.
Natural conditions of surface water bodies and groundwater aquifers in the North China Plain (NCP) have been altered to meet the ever-growing human water demands. Several water resources management measures have been implemented in recent decades to alleviate groundwater depletion, maintain ecological resilience, and sustain agricultural production. This study aims to investigate their impacts on land water storage, and thus obtain a picture of the spatio-temporal variation of water resources over the NCP. Based on multi-mission earth observation datasets, i.e., altimetry (Sentinel-3), synthetic aperture radar (SAR) and spectral imagery (Sentinel-1/2), gravimetry (GRACE/-FO), and microwave sensors (IMERG), as well as reanalysis datasets, we investigate surface water storage (SWS), soil moisture water storage (SMS), and total water storage (TWS) changes. Groundwater storage (GWS) change is subsequently estimated as the residual of the total storage equation.
Results show that TWS declined significantly over the past decades (−1.04 ± 0.05 cm/yr in 2004 to 2020), while SMS rebounded after a decreasing trend from 2004 to 2014. The spatial pattern of TWS variations depicts a particularly severe depletion along provincial boundaries. The SWS dynamics reveal that the volumes of three major NCP reservoirs (Guanting, Miyun, and Danjiangkou) increased significantly since around 2014 when the operation of the South-to-North Water Diversion Middle Route project (SNWDP-MR) started. Moreover, GWS maintained a depletion rate of −1.05 ± 0.08 cm/yr during 2004–2014 over the whole NCP, while the depletion rate accelerated during 2015–2020 (−1.88 ± 0.38 cm/yr). We also found that the GWS depletion in Beijing (−1.20 ± 0.10 cm/yr during 2004–2014 and −0.79 ± 0.44 cm/yr during 2015–2020) and its surrounding areas has been lowered possibly because of the SNWDP-MR. This study shows how multi-mission satellite earth observation products can be combined to monitor water resources at a regional scale and provide spatio-temporally resolved estimates of the impacts of human-induced changes in the inland water cycle.
•We present a parameter transfer framework for poorly gauged river catchments.•We apply the approach in three African river catchments.•We evaluate spatial patterns of hydrological processes to ...assess model coherence.•Parameter transfer based on similarity outperforms transfer based on proximity.
Development of robust hydrologic-hydrodynamic simulation models is challenging, especially in regions, where in-situ observation data are scarce. Parameter calibration is often a necessary and data-demanding step. Moreover, good calibration performance does not guarantee predictive skill in neighboring geographic regions or new time periods and scenarios. A robust calibration strategy is necessary and must apply an informed parameter regionalization approach, which can transfer parameter values from gauged to ungauged subcatchments, whilst accounting for data availability and quality. In this study, a calibration strategy combining a parameter transfer framework based on catchment similarities with a holistic calibration against hydrological signatures is presented to obtain reliable simulations at all relevant locations within a catchment. The approach is demonstrated for three African river catchments: the Tana, the Upper Niger and the Semliki catchments.
A rainfall-runoff model based on Budyko’s concept of limits with up to 11 calibration parameters and a daily simulation time step is used, coupled with a Muskingum routing scheme. Each river catchment is subdivided into so-called hydrological response units (HRU) based on climatic and physiographic characteristics. Multi-mission satellite remote sensing observations are used for the HRU classification: terrain slope derived from the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) and the publicly available European Space Agency (ESA) Climate Change Initiative (CCI) land cover map. Subcatchments within each HRU share the same parameters. The number of units is constrained by the number of in-situ stations available. The calibration strategy is a catchment-scale, multi-objective approach.
The method improved the overall model performance compared to a simpler, nearest-neighbor regionalization method. In particular, spatial patterns of the hydrological response are more reasonable and performance is improved at validation stations, highlighting the importance of appropriate parameter regionalization within nested catchments. With this method, a wider range of currently available remote sensing data (elevation, precipitation, land cover, etc.) can be exploited in hydrological model development and calibration.
Reservoir release is an essential variable as it affects hydrological processes and water availability downstream. This study aims to estimate reservoir release using a satellite-based approach, ...specially focusing on the impacts of inflow simulations and reservoir water storage change (RWSC) on release estimates. Ten inflow simulations based on hydrological models and blending schemes are used in combination with three RWSC estimates based on two satellite-based approaches. A case study is performed at the Ankang reservoir, China. The results demonstrate that release estimates show high skill, with normalized root-mean-square error (NRMSE) less than 0.12 and Kling-Gupta Efficiency (KGE) over 0.65. The performance of release estimates is varying with and influenced by inflow simulations and RWSC estimates, with NRMSE ranging from 0.09–0.12 and KGE from 0.65–0.74. Based on time-varying Bayesian Model Averaging (BMA) approaches and synthetic aperture radar (SAR) satellite datasets, more accurate inflow and RWSC estimates can be obtained, thus facilitating substantially release estimates. With multi-source satellite datasets, temporal scale of reservoir estimates is increased (monthly and bi-weekly), acting as a key supplement to in situ records. Overall, this study explores the possibility to reconstruct and facilitate reservoir release estimates in poorly gauged dammed basins using hydrological modeling techniques and multi-source satellite datasets.
Groundwater drought denotes the condition and hazard during a prolonged meteorological drought when groundwater resources decline and become unavailable or inaccessible for human use. Groundwater ...drought risk refers to the combined physical risk and human vulnerability associated with diminished groundwater availability and access during drought. An integrated management support tool, GRiMMS, is presented, for the mapping and assessment of relative groundwater drought risk in the Southern African Development Community (SADC) region. Based on composite mapping analysis of region-wide gridded relative indices of meteorological drought risk, hydrogeological drought proneness and human groundwater drought vulnerability, the mapping results highlight consistent areas across the region with highest groundwater drought risk and populations in the order of 39 million at risk of groundwater drought at present. Projective climate-model results suggest a potentially significant negative impact of climate change on groundwater drought risk. The tool provides a means for further attention to the key, but neglected, role of groundwater in drought management in Africa.
The paper presents results on the use of NOAA AVHRR data for desertification monitoring on a regional–global level. It is based on processing of the GIMMS 8 km global NDVI data set. Time series of ...annually integrated and standardized annual NDVI anomalies were generated and compared with a corresponding rainfall data set (1981–2003).
The regions studied include the Mediterranean basin, the Sahel from the Atlantic to the Red Sea, major parts of the drylands of Southern Africa, China–Mongolia and the drylands of South America, i.e. important parts of the desertification prone drylands of the world.
It is concluded that the suggested methodology is a robust and reliable way to assess and monitor vegetation trends and related desertification on a regional–global scale. A strong general relationship between NDVI and rainfall over time is demonstrated for considerable parts of the drylands. The results of performed trend analysis cannot be used to verify any systematic generic land degradation/desertification trend at the regional–global level. On the contrary, a “greening-up” seems to be evident over large regions.
The flow regime change of rivers, especially transboundary rivers, affected by reservoir regulations is evident worldwide and has received much attention. Investigating dam-induced flow regime ...alterations is essential for understanding potential adverse downstream effects and facilitating dialogue around coordinated water use in transboundary basins, such as the Lancang River Basin (LRB). This study explored the value of combining several types of satellite Earth observation (EO) datasets that monitor different water balance components to constrain the parameter space of lumped conceptual hydrological models. Thus, we aimed to reconstruct the natural flow regimes upstream and downstream of the cascade reservoirs. Specifically, reservoir water storage changes were first estimated using satellite imagery and altimetry datasets. Then, storage changes were combined with hydrological model simulations of reservoir inflow to estimate the regulated flow regime downstream. Our results showed that integrated hydrological modeling combined with EO datasets exhibited better overall performance. Continuous warming and drying of the LRB resulted in a decrease in discharge of approximately 47 %. By comparing the simulated natural and regulated flow regimes, we revealed the pivotal role of the Xiaowan and Nuozhadu reservoirs in regulating natural flows. The wet season shortens (approximately 45 days), the flood peak flattens, and the low flow in the dry season has primarily increases. The two reservoirs attenuated 50 % of the flood peaks in the wet seasons and mitigated droughts by releasing up to 100 % of the natural flows in the dry seasons at the China–Laos border. Overall, these results enhance the understanding of upper reservoir operation, and the approaches can be applied to studies of dammed basins under climate change scenarios when knowledge of the upstream area is limited.
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•We reconstructed the natural flow regime of the Lancang River by combining satellite Earth observations.•We obtained the regulated flow regime from satellite altimetry reservoir level observations.•We revealed the flow regime changes of the Lancang River during different periods.
Earth Observation (EO) data is a critical information source for mapping and monitoring water resources over large inaccessible regions where hydrological in-situ networks are sparse. In this paper, ...we present a simple yet robust method for fusing optical and Synthetic Aperture Radar (SAR) data for mapping surface water dynamics over mainland China. This method uses a multivariate logistic regression model to estimate monthly surface water extent over a four-year period (2017 to 2020) from the combined usages of Sentinel-1, Sentinel-2 and Landsat-8 imagery. Multi-seasonal high-resolution images from the Chinese Gaofen satellites are used as a reference for an independent validation showing a high degree of agreement (overall accuracy 94%) across a diversity of climatic and physiographic regions demonstrating potential scalability beyond China. Through inter-comparison with similar global scale products, this paper further shows how this new mapping technique provides improved spatio-temporal characterization of inland water bodies, and for better capturing smaller water bodies (< 0.81 ha in size). The relevance of the results is discussed, and we find this new enhanced monitoring approach has the potential to advance the use of Earth observation for water resource management, planning and reporting.
Methods by remote sensing techniques were developed to locate potential jökulhlaup lakes and to assess the volume of water discharged. To locate potential jökulhlaup lakes, a time sequence of LandSat ...satellite imagery covering the area was investigated with spectral mapping techniques. The investigations showed how LandSat images can be used to map surface water, glacial ice, and surface temporal anomalies, and when combined with geographic information system (GIS) analysis, potential jökulhlaup lakes could be identified. For assessing the volume of the water discharged, the bottom topography for the jökulhlaup lakes were mapped from stereo images acquired by the ASTER satellite sensor and thereby defining the relations between the lake surface areas and the volumes of water stored in the lakes. Annual lake areas outlined from LandSat images were combined with the area-volume relations to describe the change over time in the volume of water in the lakes and thereby the volume released during jökulhlaups. The results of the volume assessments were validated against recordings from a hydrological station in the downstream lake. The validation underpinned the credibility of the method and as it relies on satellite data that are readily available, the method is applicable for use in many areas of the world.
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