Predicting Global Drought Conditions Using the North American Multi-Model Ensemble

The 14th Weather Squadron (14WS) is the Department of Defense (DoD)’s organization responsible for delivering climate information and services to DoD entities. Of increasing importance is characterization of drought conditions, not only for analysis, but also for monthly drought forecasts out to 5 months. In order to optimize characterization of the global environment using one standard, 14WS evaluates the Stanadardized Precipitation Index (SPI) developed by McKee et al. (1993) using monthly precipitation from the Global Precipitation Climatology Centre (Schneider et al. 2011) against both the Standardized Precipitation Evapotranspiration Index (SPEI) (Vicente-Serrano et al. 2010) and the Palmer Drought Severity Index (Alley et al. 1984). To create the forecasts, we add the North American Multi-Model Ensemble (Kirtmann et al. 2014) precipitation anomaly forecasts to a 30 year precipitation climatology and then compute the SPI values for the forecast months. Two years of verification statistics show consistent improvement over persistence for all forecast lead times. However, there is a significant bias that reduces drought coverage and intensity as the forecast lead increases. Preliminary investigation shows that there is a wet bias in the precipitation forecasts for areas that have an ongoing drought. Continued work includes implementation and testing on a regional scale considering the unique requirements of the DoD.