If you are a regular visitor to this website, you have probably seen the weekly reports on drought conditions locally and in the rest of Georgia. How is the information that goes into producing those reports gathered?
Here’s an explanation from drought.gov: and several other sources:
How the U.S. Drought Monitor Determines Weekly Drought Status
The U.S. Drought Monitor (USDM) is a weekly map updated every Thursday that shows the location and severity of drought across the United States and its territories. It uses a five-category system (Abnormally Dry D0, Moderate D1, Severe D2, Extreme D3, Exceptional D4) to reflect how unusual current dryness is for a given location and season Drought.gov+1.
Data Sources and Indicators
The USDM is not a single-statistics model—it’s a “convergence of evidence” approach that blends physical climate, weather, and hydrological data with drought impacts and local expert input U.S. Drought Monitor+1. Key data include:
- Precipitation (recent and long-term deficits/surpluses)
- Temperature and evaporative demand
- Soil moisture
- Streamflow and reservoir levels
- Lake and river water levels
- Snow cover and meltwater runoff
- Vegetation health
- Drought impacts such as water shortages, business interruptions, and wildfire risk Drought.gov+2
These are often ranked by percentiles to show how rare the current conditions are for that location and time of year. For example, a D4 (Exceptional) drought may occur only a few times per century wcnc.com+1.
Expert Judgment and Field Input
While the data are objective, the USDM authors—rotating between the National Drought Mitigation Center (NDMC), USDA, and NOAA—use their judgment to reconcile conflicting indicators and interpret conditions at a regional scale Drought.gov+1. They consult a network of over 450 experts on the ground, who provide photos, descriptions, and observations USDA Farm Service Agency.
Process Timeline
- Data collection: Begins at 8 a.m. ET Tuesday, using the latest available station, satellite, and model data National Centers for Environmental Information.
- Analysis: Experts review precipitation, temperature, soil moisture, water levels, and impacts.
- Classification: Each U.S. county is assigned a category based on the rarity of the current conditions.
- Map release: Final map and statistics are published on Thursday Drought.gov+1.
Why Weekly Updates Matter
Because droughts develop and resolve gradually, the USDM is updated weekly to reflect short- and long-term trends. A single rain event may not clear a long-term drought, and prolonged dryness can worsen conditions over time wcnc.com.
In short, the USDM combines objective climate and hydrological data with expert interpretation and local knowledge to produce a timely, regionally relevant picture of drought conditions nationwide each week.