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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 examines how anomalous the atmospheric evaporative demand (E0; also known as "the thirst of the atmosphere") is for a given location and across a time period of interest. EDDI maps use atmospheric evaporative demand anomalies across a timescale of interest relative to its climatology to indicate the spatial extent and severity of drought. EDDI 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).

Interactive Map: Evaporative Demand Drought Index (EDDI)

EDDI data from NOAA's Physical Sciences Laboratory (PSL) were available in ACSII format. The ASCII data was ingested and converted raster data using GIS. EDDI data is updated daily. 

GIS Data

EDDI data from NOAA's Physical Sciences Laboratory (PSL) were available in ACSII format. The ASCII data was ingested and converted raster data using GIS. EDDI data is updated daily. 

GIS Data

Drought Categories
Value Map Hex Color
ED4 #730000
ED3 #e60000
ED2 #ffaa00
ED1 #ffd37f
ED0 #ffff00
Wetness Categories
Value Map Hex Color
EW0 #8ccdef
EW1 #00bfff
EW2 #1d90ff
EW3 #4169e1
EW4 #0000ff
Drought Categories
Value Map Hex Color
ED4 #730000
ED3 #e60000
ED2 #ffaa00
ED1 #ffd37f
ED0 #ffff00
Wetness Categories
Value Map Hex Color
EW0 #8ccdef
EW1 #00bfff
EW2 #1d90ff
EW3 #4169e1
EW4 #0000ff

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”

Access

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)

Documention

Description

The Evaporative Demand Drought Index (EDDI) uses atmospheric evaporative demand (E0) anomalies across a timescale of interest relative to its climatology to indicate the spatial extent and severity of drought. The E0 is calculated using the Penman-Monteith FAO56 reference evapotranspiration formulation (0.5-m tall reference crop), driven by data on temperature, humidity, wind speed, and incoming solar radiation, with these data extracted from the operational 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 same accumulation time-window in the whole period of record (1979-present), using a rank-based non-parametric method described in Hobbins et al. (2016; see the "Resources" tab). EDDI data are available at a ~12-km resolution (0.125° lat and long) across CONUS since January 1, 1980, and are updated daily.

On the EDDI Category Maps, colors indicate the frequency at which the observed E0 anomaly has occurred in the climatology, with warm colors indicating conditions that are drier than normal and cool colors indicating wetter-than-normal conditions. As an example, the ED4 category indicates that the current E0 anomaly has only been observed less than 2% of the time in the past 38 years (1979-2016), which represents the most severe drought conditions; the EW4 category means indicates that the anomaly has been exceeded 98% of the time, which represents the wettest conditions. For plotting purposes, EDDI values are binned into different percentile categories analogous to the U.S. Drought Monitor plots—however, in case of EDDI plots, both drought and anomalously wet categories are shown.

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.

Related Web Pages

References

  • 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.

Acknowledgements

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