Monitoring Drought

 The Standardized Precipitation Index

Current Standardized Precipitation Index maps showing SPI data over the previous 1, 3, 6, 9, and 12 months. A current year-to-date map is also provided.

2008 SPI maps through March

Archived SPI Maps

The Standardized Precipitation Index (SPI) is a relatively new drought index based only on precipitation. The SPI can be used to monitor conditions on a variety of time scales. This temporal flexibility allows the SPI to be useful in both short-term agricultural and long-term hydrological applications. The NDMC’s overview of drought indices contains an in-depth look at the SPI.

The SPI was developed by T.B. McKee, N.J. Doesken, and J. Kleist and in 1993. The data and climate division boundaries are from the National Climatic Data Center. The Western Regional Climate Center uses the NCDC data to calculate SPI values for each climate division. The information is then reclassed and mapped at the National Drought Mitigation Center using a Geographic Information System. The maps are based on preliminary precipitation data, and the data’s source and methods used in incorporating the data into a final product must be considered carefully when analyzing these maps. “Interpretation of SPI Maps” explains how to interpret the maps at various timescales. Download the SPI program and examples here.

Look for monthly updates of these maps around the 15^th of each month.