Impact of soil-moisture/terrestrial water-storage assimilated initializations on forecasting drought

Two sets of monthly-initialized 9-month forecasts were produced with and without the assimilation of soil moisture/terrestrial water storage to study the role of assimilation on drought prediction skill in Horn of Africa (HOA: 21.25E-51.25E; 11.25S-23.75N) and TEXas-MEXico region (TEXMEX: 111.25W-86.25W; 18.75N-41.25N). The non-assimilated (CTL) hydrological forecasts were produced with catchment land-surface model (CLSM-f2.5) being run as a land-component within a coupled general circulation model - Goddard Earth Observing System Model, Version 5 (GEOS5). The assimilation (EXP) forecasts were produced by running the CLSM-f2.5 in off-line mode and by assimilating (i) top-layer soil moisture from Advanced Microwave Scanning Radiometer – EOS (AMSR-E) and (ii) terrestrial water storage from Gravity Recovery And Climate Experiment (GRACE). In the assimilated runs, the atmospheric forcing used were obtained from CTL forecasts. The differences in severity and spatial extension of the drought in the year 2011 is analyzed between CTL and EXP forecasts using standardized soil wetness and standardized runoff indices. The standardized indices along with quantitative and categorical skill metrics highlight the impact of assimilated forecast-initializations on extending the drought skill beyond a month.