US Drought Monitor

The US Drought Monitor maps are based on expert synthesis of drought indicators including (but not limited to) the Palmer Drought Severity Index, soil moisture, streamflow, precipitation, and measures of vegetation stress, as well as reports of drought impacts. The USDM categories are assigned so that they generally correspond with one or more of the objectively measured indicators, listed above, being in these percentile classes:

D0 (abnormal dryness) – 20th-30th percentile
D1 (moderate drought) – 10th-20th percentile
D2 (severe drought) – 5th-10th percentile
D3 (extreme drought) – 2nd-5th percentile
D4 (exceptional drought) – 0th-2nd percentile

The USDM is produced in partnership between the National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln, the United States Department of Agriculture, and NOAA. The US Drought Monitor is released weekly (every Thursday) by the NDMC, and it represents data collected through that Tuesday. Both academic and government drought experts participate in weekly calls to discuss changes to the forthcoming USDM, and this input is compiled by the author(s) named on each week’s map. 

The weekly state USDM maps for Colorado, Utah, and Wyoming show the same drought categories and boundaries as the nationwide map, but at a higher spatial resolution and with the county boundaries shown, so that local conditions can be more easily discerned. 

Each USDM is released with a text discussion that provides supporting detail on drought conditions in different parts of the country.