The goal of this project is expand our suite of weekly drought/wetness indicators to include 1-3 month forecasts for the continental U.S., which will then be utilized by our partners at the National Drought Mitigation Center (NDMC), the NOAA North Central River Forecast Center (NCRFC), and the U.S. Army Corps of Engineers (USACE). The current indicator suite comprises wetness percentiles of shallow groundwater and surface and root zone soil moisture. The underlying land surface model simulation integrates high quality meteorological data and assimilates Gravity Recovery and Climate Experiment (GRACE) satellite-based terrestrial water storage observations. The results are served from the NDMC website (http://drought.unl.edu/MonitoringTools/NASAGRACEDataAssimilation.aspx) and used as input to the U.S. Drought Monitor, which is the premier drought product for the U.S. Because deep soil moisture and groundwater have long memories (they change slowly in response to meteorological conditions), GRACE data have an important and lasting impact on the land surface model simulation. The GRACE data themselves are enhanced through synthesis with high resolution meteorological data constrained by land surface model physics. We will extend the value of GRACE and GRACE Follow On (GRACE FO) satellite-based observations three months into the future by driving the same land surface model with forecast meteorological data, taking advantage of the groundwater and soil moisture memory and making use of new low-latency GRACE hydrology products. Three types of meteorological forcing in the forecast period are being tested: (1) meteorological fields drawn from GEOS-5 forecast and downscaled to North American Land Data Assimilation System phase 2 (NLDAS-2) resolution (12.5km) through Bayesian merging with historical NLDAS-2 fields; (2) a hybrid statistical-dynamical meteorological forecast generated through analog downscaling, in which large scale atmospheric fields from the GEOS-5 forecast are pattern-matched to days in the historic GEOS-5 archive and meteorological fields are drawn from NLDAS for those analog dates; and (3) as the control, “null forecast” simulations that are driven by climatology in the forecast period. The simulations are performed both with and without GRACE data assimilation in the retrospective period in order to gauge its impact. Further, we will quantify the contribution of each aspect of the forecast system—memory in the land surface model, GRACE data assimilation, GEOS-5 forecast meteorology, and GEOS-5 forecast of large scale atmospheric patterns—to skillful prediction of drought and flood. The best performing configuration will be used for the final forecast system. We expect that the low latency GRACE terrestrial water storage data, which were developed under the direction of one of the co-investigators and are being tested by this project, will greatly increase the potential for GRACE and GRACE FO to add value to the forecasts. Our team includes partners from NDMC, NOAA NCRFC, and USACE, who will distribute, test, and make use of the resulting 30-90 day forecasted, 0.125° gridded groundwater, soil moisture, snow, and other fields and associated wetness indicators. Considering the strength of our team, our connections to the broader drought, river flow, and flood communities, and our past success in delivering high quality wetness indicators which have been embraced by the drought community, we believe the forecast data that result from this project will be quickly adopted by and highly valuable to end users. An assessment of the value of the information to end users is being led in parallel by our partners at Resources for the Future (RFI).

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