New NOAA Drought Index: Evaporative Demand Drought Index

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The Evaporative Demand Drought Index (EDDI) examines how anomalous the atmospheric evaporation demand is for a given location and across a time period of interest according to NOAA. Atmospheric evaporation demand is often referred to as “the thirst of the atmosphere”. The timescale of this index can vary to capture drying dynamics that themselves operate at different timescales.

Fig. 1: The Evaporative Demand Drought Index (EDDI) for April 14, 2021.

Fig. 2: The Evaporative Demand Drought Index (EDDI) for April 14, 2021.

What is EDDI? The Evaporative Demand Drought Index (EDDI) examines how anomalous the atmospheric evaporation demand is for a given location and across a time period of interest according to NOAA. Atmospheric evaporation demand is often referred to as “the thirst of the atmosphere”. The timescale of this index can vary to capture drying dynamics that themselves operate at different timescales.

EDDI can offer early warning of agriculture drought, hydrologic drought, and fire-risk by providing near real-time information on the emergence or persistence of anomalous evaporative demand in a region according to NOAA. NOAA indicates EDDI’s main purpose to identify the potential for flash drought potential.

NOAA states that EDDI is issued daily and based on a 5-day lag. The most recent analysis dated April 14 is indicated in Fig. 1. The EDDI web site is below.

Evaporative Demand Drought Index (EDDI): NOAA Physical Sciences Laboratory

Most recent EDDI discussion (by Climate Impact Company): The April 14, 2021 analysis is based on a 12-week time scale. The analysis reveals ED4 conditions which represent optimum flash drought risk is present in the eastern Great Lakes/northeast Ohio Valley region, the Southwest U.S. to California, the northern Great Plains and far southern Florida. The analysis is very specific about the most rigorous drought risk areas. Wet zones are present mostly across the Northwest U.S. and Louisiana. The 90-day EDDI change analysis (Fig. 2) indicates the driest trend is across the Southwest, North-central and Northeast U.S.

Summary: The EDDI appears to be a definite upgrade in soil moisture analysis. Data appears to be routinely available. A lengthy historical data base is also available on the web site indicated above. Climate Impact Company will now issue frequent analysis/statements based on EDDI analysis going forward.