Abstract
Changes in the climate and population growth will critically impact the future supply and demand of water, leading to large uncertainties for sustainable resource management. In the absence of on-the-ground measurements to provide spatially continuous, high-resolution information on water supplies, satellite observations can provide essential insight. Here, we develop a technique using observations from the Gravity Recovery and Climate Experiment (GRACE) satellite to evaluate the sustainability of surface water and groundwater use over the continental United States. We determine the annual total water availability for 2003–2015 using the annual variability in GRACE-derived total water storage for 18 major watersheds. The long-term sustainable water quantity available to humans is calculated by subtracting an annual estimate of the water needed to maintain local ecosystems, and the resulting water volumes are compared to reported consumptive water use to determine a sustainability fraction. We find over-consumption is highest in the southwest US, where increasing stress trends were observed in all five basins and annual consumptive use exceeded 100% availability twice in the Lower Colorado basin during 2003–2015. By providing a coarse-scale evaluation of sustainable water use from satellite and ground observations, the established framework serves as a blueprint for future large-scale water resource monitoring.
Highlights
The ability to sustainably manage water resources to avoid long-term depletion or environmental harm is of increasing importance due to the numerous alarming observations of diminishing global freshwater resources[1,2,3,4]
In some cases the estimates of water availability do not account for the total amount of water that is available to a given area due to, for example, inter-basin water transfer and deep groundwater storage, with some studies omitting groundwater resources from the analysis completely[5]
Consideration of ecosystem requirements is often missing[23]. We address these deficiencies by developing a comprehensive method that relies on satellite observations to compare total water availability (TWA), including all available aboveground and belowground water, to consumptive water use
Summary
Data used to calculate TWS came from the Gravity Recovery and Climate Experiment (GRACE) satellite mission[24]. Basin-distributed environmental coefficients are applied to account for the portion of the resulting volume that must remain in the environment to minimize damage to the ecosystem It is assumed the residual water must stay in the environment in the form of stored surface water and groundwater to be available for environmental use. Given the known uncertainty in the environmental coefficient and irrigation efficiency parameter values, a parameter sensitivity analysis in Supplementary Table 1 was used to present the mean annual consumptive water use to availability ratios calculated using Equation 3. Both parameters were allowed to vary by +/−0.15 to assume a standard sigma range. This data is available for download at the NASA Land Data Assimilation Systems website (http:// ldas.gsfc.nasa.gov/nldas/NLDAS2model_download.php)
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