Toward Integrating Enhanced Grace Terrestrial Water Storage Data Into The U.S. And North American Drought Monitors

摘要

NASA's Gravity Recovery and Climate Experiment(GRACE) satellites measure time variations of the Earth'sgravity field enabling reliable detection of spatio‐temporalvariations in total terrestrial water storage (TWS), includinggroundwater. The U.S. and North American DroughtMonitors are two of the premier drought monitoringproducts available to decision‐makers for assessing andminimizing drought impacts, but they rely heavily onprecipitation indices and do not currently incorporatesystematic observations of deep soil moisture andgroundwater storage conditions. Thus GRACE has greatpotential to improve the Drought Monitors by filling thisobservational gap. Horizontal, vertical and temporaldisaggregation of the coarse‐resolution GRACE TWS data hasbeen accomplished by assimilating GRACE TWS anomaliesinto the Catchment Land Surface Model using an ensembleKalman smoother. The Drought Monitors combine severalshort‐term and long‐term drought indices and indicatorsexpressed in percentiles as a reference to their historicalfrequency of occurrence for the location and time of year inquestion. To be consistent, we are in the process ofgenerating a climatology of estimated soil moisture andground water based on a 60‐year Catchment modelsimulation which will subsequently be used to convert sevenyears of GRACE assimilated fields into soil moisture andgroundwater percentiles, for systematic incorporation intothe objective blends that constitute Drought Monitorbaselines. At this stage we provide a preliminary evaluationof GRACE assimilated Catchment model output againstindependent datasets including soil moisture observationsfrom Aqua AMSR‐E and groundwater level observations fromthe U.S. Geological Survey's Groundwater Climate ResponseNetwork.