Change maps show a widespread area where drought conditions have degraded 4 Drought Monitor categories in just 4 weeks, a rare occurrence, as flash drought grips the Southern Plains and Ozark Mountains. (Map from U.S. Drought Monitor)Flash drought accelerated by extreme heat in eastern Oklahoma and adjacent states appeared on the U.S. Drought Monitor (USDM) with a one-category-per-week degradation for the last four weeks in a row, as of July 28, 2022 – lightning speed by the standards of drought.
Drought is known as a “creeping phenomenon,” typically coming on over weeks or months that are drier than normal compared with 30 years or more of weather data. But intense heat contributes to faster-emerging drought, particularly at key points in the growing season.
Standard operating procedure for U.S. Drought Monitor authors limits changes to one category per week. “We almost never change the map by more than one category per week, and even seeing it get worse by one category a week for four weeks in a row is unusual,” said Brian Fuchs, one of the USDM authors and head of the National Drought Mitigation Center’s Monitoring program area. “Plus, this was an unusually large area.”
When the USDM does change by more than one category in a week, it’s more often in the direction of improvement. Multi-category changes happen most frequently when a hurricane or tropical storm brings heavy rains or flooding to a drought-stricken area. Flooding may not be welcome, but it can lead to a multi-category improvement on the USDM, sometimes within a single week. In comparison, multi-category degradations over short periods, like what’s happening in Oklahoma and elsewhere right now, are less common.
Since the early 2000’s, drought researchers have referred to fast-emerging drought driven by heat as “flash drought,” although it does not have a precise definition, Fuchs said. A two- or three-class change in four weeks could also be a flash drought.
The USDM is a weekly map showing the location and intensity of drought, updated every Thursday morning based on data through the previous Tuesday. The USDM puts each part of the country in one of six categories: None, Abnormally Dry (D0), Moderate Drought (D1), Severe Drought (D2), Extreme Drought (D3) or Exceptional Drought (D4).
The combination of heat and dryness causes hardship for agricultural producers. The USDM triggers eligibility for some U.S. Department of Agriculture programs, but the map is based on data about physical indicators. The USDA uses the map as an independent, objective scientific tool to implement their programs.
The U.S. Drought Monitor website includes several ways to visualize drought over time:
To let USDM authors and others know how dry, wet or normal conditions look in your part of the country, please submit Condition Monitoring Observer Reports (CMOR), which can include photos. CMOR reports become part of a historic record, and in the short-term, they can help call USDM authors’ attention to areas that are changing rapidly.
Learn more about the making of the USDM map.
The Drought Center’s website provides extensive information about drought and drought planning.
-- NDMC Communications