GRACE Science Team Meeting

B.5.1 to B.5.8 - Hydrology
(Convener: )

Using GRACE to validate Noah-MP water budget simulations in the Mississippi River Basin
(X. Cai, Z-L. Yang)

GRACE satellite monitoring of large depletion in water storage in response to the 2011 drought in Texas
(D. Long, B. R. Scanlon, L. Longuevergne)

Gravity changes over Russian rivers basins from GRACE
(L. Zotov, N. Frolova, M. Harlamov)

Groundwater depletion in North China from GRACE satellites, ground-based monitoring network and groundwater modeling
(W. Feng, M. Zhong, J-M. Lemoine, R. Biancale, H.T. Hsu, J. Xia, C.M. Zheng, G.L. Cao, Q.H. Tang)

Integrated Approach to Address the Temporal Changes in the Saharan and Arabian Aquifers in Response to Climatic and Anthropogenic Forces
(M. Sultan, M. Ahmed, J. Wahr, E. Yan)

Terrestrial water dynamics over the Congo Basin from GRACE and other remote sensing measurements
(H. Lee, C. Shum Second, D. Alsdorf Third, E. Beighley Fourth, J. Duan Fifth, H. Jung Sixth, T. Yuan Seventh, R. Roufi Eighth)

Hydrological Mass Variations Caused by Extreme Weather Conditions in Yangtze River Basin Measured by GRACE and Connections with ENSO
(Z. Zhang, B. F. Chao, J.L. Chen, C.R. Wilson)

The value of GRACE TWS data in improving CLM4 snow mass
(Y. Zhang, H. Su, Z-L. Yang, T. Hoar, J. Anderson)


Potential impacts of climate and environmental change on the stored water of Lake Victoria Basin and economic implications
(A. Awange, R. Anyah, N. Agola, E. Forootan, P. Omondi )

Total and ground water storage variations from 10-year GRACE observations in Canada
(J. Huang, G. Pavlic, S. Wang, A. Rivera, J. Henton, A. Lambert, C. Klatt)

Title: Using GRACE to validate Noah-MP water budget simulations in the Mississippi River Basin
Presenter: Yang, Z-L.
Co-Authors: X. Cai; Z-L. Yang

Abstract: The Gravity Recovery and Climate Experiment (GRACE) derived terrestrial water storage (TWS) is now more and more used in validating the performance of land surface models (LSMs) in TWS simulations, which indicate how well LSMs can represent the general water cycle. This study uses the GRACE-derived TWS to evaluate the newly developed community Noah LSM with multiparameterization options (Noah-MP) in the Mississippi River Basin (MRB). The Noah-MP model is driven by the North American Land Data Assimilation System Phase 2 (NLDAS-2) atmospheric forcing. The spatial resolution is 1/8th-degree and the temporal resolution is hourly. Results show that: (1) Noah-MP simulated TWS anomaly, not only the timing but also the magnitude of water fluctuation, is consistent with GRACE-derived TWS anomaly, which indicates that Noah-MP is doing a good job in representing the overall water cycle. (2) For the entire MRB, the largest contribution of TWS anomaly is from soil moisture, the second largest is groundwater, and the third is snow. (3) Noah-MP is capable to represent the natural processes; however, it still has difficulty in capturing the signals from the anthropogenic influences. (4) Among the flux terms (precipitation, ET, and runoff), the cumulative anomaly of ET has the largest variation amplitude, which makes it the dominant water flux in driving the TWS anomaly.

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Title: GRACE satellite monitoring of large depletion in water storage in response to the 2011 drought in Texas
Presenter: Long, Di
Co-Authors: B. R. Scanlon; L. Longuevergne

Abstract: Texas experienced the most extreme one-year drought on record in 2011 with precipitation at 40% of long-term mean and agricultural losses of ~$7.6 billion. We assess the value of Gravity Recovery and Climate Experiment (GRACE) satellite-derived total water storage (TWS) change as an alternative remote sensing-based drought indicator, independent of traditional drought indicators based on in situ monitoring. GRACE shows depletion in TWS of 62.3 ± 17.7 km3 during the 2011 drought. Large uncertainties in simulated soil moisture storage depletion (14-83 km3) from six land surface models indicate that GRACE TWS is a more reliable drought indicator than disaggregated soil moisture or groundwater storage. Groundwater use and groundwater level data indicate that depletion is dominated by changes in soil moisture storage, consistent with high correlation between GRACE TWS and the Palmer Drought Severity Index. GRACE provides a valuable tool for monitoring statewide water storage depletion, linking meteorological and hydrological droughts. Trend analysis of TWS filtered by the seasonal, moving average, and Butterworth (0.05) filters indicates that TWS decreases at rates ranging from -11.5±1.2 mm/a for seasonal filter to -14±0.4 mm/a for the Butterworth filter.

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Title: Gravity changes over Russian rivers basins from GRACE
Presenter: Zotov, Leonid
Co-Authors: L. Zotov; N. Frolova; M. Harlamov

Abstract: GRACE twin-satellites provide monthly data upon the gravitational field of the Earth since 2003, what presents a big interest for hydrological studies. Gravity data reflect changes, related to the groundwater redistribution, ice melting, and precipitation accumulation.

We use Multichannel Singular Spectrum Analysis to filter GRACE data and separate the principal components (PCs) of different periods. The obtained animated maps of PCs are useful for seasonal and long-periodic gravity changes study. Data averaging over the large river basins of Russia was performed. The obtained curves can be compared to the hydrological models, such as GLDAS or WGHM.

By spring 2013 an extremely large snow accumulation occurred in Russia. Melting of this snow induced large floods and river levels increase. The exceptional maxima are well seen in the curves obtained from GRACE.

Speaking about long-periodic climate-related changes, they are different for the basins of European and Siberian rivers. Overall trend represents maximum in 2009, following by slow decrease. Possible reasons of this are discussed.

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Title: Groundwater depletion in North China from GRACE satellites, ground-based monitoring network and groundwater modeling
Presenter: Feng, Wei
Co-Authors: M. Zhong; J-M. Lemoine; R. Biancale; H.T. Hsu; J. Xia; C.M. Zheng; G.L. Cao; Q.H. Tang

Abstract: Extensive anthropogenic activities in North China, such as agricultural irrigation and urbanization, are depleting the groundwater resource in the region at an alarming rate. Since its launch in 2002, the Gravity Recovery and Climate Experiment (GRACE) satellites have become a powerful tool to monitor regional groundwater storage change. This paper provides a detailed assessment of spatiotemporal variations of groundwater in North China, as estimated from three relatively independent methods, i.e., GRACE satellite measurements, ground-based well observations, and regional groundwater modeling. First we calculated the groundwater storage changes in the region by combining the time-varying gravity field data from GRACE with outputs from land-surface models. Besides the natural surface-water storage component, the effects of reservoir storage, coal transport and inter-basin water diversion in the region were also assessed and removed from GRACE-derived terrestrial water storage changes. The spatial pattern of GRACE-based groundwater depletion indicates significant water mass loss in the piedmont and central plain regions of North China. The ground-based monitoring well network also indicates that the water table in the piedmont regions of Taihang Mountains, the western part of North China Plain, declines faster than those in other regions of North China. This is in good agreement with the GRACE-based result. Then, we built a multilayer regional groundwater model to simulate the flow system in the North China Plain. Simulated groundwater depletion further confirms the GRACE-derived result, i.e., the large groundwater depletion rate exists in the piedmont region of North China.

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Title: Integrated Approach to Address the Temporal Changes in the Saharan and Arabian Aquifers in Response to Climatic and Anthropogenic Forces
Presenter: Sultan, Mohammed
Co-Authors: M. Ahmed; J. Wahr; E. Yan

Abstract: Monthly (January 2003 - September 2012) Gravity Recovery and Climate Experiment (GRACE) gravity field solutions were processed, analyzed and spatially and temporally correlated with other relevant datasets in a Geographic Information System (GIS) environment over the Nubian Sandstone Aquifer System (NSAS) and the Arabian Peninsula Aquifer System (APAS). Examination of the GRACE-derived Terrestrial Water Storage (TWS) trends revealed two areas of significant TWS depletions, the first area correlated with the Dakhla Aquifer System (DAS) within the NSAS and second with the Saq Aquifer System (SAS) in the APAS. Annual GRACE-derived groundwater depletion rates were estimated at 2.04 ± 0.99 cubic kilometers and 6.11 ± 1. 83 cubic kilometers for the DAS and the SAS, respectively. Findings include (1) excessive groundwater extraction, not climatic changes, is responsible for the TWS depletion over the DAS and the SAS ;(2) the DAS available reserves could be consumed in 300 years if the current extraction rates continue to double every 50 years and those for the SAS could be consumed within 70-160 years at present extraction and depletion rates; and (3) observed depletions over DAS and SAS and their absence across the remaining regions of the NSAS and the APAS suggest the aquifers are at near-steady conditions except for the DAS and SAS that are witnessing unsteady transient conditions. Implications for applying the methodologies advocated for assessment and optimum management of a large suite of fossil aquifers worldwide are clear.

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Title: Terrestrial water dynamics over the Congo Basin from GRACE and other remote sensing measurements
Presenter: Lee, Hyongki
Co-Authors: H. Lee; C. Shum Second; D. Alsdorf Third; E. Beighley Fourth; J. Duan Fifth; H. Jung Sixth; T. Yuan Seventh; R. Roufi Eighth

Abstract: The Congo Basin is the world's third largest in size (~3.7 million km2), and second only to the Amazon River in discharge (~40,200 m3 s−1 annual average). However, the hydrological dynamics of seasonally flooded wetlands and floodplains remains poorly quantified. Here, we separate the entire Congo wetlands into four 3°×3° regions, and use GRACE, other remote sensing measurements (satellite radar altimeter, GPCP, GRFM mosaics), and the Hillslope River Routing (HRR) model to estimate the amounts of water filling and draining from the Congo wetlands, and to determine the source of the water. We find that the amount of water annually filling and draining the Congo wetlands is 111 km3 (summing all four study regions), which is about one-third the size of the water volumes found on the mainstem Amazon floodplain. Based on amplitude comparisons among the water volume changes and timing comparisons among their fluxes, we conclude that the local upland runoff is the main source of the Congo wetland water, not the fluvial process of river-floodplain water exchange as in the mainstem Amazon floodplain. Our hydraulic analysis using altimeter measurements also supports our conclusion by demonstrating that water surface elevations in the wetlands are consistently higher than the adjacent river water levels.

Next, we attempt to decompose the total water storage (TWS) over the central Congo Basin from GRACE data into its surface and subsurface components by first estimating the surface water storage changes from a combination of water level changes from Envisat altimetry and inundated extent changes from PALSAR ScanSAR images. Here the GRACE TWS is estimated using the Level 2 monthly Stokes coefficients and decorrelation, filtering and considerations of signal leakage and other corrections, with the near future efforts to also employ regional gravity field inversion. We use Envisat altimetry to determine an optimal threshold to classify flooded areas from the Scan SAR images. The estimated surface storage changes are then subtracted from the GRACE total TWS to infer the subsurface storage changes over the central Congo. Our result indicates that the annual variations of the TWS changes during the period of 2007 - 2010 range between 21 km3 and 31 km3, and mostly controlled by surface storage changes. Our result is in contrast with a study over another large tropical basin, the Negro River Basin, where the amplitude of the subsurface storage changes represents more than a third of the amplitude of TWS changes. Our findings contribute to providing a basis for improved determination and potential prediction of impacts resulting from climate change and deforestations on the distribution of terrestrial water stores and fluxes in the Congo Basin.

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Title: Hydrological Mass Variations Caused by Extreme Weather Conditions in Yangtze River Basin Measured by GRACE and Connections with ENSO
Presenter: Zhang, Zizhan
Co-Authors: Z. Zhang; B. F. Chao; J.L. Chen; C.R. Wilson

Abstract: Droughts caused by extreme weather conditions, occur frequently in the Yangtze River basin, and directly affect terrestrial water storage change. Launched in March 2002, the dual-satellite mission of the Gravity Recovery and Climate Experiment (GRACE) has enabled the measurement of the Earth's time-variable gravity (TVG), which provides a new measure of mass transport in the Earth system, including short periodic hydrological mass variations. In the summer of 2006 and spring of 2011, the upper and middle-lower stream of the Yangtze River experienced two worst drought events in the last 50 years. Here, we examine terrestrial water storage (TWS) changes over the Yangtze River basin caused by the two extreme weather events using GRACE RL05 TVG data and predications from major land surface models and other measurements, including TWS estimates from the global land data assimilation system (GLDAS) and WaterGAP Global Hydrology Model (WGHM), and precipitation from the Tropical Rainfall Measuring Mission (TRMM) and river gauge data. The extension and intensity of these two severe droughts are clearly observed by GRACE, and GRACE is apparently doing a better job than hydrological models do in catching up these two climate events. The results demonstrate the unique potential of GRACE measurements in monitoring large-scale hydrological mass variation events and in evaluating advanced climate and land surface models. The correlation and coherence between TWS changes in the Yangtze River basin and ENSO index are significant at non-seasonal scales, indicating a strong connection between ENSO events and climate change in the Yangtze River basin.

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Title: The value of GRACE TWS data in improving CLM4 snow mass
Presenter: Zhang, Yongfei
Co-Authors: Y. Zhang; H. Su; Z-L. Yang; T. Hoar; J. Anderson

Abstract: The Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage (TWS) anomaly data are assimilated into the Community Land Model version 4 (CLM4) via the Data Assimilation Research Testbed (DART) to improve the snow mass estimate on global scales. A freely available ensemble of reanalysis data created by DART and the Community Atmospheric Model (CAM4.0) is used as the meteorological forcing for each CLM ensemble member. This ensemble forcing induces a spread in the CLM ensemble during a spin-up phase and helps maintain the spread during the assimilation. Spatially-varying TWS errors available from the CSR GRACE RL05 are used in this work.

The joint Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover and GRACE TWS assimilations are compared with the open loop run and the model run that assimilates the MODIS snow cover data only. The MODIS snow cover data assimilation has limitations when snow cover reaches 100%, while the GRACE TWS data assimilation can adjust model snowpack as long as the snow mass changes. Improvements over the MODIS-only model run are noteworthy in the high latitudes where the MODIS snow cover data can hardly influence the model. Exceptions exist in the western Siberia, which is attributed to the small model uncertainty in this region. Supplemental algorithms are planned to inflate the model ensemble spread.

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Title: Potential impacts of climate and environmental change on the stored water of Lake Victoria Basin and economic implications
Presenter: Awange, Joseph
Co-Authors: R. Anyah; N. Agola; E. Forootan; P. Omondi

Abstract: The changing climatic patterns and increasing human population within the Lake Victoria Basin (LVB), together with overexploitation of water for economic activities call for assessment of water management for the entire basin. This study focused on the analysis of long historical record of in-situ climate data, Gravity And Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) observations, and high resolution Regional Climate Models (RCMs), over recent decade(s) to assess the water storage changes within the basin linked to recent climatic variability/changes and anomalies. We employed trend analysis, principal component analyses (PCA), and temporal/spatial correlations to explore the associations among LVB stored water, rainfall variability, and large scale forcings associated with El-Nino/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Potential economic impacts of changes in LVB stored water influenced by climate and environmental changes are also explored.

The observed in-situ rainfall showed a general increasing trend that was insignificant at 95% confidence level. The dominant patterns of rainfall data from the TRMM suggest that precipitation conditions have not changed much during the period of 1998-2012 over the basin. Over LVB, GRACE's water storage changes indicate an average decline of 38.2 mm/yr for 2002-2006, likely due to the extension of the Owen dam, and an increase of 4.5 mm/yr over 2007-2013, likely due to two massive rainfalls in 2006-2007 and 2010-2011. The temporal correlations between rainfall and ENSO/IOD indices during the study period, based on TRMM and RCMs, suggest significant influence of large scale forcing on LVB rainfall, and thus stored water.

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Title: Total and ground water storage variations from 10-year GRACE observations in Canada
Presenter: Huang, Jianliang
Co-Authors: G. Pavlic; S. Wang; A. Rivera; J. Henton; A. Lambert; C. Klatt

Abstract: Inter-annual and seasonal variations in total and ground water storage are functions of rainfall, rates of runoff and evapotranspiration as well as soil moisture and ground water storage capacity. Total storage changes are indicative of the magnitudes of the annual and inter-annual water cycles in Canada and its major river basins. In this study, we aim to quantify inter-annual total and ground water storage (TWS and GWS) variations in three Canadian river basins (Mackenzie, Saskatchewan and Assiniboine), and seasonal variation in Canada using Release 5's monthly Earth's gravity models derived from GRACE (Gravity Recovery And Climate Experiment satellite mission) observations by the CSR, University of Texas, USA for the period of 2003-2012. The national TWS and GWS variations are shown as four seasonal maps of the GRACE-only and the GRACE-combined with GLDAS NOAH model for Jan.-Mar., Apr.-Jun., Jul.-Sept., and Oct.-Dec. averaged over 2003-2012. The inter-annual TWS and GWS variations for the three basins are shown as 10-year water-thickness-equivalent time series representing average water storage anomalies over the respective basins. The GRACE satellites do not directly observe the GWS variation, which needs to be separated from the GRACE TWS variation by removing surface water (SW) storage components: soil moisture, snow and ice, lake and river water storage variations. For the GWS separation, we use the SW storage variations predicted by the US NASA's Global Land Data Assimilation System (GLDAS) NOAH model and the NRCan's Ecological Assimilation of Land and Climate Observations (EALCO) model.

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