The Evaporative Demand Drought Index (EDDI) is an experimental drought monitoring tool that measures how anomalous the atmospheric evaporative demand (E₀) (also known as "the thirst of the atmosphere") is for a given location across a timescale of interest. EDDI uses evaporative demand anomalies relative to climatology to indicate the spatial extent and severity of drought.
A particular strength of EDDI is its ability to capture precursor signals of water stress at weekly to monthly timescales. It can serve as an indicator of both rapidly evolving "flash" droughts (developing over a few weeks) and sustained droughts (developing over months but lasting up to years), offering early warning of agricultural drought, hydrologic drought, and fire-weather risk, even when precipitation has been near-normal.
Inputs: Temperature, humidity, wind speed, and incoming solar radiation, extracted from the North American Land Data Assimilation System phase 2 (NLDAS-2) dataset. E₀ is calculated using the Penman-Monteith FAO56 reference evapotranspiration formulation. Data are available at ~12 km resolution across the contiguous U.S. since January 1, 1980, and are updated daily with a 5-day lag.
How to interpret EDDI values:
|
Category |
Classification |
Meaning |
|---|---|---|
|
ED4 |
Exceptional Drought |
Evaporative demand exceeds 98–100% of historical values |
|
ED3 |
Extreme Drought |
Evaporative demand exceeds 95–98% of historical values |
|
ED2 |
Severe Drought |
Evaporative demand exceeds 90–95% of historical values |
|
ED1 |
Moderate Drought |
Evaporative demand exceeds 80–90% of historical values |
|
ED0 |
Abnormally Dry |
Evaporative demand exceeds 70–80% of historical values |
|
EW0 |
Abnormally Wet |
Evaporative demand in the bottom 20–30% of historical values |
|
EW1 |
Moderate Wet |
Evaporative demand in the bottom 10–20% of historical values |
|
EW2 |
Severe Wet |
Evaporative demand in the bottom 5–10% of historical values |
|
EW3 |
Extreme Wet |
Evaporative demand in the bottom 2–5% of historical values |
|
EW4 |
Exceptional Wet |
Evaporative demand in the bottom 0–2% of historical values |
Source: NOAA's Climate Prediction Center Evaporative Demand Drought Index (EDDI), which provides near-real-time EDDI maps, change maps, attribution maps, and time series data for the contiguous U.S.