Satellite Observations of Regional Drought Severity in the Continental United States Using GRACE-Based Terrestrial Water Storage Changes

Drought monitoring is important for characterizing the timing, extent, and severity of drought for effective mitigation and water management. Presented here is a novel satellite-based drought severity index (DSI) for regional monitoring derived using time-variable terrestrial water storage changes from the Gravity Recovery and Climate Experiment (GRACE). The GRACE-DSI enables drought feature comparison across regions and periods, it is unaffected by uncertainties associated with soil water balance models and meteorological forcing data, and it incorporates water storage changes from human impacts including groundwater withdrawals thatmodify land surface processes and impact water management. Here, the underlying algorithm is described, and the GRACEDSI performance in the continental United States during 2002–14 is evaluated. It is found that the GRACE-DSI captures documented regional drought events and shows favorable spatial and temporal agreement with the monthly Palmer Drought Severity Index (PDSI) and the U.S. Drought Monitor (USDM). The GRACE-DSI also correlateswellwith a satellite-based normalized difference vegetation index (NDVI), indicating sensitivity to plantavailable water supply changes affecting vegetation growth. Because the GRACE-DSI captures changes in total terrestrial water storage, it complements more traditional drought monitoring tools such as the PDSI by providing information about deeper water storage changes that affect soil moisture recharge and drought recovery. The GRACE-DSI shows potential for globally consistent and effective drought monitoring, particularly where sparse ground observations (especially precipitation) limit the use of traditional drought monitoring methods

Utilization of Remote Sensing Data for Estimation of the Groundwater Storage Variation

Groundwater is the most extracted raw material, with an average withdrawal rate of 982 km3 per year, where 70 percent of the total groundwater withdrawn is used for agriculture globally (Margat & van der Gun, 2013). With climate change and increased water demands in recent years, monitoring the changes in the groundwater storage is of the utmost importance. This thesis presents an analysis that determines the rates, trends, and directions where groundwater storage is going in Pakistan. It also correlates fluctuations in groundwater storage with variations in precipitation and agricultural productivity in the country. The overall objectives of this thesis are to identify the long-term variations in groundwater storage, and examine the impact of precipitation and crop production on the groundwater reserves in Pakistan. In this thesis, The Gravity Recovery and Climate Experiment (GRACE) satellite data are used to estimate changes in groundwater storage for the study period of April 2002 – June 2017. By subtracting the different water subcomponents, i.e. soil moisture and snow water equivalent, derived from the Global Land Data Assimilation System (GLDAS) Noah from the GRACE data products, variations in groundwater storage are estimated. Precipitation data for this study is obtained from the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) CDR system. Agricultural information, which includes the crop water requirement, is derived from CROPWAT, and yield data are obtained from the Bureau of Statistics, Punjab. The results reveal that groundwater storage in Pakistan is declining at a high rate. Over a period of 183 months, Punjab province has observed the highest loss in total volume of groundwater storage (28.2 km3), followed by Balochistan (19.57 km3), Khyber Pakhtunkhwa (9.84 km3), and lastly, Sindh (5.46 km3). The results also show that precipitation has a weak positive impact on groundwater storage and soil moisture, depending on the region. Lastly, crop cultivation has had a significant impact on the groundwater withdrawal rates, with amounts varying on a district by district basis. The contributions of this study include a better understanding of variations in the groundwater storage across different provinces in Pakistan, and an analysis of the effect of groundwater changes in relation to crop water demand and precipitation. GRACE data can be used to assess groundwater depletion in areas where groundwater monitoring is not available, as it can help with the evaluation of decreasing trends in groundwater levels. It can also provide policy makers information needed to conserve groundwater resources for future use

Emerging Trends in Global Freshwater Availability

Freshwater availability is changing worldwide. Here we quantify 34 trends in terrestrial water storage (TWS) observed by the Gravity Recovery and Climate Experiment (GRACE) satellites during 2002-2016 and categorize their drivers as natural interannual variability, unsustainable groundwater consumption, or climate change. Several of these trends had been lacking thorough investigation and attribution, including massive changes in northwestern China and the Okavango delta. Others are consistent with climate model predictions. This observation-based assessment of how the world's water landscape is responding to human impacts and climate variations provides a blueprint for evaluating and predicting emerging threats to water and food security

Spatio temporal pattern in the changes in availability and sustainability of water resources in Afghanistan

Water is gradually becoming scarce in Afghanistan like in many other regions of the globe. The objective of this study was to evaluate the spatial changes in the availability and sustainability of water resources in Afghanistan. The Terrestrial Water Storage (TWS) data of the Gravity Recovery and Climate Experiment (GRACE) satellite obtained from three different institutes, having 1° × 1° spatial resolutions for the period 2002–2016 was used for this purpose. Sen’s slope method was used to assess the rate of change, and the Modified Mann–Kendall test was used for the evaluation of the significance of trends in TWS. After, the concept of reliability–resiliency–vulnerability (RRV) was used for assessing the spatial distribution of sustainability in water resources. The results revealed a significant decrease in water availability in the country over the last 15 years. The decrease was found to be highest in the central region where most of the population of the country resides. The reliability in water resources was found high in the northeast Himalayan region and low in the southwest desert; resilience was found low in the central region, while vulnerability was found high in the south and the southeast. Overall, the water resources of the country were found most sustainable in the northeast and southwest and least in the south and the central parts. The maps of water resource sustainability and the changes in water availability produced in the present study can be used for long-term planning of water resources for adaptation to global changes. Besides, those can be used for the management of water resources in a sustainable and judicious manner

Amélioration et désagrégation des données GRACE et GRACE-FO pour l’estimation des variations de stock d’eau terrestre et d’eau souterraine à fine échelle

Abstract : Groundwater is an essential natural resource for domestic, industrial and agricultural uses worldwide. Unfortunately, climate change, excess withdrawal, population growth and other human impacts can affect its dynamics and availability. These excessive demands can lead to lower groundwater levels and depletion of aquifers, and potentially to increased water scarcity. Despite the abundance of lakes and rivers in many parts of Canada, the potential depletion of groundwater remains a major concern, particularly in the southern Prairie. Groundwater is traditionally monitored through in-situ piezometric wells, which are scarcely distributed in Canada and many parts of the world. Consequently, its quantities, distribution and availability are not well known, both spatially and temporally. Fortunately, the launch of the twin satellite systems of Gravity Recovery And Climate Experiment (GRACE) in 2002 and its successor, GRACE Follow-On in 2018 (GRACE-FO) opened up new ways to study groundwater changes. These platforms measure the variations of the Earth's gravity field, which in turn can be related to terrestrial water storage (TWS). The main objective of this thesis is to improve the estimation and spatial resolution of TWS and related groundwater storage changes (GWS), using GRACE and GRACE-FO data. This challenge was addressed through four specific objectives, where original approaches were developed in each case. The first objective was to understand and better take into account the uncertainties associated with the hydrological models (the Global Land Data Assimilation System (GLDAS), and the Water Global Assessment Prognosis hydrological model (WGHM)), generally used in the processing of GRACE or GRACE-FO data. The thesis proposes a new approach based on the Gauss-Markov model to estimate the optimal hydrological parameters from GLDAS, considering six different surface schemes. The Förstner estimator and the best quadratic unbiased estimator of the variance components were used with a least-squares method to estimate the optimal hydrological parameters and their errors. The comparison of the optimal TWS derived from GLDAS to the TWS derived from WGHM showed a very significant correlation of r = 0.91. The correlation obtained with GRACE was r = 0.71, which increased to r = 0.81 when the groundwater component was removed from GRACE. Compared to WGHM and GRACE, the optimal TWS calculated from GLDAS had much smaller errors (RMSE = 7 to 8.5 mm) than those obtained when individual surface schemes are considered (RMSE = 10 to 21 mm); demonstrating the performance of the proposed approach. The second specific objective was to understand regional variations in TWS and their uncertainties. The approach was applied over the Canadian landmass. To achieve the goal, the thesis proposes a new modeling of glacial isostatic adjustment uplift (GIA) in Canada. The comparison of the results of the proposed model and three other existing models with data from 149 very high precision GPS stations demonstrated its superiority in the region considered. The regional approach proposed was then used to extract TWS by correcting the effects of the GIA and leakage. The analyzes showed patterns of significant seasonal variations in TWS, with values ranging between -160 mm and 80 mm. Overall TWS showed a positive slope of temporal variations over the Canadian landmass (+ 6.6 mm/year) with GRACE and GRACE-FO combined. The slope reached up to 45 mm/year in the Hudson Bay region. The third objective was to extract GWS component using a comprehensive rigorous approach to reconstruct, refine and map the variations of GWS and its associated uncertainties. The approach used the methods proposed in the two previous objectives. Moreover, a new filtering approach called Gaussian-Han-Fan (GHF) was developed and integrated into the process in order to have a more robust procedure for extracting information from GRACE and GRACE-FO data. The performance and merits of the proposed filter compared to previous filters were analyzed. Then, the groundwater signal was reconstructed by taking into account all the other components, including surface water variations (estimated using satellite altimetry data). The results showed that the average variations of GWS are between -200 mm and +230 mm in the Canadian Prairies. The maximum and minimum GWS trends were found around the Hudson Bay region (approximately 55 mm/year) and southern Prairies (approximately -20 mm/year), respectively. The error on GWS was around 10% (about 19 mm). The estimated GWS changes were validated using the data from 116 in-situ wells. This validation showed a significant level of correlation (r > |0.70|, P |0.90|, P |0,70|, P |0,90|, P < 10-4, RMSE < 30 mm). Enfin, le dernier objectif consistait à améliorer la résolution spatiale des résultats extraits des données GRACE de 1° à 0.25°. Ainsi, une nouvelle approche basée sur l'ajustement des conditions a d’abord été proposée pour estimer les paramètres hydrologiques optimaux et leurs erreurs. Elle est légèrement différente de la méthode proposée dans le premier objectif. Ensuite, les corrections requises pour extraire les anomalies de TWS et ses incertitudes de manière rigoureuse ont été effectuées suivant la méthodologie présentée à l’objectif 3. Par la suite une nouvelle méthode basée sur la combinaison spectrale-spatiale a été développée pour dériver les anomalies de TWS à échelle réduite (0.25°), en combinant de manière optimale les modèles GRACE et les paramètres hydrologiques. Enfin, les anomalies d’eau souterraines ont été dérivées en utilisant les anomalies de TWS estimées. Les validations ont été faites à partir des données de 75 puits en aquifère non confiné en Alberta. Elles démontrent le potentiel de l’approche proposée avec une corrélation très significative de = 0.80 et un RMSE de 11 mm. Ainsi, la recherche proposée dans la thèse a permis de faire des avancées importantes dans l’extraction d’information sur le stockage total d’eau et les eaux souterraines à partir des données des satellites gravimétriques GRACE et GRACE-FO. Elle propose et valide plusieurs nouvelles approches originales en s’appuyant sur des données in-situ. Elle ouvre également plusieurs nouvelles avenues de recherche, qui permettront de faciliter une utilisation plus opérationnelle de ces types de données à l’échelle régionale, voire locale

Assessment of pluri-annual and decadal changes in terrestrial water storage predicted by global hydrological models in comparison with the GRACE satellite gravity mission

The GRACE (Gravity Recovery And Climate Experiment) satellite gravity mission enables global monitoring of the mass transport within the Earth's system, leading to unprecedented advances in our understanding of the global water cycle in a changing climate. This study focuses on the quantification of changes in terrestrial water storage with respect to the temporal average based on an ensemble of GRACE solutions and two global hydrological models. Significant changes in terrestrial water storage are detected at pluri-annual and decadal timescales in GRACE satellite gravity data that are generally underestimated by global hydrological models though consistent with precipitation. The largest differences (more than 20 cm in equivalent water height) are observed in South America (Amazon, São Francisco and Paraná River basins) and tropical Africa (Congo, Zambezi and Okavango River basins). Smaller but significant (a few centimetres) differences are observed worldwide. While the origin of such differences is unknown, part of it is likely to be climate-related and at least partially due to inaccurate predictions of hydrological models. Pluri-annual to decadal changes in the terrestrial water cycle may indeed be overlooked in global hydrological models due to inaccurate meteorological forcing (e.g. precipitation), unresolved groundwater processes, anthropogenic influences, changing vegetation cover and limited calibration/validation datasets. Significant differences between GRACE satellite measurements and hydrological model predictions have been identified, quantified and characterised in the present study. Efforts must be made to better understand the gap between methods at both pluri-annual and decadal timescales, which challenges the use of global hydrological models for the prediction of the evolution of water resources in changing climate conditions.</p

Agricultural Drought Monitoring And Prediction Using Soil Moisture Deficit Index

The purposes of this study are: 1) to evaluate the performance of an agricultural drought index, Soil Moisture Deficit Index (SMDI) at continental scale; 2) to develop an agricultural drought prediction method based on precipitation, evapotranspiration and terrestrial water storage. This study applied multiple linear regression (MLR) with the inputs of precipitation from Parameter-elevation Regressions on Independent Slopes Model (PRISM), evapotranspiration from Moderate Resolution Imaging Spectroradiometer (MODIS) MOD 16 and terrestrial water storage (TWS) derived from the Gravity Recovery and Climate Experiment (GRACE) to predict soil moisture and SMDI. The inputs of the MLR model were chosen based on the mass conservation of the hydrological quantities at the near surface soil layer (two meters). In addition, the model also includes seasonal and regional terms for estimation. Comparisons with the US drought monitor （USDM）showed that SMDI can be used as a proxy of agricultural drought. The model exhibited strong predictive skills at both one- and two-month lead times in forecasting agricultural drought (correlation \u3e0.8 and normalized root mean square error \u3c15%)

Evaluation of a Model-Based Groundwater Drought Indicator in the Conterminous U.S.

Monitoring groundwater drought using land surface models is a valuable alternative given the current lack of systematic in situ measurements at continental and global scales and the low resolution of current remote sensing based groundwater data. However, uncertainties inherent to land surface models may impede drought detection, and thus should be assessed using independent data sources. In this study, we evaluated a groundwater drought index (GWI) derived from monthly groundwater storage output from the Catchment Land Surface Model (CLSM) using a GWI similarly derived from in situ groundwater observations. Groundwater observations were obtained from unconfined or semi-confined aquifers in eight regions of the central and northeastern U.S. Regional average GWI derived from CLSM exhibited strong correlation with that from observation wells, with correlation coefficients between 0.43 and 0.92. GWI from both in situ data and CLSM was generally better correlated with the Standard Precipitation Index (SPI) at 12 and 24 month timescales than at shorter timescales, but it varied depending on climate conditions. The correlation between CLSM derived GWI and SPI generally decreases with increasing depth to the water table, which in turn depends on both bedrock depth (a CLSM parameter) and mean annual precipitation. The persistence of CLSM derived GWI is spatially varied and again shows a strong influence of depth to groundwater. CLSM derived GWI generally persists longer than GWI derived from in situ data, due at least in part to the inability of coarse model inputs to capture high frequency meteorological variability at local scales. The study also showed that groundwater can have a significant impact on soil moisture persistence where the water table is shallow. Soil moisture persistence was estimated to be longer in the eastern U.S. than in the west, in contrast to previous findings that were based on models that did not represent groundwater. Assimilation of terrestrial water storage data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission improved the correlation between CLSM based regional average GWI and that based on in situ data in six of the eight regions. Practical issues regarding the application of GRACE assimilated groundwater storage for drought detection are discussed. An important conclusion of this study is that model parameters that control the depth to the water table, including bedrock depth, strongly influence the evolution and persistence of simulated groundwater and require careful configuration for drought monitoring

Large-scale assessment of groundwater reserves and processes in Brazil, South America

As reservas de água subterrânea estão entre os componentes do balanço hídrico com maior incerteza de quantificação. O entendimento da sua disponibilidade ainda é limitado em comparação com outras reservas hídricas como rios, atmosfera, solo e lagos. A busca por esse recurso tem aumentado tanto nas áreas úmidas quanto nas áreas secas. Explorar os processos de interação entre as águas subterrâneas e os rios em aquíferos de grande escala (como o comportamento das reservas em períodos secos, eventos de recarga episódica e variabilidade anual), é de grande interesse para a indústria, a economia e a qualidade de vida da população. O desenvolvimento e a avaliação de ferramentas é um passo inicial para o uso sustentável das águas subterrâneas. O objetivo desta tese é avançar no entendimento de processos hidrogeológicos de grande escala que ocorrem no Brasil em diferentes climas e formações aquíferas a partir de ferramentas inovadoras e complementares de monitoramento in situ, dados de sensoriamento remoto e modelagem hidrológica. Verificou-se que o uso do GRACE para detectar variações nas reservas de água subterrânea para um aquífero sedimentar no semiárido brasileiro apresentou resultados adequados. As reservas de água subterrânea estão entre os componentes do balanço hídrico com maior incerteza de quantificação. O entendimento da sua disponibilidade ainda é limitado em comparação com outras reservas hídricas como rios, atmosfera, solo e lagos. A busca por esse recurso tem aumentado tanto nas áreas úmidas quanto nas áreas secas. Explorar os processos de interação entre as águas subterrâneas e os rios em aquíferos de grande escala (como o comportamento das reservas em períodos secos, eventos de recarga episódica e variabilidade anual), é de grande interesse para a indústria, a economia e a qualidade de vida da população. O desenvolvimento e a avaliação de ferramentas é um passo inicial para o uso sustentável das águas subterrâneas. O objetivo desta tese é avançar no entendimento de processos hidrogeológicos de grande escala que ocorrem no Brasil em diferentes climas e formações aquíferas a partir de ferramentas inovadoras e complementares de monitoramento in situ, dados de sensoriamento remoto e modelagem hidrológica. Verificou-se que o uso do GRACE para detectar variações nas reservas de água subterrânea para um aquífero sedimentar no semiárido brasileiro apresentou resultados adequados.Groundwater volumes are among the water balance components with the greatest uncertainty of quantification, the understanding of its availability is still limited compared to other water reserves such as rivers, atmosphere, soil, and lakes. The search for this continuous supply resource throughout the year has increased in wet and dry areas. Exploring hydrological, hydrogeological, and surface-groundwater interaction processes among these large-scale South American aquifers, such as the dynamics associated with dry periods response, recharge events, and interannual variability, is of great interest to the industry, the economy, and the quality of life of the regional population. And the development and testing of tools for researching these aspects is a primer step for sustainable usage of groundwaters in the South American domain. The main objective of this thesis is to advance in the determination of large-scale hydrogeological process in Brazil, South America in different climates and aquifer formations from innovative and complementary tooling of intensive field monitoring, remote sensing data, and hydrological modeling. We found that the use of GRACE to detect variations in groundwater reserves showed adequate results for a small-scale sedimentary aquifer in the Brazilian semi-arid region. The findings were promising to improve the understanding of droughts at different scales in those areas. GRACE data also showed itself as an essential tool for monitoring groundwater volumes in the other two aquifers in humid subtropical areas and investigated in this thesis (Caiuá Aquifer and SASG). We also found that in those humid subtropical areas, the high soil moisture storage has an important role in the occurrence of large episodic recharge events. Atypical rainfall in winter periods was responsible for the increase in soil moisture that explains the larger events. The changes in aquifer storage caused by episodic recharge events are long-lasting and directly affect low flows in rivers with implications on hydro-climatic variability. We also brought important findings related to groundwater variations in fractured aquifer systems, which are complex to predict. Significant contributions related to groundwater level variations, transit times, regional trends, and interaction with the rivers in the SASG were presented