North American Drought Briefing
This web site presents the current hydro-climate conditions, objective drought assessment over the United States for the recent week, calendar month and three month season. This activity supports the operational National Drought Monitor and National Drought Outlook. An objective way to classify drought is to use drought indices. For meteorological drought, the Standardized Precipitation Index (SPI) is used to measure precipitation deficits. The Standardized Runoff Index (SRI), similar to the SPI, is used to classify hydrological drought. Agricultural drought is measured by monthly mean soil moisture (SM) anomaly percentiles based on probability distributions. The runoff, soil moisture and hydrological variables are based on the products from the North American Data Assimilation. Products from each individual model (Noah, Mosaic, VIC and SAC) and the multi- model ensemble are presented. The atmospheric variables are based on the North American Regional Reanalysis. Anomalies are computed with respect to a common base period 1979-2007. The regional hydrologic section presents area averaged time series of hydrological variables for the recent period for each River Forecast Center.