Alternative predictors for forecasting drought conditions over Continental United States

The prediction skill of climatological and agricultural drought episodes on seasonal timescales in Climate Forecast System Reanalysis (CFSR) and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) is analyzed using vertically integrated moisture transport (VIMT) and moisture flux convergence (MFC) over the continental United States (CONUS). The climatological precipitation conditions that influence the VIMT and MFC, which in turn represent the prediction skill of the extent and the severity of the drought episodes in Southeast (2007-2008) and Great Plains (2011) are analyzed for the genesis, growth and decay phases of the drought. The dominant patterns of VIMT and MFC that explain about 90% of the spatial variance are extracted using empirical orthogonal function (EOF) analysis and the drought patterns based on reconstructed data are compared with the 3- and 6-M standardized precipitation indices (SPIs) of Climate Prediction Center (CPC) unified gauge-based optimally interpolated objective analysis dataset and soil moisture percentiles of North American Land Data Assimilation System (NLDAS). Our analysis suggests that the reliability of MFC as an indicator of climatological or agricultural drought is based on the relative importance of the evapotranspiration contribution and the VIMT compliments MFC as a climatological drought indicator on seasonal timescales. These findings are extended to seasonal forecasts of CFSv2 and GEOS5 to evaluate the efficacy of VIMT and MFC as alternatives to precipitation and soil moisture based drought indices at 3- and 6-month lead times. The relatively robust prediction skill of large-scale circulation in the coupled general circulation models renders VIMT and MFC as attractive alternatives to traditional drought indicators based on precipitation and soil moisture.