Groundwater Depletion in the Middle East from GRACE with Implications for Transboundary Water Management in the Tigris-Euphrates-Western Iran Region

In this study, we use observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission to evaluate freshwater storage trends in the north-central Middle East, including portions of the Tigris and Euphrates River Basins and western Iran, from January 2003 to December 2009. GRACE data show an alarming rate of decrease in total water storage of approximately -27.2 plus or minus 0.6 millimeters per year equivalent water height, equal to a volume of 143.6 cubic kimometers during the course of the study period. Additional remote-sensing information and output from land surface models were used to identify that groundwater losses are the major source of this trend. The approach used in this study provides an example of ''best current capabilities'' in regions like the Middle East, where data access can be severely limited. Results indicate that the region lost 17.3 plus or minus 2.1 millimeters per year equivalent water height of groundwater during the study period, or 91.3 plus or minus 10.9 cubic kilometers in volume. Furthermore, results raise important issues regarding water use in transboundary river basins and aquifers, including the necessity of international water use treaties and resolving discrepancies in international water law, while amplifying the need for increased monitoring for core components of the water budget

Mesures gravimétriques au sol et satellitaires: étude du rapport entre variation de pesanteur et déplacement vertical et apport de la mission spatiale GRACE à l'étude des surcharges hydrologiques et des très grands séismes

We model the ratio between gravity variation and ground vertical displacement that are due to a load located at the surface of a stratified, spherically symmetric and elastic earth model. Theoretical results are compared to numerical values found for different loads by using outputs of global models. We assess the resolution and the accuracy of the temporal variations of the water content in the ground estimated by the GRACE space gravity mission. These are compared to the seasonal variations predicted by several hydrological models. In Europe, the validation of the GRACE measurements by those of the GGP network gravimeters is based on a principal component analysis and highlights the drought of summer 2003. The gravitational coseismic and postseismic signatures of the Sumatra earthquake (2004) are extracted from the GRACE data. A modelling of the coseismic effect shows that the static response of the ocean must not be neglected.Nous modélisons le rapport entre variation de pesanteur et déplacement vertical du sol dus à une surcharge à la surface d'un modèle de Terre à symétrie sphérique, stratifié et élastique. Les résultats théoriques sont comparés aux valeurs numériques trouvées pour diverses charges à partir des sorties de modèles globaux. Nous évaluons la résolution et la précision des variations temporelles du contenu en eau du sol estimées par la mission de gravimétrie spatiale GRACE. Celles-ci sont comparées aux prédictions des variations saisonnières de plusieurs modèles hydrologiques. En Europe, la validation des mesures GRACE par les mesures des gravimètres du reseau GGP repose sur une analyse en composantes principales et met en évidence la sécheresse de l'été 2003. Les signatures gravitationnelles cosismique et postsismique associées au séisme de Sumatra (2004) sont extraites des données GRACE. Une modélisation de l'effet cosismique montre que la réponse statique de l'océan ne peut être negligée

Ground and space gravity measurements : study of the ratio between gravity variation and vertical displacement and contribution of the GRACE space mission to the study of hydrological loadings and very large earthquakes

Nous modélisons le rapport entre variation de pesanteur et déplacement vertical du sol dus à une surcharge à la surface d'un modèle de Terre à symétrie sphérique, stratifié et élastique. Les résultats théoriques sont comparés aux valeurs numériques trouvées pour diverses charges à partir des sorties de modèles globaux. Nous évaluons la résolution et la précision des variations temporelles du contenu en eau du sol estimées par la mission de gravimétrie spatiale GRACE. Celles-ci sont comparées aux prédictions des variations saisonnières de plusieurs modèles hydrologiques. En Europe, la validation des mesures GRACE par les mesures des gravimètres du réseau GGP repose sur une analyse en composantes principales et met en évidence la sécheresse de l'été 2003. Les signatures gravitationnelles cosismique et postsismique associées au séisme de Sumatra (2004) sont extraites des données GRACE. Une modélisation de l'effet cosismique montre que la réponse statique de l'océan ne peut être négligée.We model the ratio between gravity variation and ground vertical displacement that are due to a load located at the surface of a stratified, spherically symmetric and elastic earth model. Theoretical results are compared to numerical values found for different loads by using outputs of global models. We assess the resolution and the accuracy of the temporal variations of the water content in the ground estimated by the GRACE space gravity mission. These are compared to the seasonal variations predicted by several hydrological models. In Europe, the validation of the GRACE measurements by those of the GGP network gravimeters is based on a principal component analysis and highlights the drought of summer 2003. The gravitational coseismic and postseismic signatures of the Sumatra earthquake (2004) are extracted from the GRACE data. A modelling of the coseismic effect shows that the static response of the ocean must not be neglected

Ground and space gravity measurements : study of the ratio between gravity variation and vertical displacement and contribution of the GRACE space mission to the study of hydrological loadings and very large earthquakes

Nous modélisons le rapport entre variation de pesanteur et déplacement vertical du sol dus à une surcharge à la surface d'un modèle de Terre à symétrie sphérique, stratifié et élastique. Les résultats théoriques sont comparés aux valeurs numériques trouvéWe model the ratio between gravity variation and ground vertical displacement that are due to a load located at the surface of a stratified, spherically symmetric and elastic earth model. Theoretical results are compared to numerical values found for dif

Mesures gravimétriques au sol et satellitaires (étude du rapport entre variation de pesanteur et déplacement vertical et apport de la mission spatiale GRACE à l étude des surcharges hydrologiques et des très grands séismes)

Nous modélisons le rapport entre variation de pesanteur et déplacement vertical du sol dus à une surcharge à la surface d un modèle de Terre à symétrie sphérique, stratifié et élastique. Les résultats théoriques sont comparés aux valeurs numériques trouvées pour diverses charges à partir des sorties de modèles globaux. Nous évaluons la résolution et la précision des variations temporelles du contenu en eau du sol estimées par la mission de gravimétrie spatiale GRACE. Celles-ci sont comparées aux prédictions des variations saisonnières de plusieurs modèles hydrologiques. En Europe, la validation des mesures GRACE par les mesures des gravimètres du réseau GGP repose sur une analyse en composantes principales et met en évidence la sécheresse de l été 2003. Les signatures gravitationnelles cosismique et postsismique associées au séisme de Sumatra (2004) sont extraites des données GRACE. Une modélisation de l effet cosismique montre que la réponse statique de l océan ne peut être négligée.We model the ratio between gravity variation and ground vertical displacement that are due to a load located at the surface of a stratified, spherically symmetric and elastic earth model. Theoretical results are compared to numerical values found for different loads by using outputs of global models. We assess the resolution and the accuracy of the temporal variations of the water content in the ground estimated by the GRACE space gravity mission. These are compared to the seasonal variations predicted by several hydrological models. In Europe, the validation of the GRACE measurements by those of the GGP network gravimeters is based on a principal component analysis and highlights the drought of summer 2003. The gravitational coseismic and postseismic signatures of the Sumatra earthquake (2004) are extracted from the GRACE data. A modelling of the coseismic effect shows that the static response of the ocean must not be neglected.STRASBOURG-EOST (674822249) / SudocSudocFranceF

Retrieval of Large-Scale Hydrological Signals in Africa from GRACE Time-Variable Gravity Fields

International audienceSince its launch in April 2002, the Gravity Recovery and Climate Experiment (GRACE) mission is recording the Earth's time-variable gravity field with temporal and spatial resolutions of typically 7-30 days and a few hundreds of kilometers, allowing the monitoring of continental water storage variations from both continental and river-basin scales. We investigate here large scale hydrological variations in Africa using different GRACE spherical harmonic solutions, using different processing strategies (constrained and unconstrained solutions). We compare our GRACE estimates to different global hydrology models, with different landsurface schemes and also precipitation forcing. We validate GRACE observations through two different techniques: first by studying desert areas, providing an estimate of the precision. Then we compare GRACE recovered mass variations of main lakes to volume changes derived from radar altimetry measurements. We also study the differences between different publicly available precipitation datasets from both space measurements and ground rain gauges, and their impact on soil-moisture estimates

Estimating snow water equivalent from GPS vertical site-position observations in the western United States

 Accurate estimation of the characteristics of the winter snowpack is crucial for prediction of available water supply, flooding, and climate feedbacks. Remote sensing of snow has been most successful for quantifying the spatial extent of the snowpack, although satellite estimation of snow water equivalent (SWE), fractional snow covered area, and snow depth is improving. Here we show that GPS observations of vertical land surface loading reveal seasonal responses of the land surface to the total weight of snow, providing information about the stored SWE. We demonstrate that the seasonal signal in Scripps Orbit and Permanent Array Center (SOPAC) GPS vertical land surface position time series at six locations in the western United States is driven by elastic loading of the crust by the snowpack. GPS observations of land surface deformation are then used to predict the water load as a function of time at each location of interest and compared for validation to nearby Snowpack Telemetry observations of SWE. Estimates of soil moisture are included in the analysis and result in considerable improvement in the prediction of SWE

Gravity Recovery and Climate Experiment (GRACE) detection of water storage changes in the Three Gorges Reservoir of China and comparison with in situ measurements

Water impoundment in the Three Gorges Reservoir (TGR) of China caused a large mass redistribution from the oceans to a concentrated land area in a short time period. We show that this mass shift is captured by the Gravity Recovery and Climate Experiment (GRACE) unconstrained global solutions at a 400 km spatial resolution after removing correlated errors. The WaterGAP Global Hydrology Model (WGHM) is selected to isolate the TGR contribution from regional water storage changes. For the first time, this study compares the GRACE (minus WGHM) estimated TGR volume changes with in situ measurements from April 2002 to May 2010 at a monthly time scale. During the 8 year study period, GRACE-WGHM estimated TGR volume changes show an increasing trend consistent with the TGR in situ measurements and lead to similar estimates of impounded water volume. GRACE-WGHM estimated total volume increase agrees to within 14% (3.2 km(3)) of the in situ measurements. This indicates that GRACE can retrieve the true amplitudes of large surface water storage changes in a concentrated area that is much smaller than the spatial resolution of its global harmonic solutions. The GRACE-WGHM estimated TGR monthly volume changes explain 76% (r(2) = 0.76) of in situ measurement monthly variability and have an uncertainty of 4.62 km(3). Our results also indicate reservoir leakage and groundwater recharge due to TGR filling and contamination from neighboring lakes are nonnegligible in the GRACE total water storage changes. Moreover, GRACE observations could provide a relatively accurate estimate of global water volume withheld by newly constructed large reservoirs and their impacts on global sea level rise since 2002

Gravity Recovery and Climate Experiment (GRACE) detection of water storage changes in the Three Gorges Reservoir of China and comparison with in situ measurements

Water impoundment in the Three Gorges Reservoir (TGR) of China caused a large mass redistribution from the oceans to a concentrated land area in a short time period. We show that this mass shift is captured by the Gravity Recovery and Climate Experiment (GRACE) unconstrained global solutions at a 400 km spatial resolution after removing correlated errors. The WaterGAP Global Hydrology Model (WGHM) is selected to isolate the TGR contribution from regional water storage changes. For the first time, this study compares the GRACE (minus WGHM) estimated TGR volume changes with in situ measurements from April 2002 to May 2010 at a monthly time scale. During the 8 year study period, GRACE-WGHM estimated TGR volume changes show an increasing trend consistent with the TGR in situ measurements and lead to similar estimates of impounded water volume. GRACE-WGHM estimated total volume increase agrees to within 14% (3.2 km(3)) of the in situ measurements. This indicates that GRACE can retrieve the true amplitudes of large surface water storage changes in a concentrated area that is much smaller than the spatial resolution of its global harmonic solutions. The GRACE-WGHM estimated TGR monthly volume changes explain 76% (r(2) = 0.76) of in situ measurement monthly variability and have an uncertainty of 4.62 km(3). Our results also indicate reservoir leakage and groundwater recharge due to TGR filling and contamination from neighboring lakes are nonnegligible in the GRACE total water storage changes. Moreover, GRACE observations could provide a relatively accurate estimate of global water volume withheld by newly constructed large reservoirs and their impacts on global sea level rise since 2002