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Evaporative Demand Drought Index (EDDI)

Associated Agencies

National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratories (ESRL) Physical Sciences Laboratory (PSL)

The Evaporative Demand Drought Index (EDDI) is an experimental tool that 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).

How to

What can I do with these data?

EDDI has been shown to offer early warning of drought stress relative to current operational drought indicators, such as the US Drought Monitor (USDM). A particular strength of EDDI is in capturing the precursor signals of water stress at weekly to monthly timescales, which makes EDDI a potent tool for drought preparedness at those timescales. EDDI also uses the same classification scheme as the USDM to define drought conditions, so it is easy to read EDDI maps.

How do I use the EDDI site?

  • Select the “Current Conditions” section of the EDDI web page.
  • Select the time unit (weeks or months) and time window of choice (1-12) and press “Plot Map”


Currently, EDDI is generated daily – though with a 5-day lag-time – by analyzing a near-real-time atmospheric dataset. There is also an ongoing effort to forecast EDDI based on seasonal climate-forecast information.

Maps and Time Series Visualization – Real-time maps and time-series analysis from NOAA’s Earth Systems Research Lab (ESRL)



EDDI is a drought indicator that uses atmospheric evaporative demand (E0) anomalies across a time-window of interest relative to its climatology to indicate the spatial extent and severity of drought. This page provides access to near-real-time (with a five-day latency, i.e., the most recent information is five days old) EDDI plots with time windows integrating E0 anomalies from 1 to 12 weeks and 1 to 12 months from the most current date. E0 is calculated using the Penman Monteith FAO56 reference evapotranspiration formulation driven by temperature, humidity, wind speed, and incoming solar radiation from the North American Land Data Assimilation System (NLDAS-2) dataset. For a particular time-window, EDDI is estimated by standardizing the E0 anomalies relative to the whole period of the record (1979-present), using a non-parametric method (see Hobbins et al., 2016). For plotting purposes, EDDI values are binned into different percentile categories analogous to the US Drought Monitor plots. However, in case of EDDI plots, both drought and anomalously wet categories are shown. EDDI data are available at a ~12-km resolution across CONUS since January 1, 1980, and are updated daily.

EDDI has the potential to offer early warning of agricultural drought, hydrologic drought, and fire-weather risk by providing real-time information on the emergence or persistence of anomalous evaporative demand in a region. A particular strength of EDDI is in capturing the precursor signals of water stress at weekly to monthly timescales, which makes EDDI a strong tool for drought preparedness at those timescales.

For more information regarding these plots, please contact Mike Hobbins: (; 303-497-3092).

Related Web Pages


  • Michael Hobbins, Andrew Wood, Daniel McEvoy, Justin Huntington, Charles Morton, James Verdin, Martha Anderson, and Christopher Hain (June 2016): The Evaporative Demand Drought index: Part I – Linking Drought Evolution to Variations in Evaporative Demand. J. Hydrometeor., 17(6),1745-1761. doi:10.1175/JHM-D-15-0121.1.
  • Daniel J. McEvoy, Justin L. Huntington, Michael T. Hobbins, Andrew Wood, Charles Morton, James Verdin, Martha Anderson, and Christopher Hain (June 2016) The Evaporative Demand Drought index: Part II – CONUS-wide Assessment Against Common Drought Indicators. J. Hydrometeor., 17(6), 1763-1779. doi:10.1175/JHM-D-15-0121.1.


This work is supported in part by grants from (i) NOAA’s Research Transition Acceleration Program (RTAP) for the project titled “Operationalizing an Evaporative Demand Drought Index (EDDI) service for drought monitoring and early warning;” (ii) NOAA’s Sectoral Applications Research Program (SARP): Coping with Drought in Support of the National Integrated Drought Information System (NIDIS) program for the project titled “Developing a wildfire component for the NIDIS California Drought Early Warning System;” and (iii) DOI's North Central Climate Science Center for the project titled "Evaporation, Drought, and the Water Cycle across Timescales.”

Representative Image
Example images of the EDDI product