Abstract
Since March 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided first estimates of land water storage variations by monitoring the time‐variable component of Earth's gravity field. Here we characterize spatial‐temporal variations in terrestrial water storage changes (TWSC) from GRACE and compare them to those simulated with the Global Land Data Assimilation System (GLDAS). Additionally, we use GLDAS simulations to infer how TWSC is partitioned into snow, canopy water and soil water components, and to understand how variations in the hydrologic fluxes act to enhance or dissipate the stores. Results quantify the range of GRACE‐derived storage changes during the studied period and place them in the context of seasonal variations in global climate and hydrologic extremes including drought and flood, by impacting land memory processes. The role of the largest continental river basins as major locations for freshwater redistribution is highlighted. GRACE‐based storage changes are in good agreement with those obtained from GLDAS simulations. Analysis of GLDAS‐simulated TWSC illustrates several key characteristics of spatial and temporal land water storage variations. Global averages of TWSC were partitioned nearly equally between soil moisture and snow water equivalent, while zonal averages of TWSC revealed the importance of soil moisture storage at low latitudes and snow storage at high latitudes. Evapotranspiration plays a key role in dissipating globally averaged terrestrial water storage. Latitudinal averages showed how precipitation dominates TWSC variations in the tropics, evapotranspiration is most effective in the midlatitudes, and snowmelt runoff is a key dissipating flux at high latitudes. Results have implications for monitoring water storage response to climate variability and change, and for constraining land model hydrology simulations.
Highlights
[16] Figure 1a shows that the time series of globally averaged terrestrial water storage changes (TWSC) peaks during NH Winter (DJF) with an amplitude of roughly 0.6 centimeters/month
The polar regions are similar to the tropics, but with slight JJA (DJF) increases in TWSC, in the NH
[44] Global, zonal and basin-scale estimates of GRACEbased storage changes showed a wide range in variability and magnitude, emphasizing the space-time heterogeneity in TWSC response
Summary
[2] Terrestrial water storage (TWS) is defined as all forms of water stored above and underneath the surface of the Earth. [5] Most GRACE hydrology studies to date, including those described above and in section 2 below, have dealt with either comparison of derived terrestrial water storage anomalies (TWSA, i.e., TWS deviations from the mean rather than month to month changes) to models and to limited observations; methods of data processing and error analyses; and to new applications for monitoring TWS components and fluxes. While the capability for GRACE to monitor continental scale anomalies and changes in monthly water storage is well documented, little if any work has addressed fundamental issues such as the characterization of its space-time variability and its role in terrestrial hydroclimatology, namely how observed TWSC is distributed among the terrestrial subsurface and surface stores, and how the fluxes of precipitation, evapotranspiration and runoff act to enhance or dissipate the storages. Having demonstrated good agreement between the two, in the third part of the analysis, we discuss the zonal and global patterns of variability in TWSC and how these patterns are controlled by the various hydrologic and climatologic factors, using GLDAS-based states and fluxes
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