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  Please see this for an updated discussion of the impact of the input data having errors for a portion of the record.AboutAccess All Data &  Images **EDDI User Guide **What is EDDI?
**The Evaporative Demand Drought Index (EDDI)** is an experimental drought monitoring and early warning guidance tool. Itexamines how anomalous the atmospheric evaporative demand (E0; also known as "the thirst of theatmosphere") is for a given location and across a time period of interest. EDDI is multi-scalar,meaning that this period—or "timescale"—can vary to capture drying dynamics that themselvesoperate at different timescales; we generate EDDI at 1-week through 12-month timescales.

This webpage offers a frequently updated assessment of current conditionsacross CONUS, southern parts of Canada, and northern parts of Mexico; a tool to generate historical time seriesof EDDI for a user-selected region; introductions to the EDDI team; and a list of resources for users toexplore EDDI and its applications further.
Why use EDDI?
EDDI can offer early warning of agricultural drought, hydrologic drought, and fire-weather riskby providing near-real-time information on the emergence or persistence of anomalous evaporativedemand in a region. A particular strength of EDDI is in capturing the precursor signals of waterstress at weekly to monthly timescales, which makes EDDI a strong tool for preparedness for bothflash droughts and ongoing droughts.
How often is EDDI updated?
Currently, EDDI is generated daily—though with a 5-day lag-time—by analyzing a near-real-timeatmospheric dataset. This lag-time results from the procedures to quality control themeteorological data used to estimate evaporative demand. There is also an ongoing effort toforecast EDDI based on seasonal climate-forecast information.
Acknowledgements
This work is supported in part by grants from (i) NOAA's Joint Technology Transfer Initiative(JTTI) for the project titled "Operationalizing an Evaporative Demand Drought Index (EDDI)service for drought monitoring and early warning;" (ii) NOAA's Sectoral Applications ResearchProgram (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 NIDISCalifornia Drought Early Warning System;" (iii) DOI's North Central Climate Science Center forthe project (Grant #G14AP00182) titled "Ecological Drought, Climate Extremes and the Water Cycle across Timescales;"and (iv) Western Water Assessment, an NOAA RISA program, for the project titled "Enhancing theusability of EDDI," with funding originating from NIDIS.

Any issues with accessing the plots and other information on this page are welcome and should besent to psl.data@noaa.gov.
    Please read this for an issue with potentially incorrect input data to EDDI causing excessive dry conditions being indicated over the NE and N Central USCurrent EDDI Maps and EDDI-change Maps for the Contiguous U.S.20240919 Week Month 01 02 03 04 05 06 07 08 09 10 11 12EDDI Category MapASCII Data for This PlotAll Data & Images EDDI Change MapsIf you use these plots in publications, we ask that you acknowledge the Physical Sciences Laboratory. For example: "Image provided by the NOAA/ESRL Physical Sciences Laboratory, Boulder, Colorado, from their web site at: https://psl.noaa.gov/eddi/."Description of Maps and Underlying Data
The EDDI maps displayed here use atmospheric evaporative demand (E0) anomalies across atimescale of interest relative to its climatology to indicate the spatial extent and severity ofdrought. This page provides access to near-real-time maps (with a five-day latency due to themost recent information being five days old) depicting both EDDI (EDDI Category Maps) andchanges in EDDI (EDDI Change Maps), with timescales that measure E0 anomalies across the 1 to 12weeks and 1 to 12 months prior to the most current date.

The E0 is calculated using the Penman-Monteith FAO56 reference evapotranspirationformulation (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 LandData 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-basednon-parametric method described in Hobbins et al. (2016; see the "Resources" tab). EDDI data areavailable 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 hasoccurred in the climatology, with warm colors indicating conditions that are drier than normaland cool colors indicating wetter-than-normal conditions. As an example, the ED4 categoryindicates that the current E0 anomaly has only been observed less than 2% of the time in thepast 38 years (1979-2016), which represents the most severe drought conditions; the EW4 categorymeans indicates that the anomaly has been exceeded 98% of the time, which represents the wettestconditions. For plotting purposes, EDDI values are binned into different percentile categoriesanalogous to the US Drought Monitor plots—however, in case of EDDI plots, both drought andanomalously wet categories are shown.

On the **EDDI Change Maps**, the evolution in EDDI is depicted over the period indicated in thetitle. For instance, the "1-month EDDI: Changes during the 7 days ending on March 10, 2021"shows by how many categories 1-month EDDI has changed from March 3 to March 10. Brown colorsindicate deepening drought conditions (say from D0 to D1, which would show as a category changeof -1); green colors indicate ameliorating drought conditions (say from D2 to D1, which wouldshow as a category change of 1). In each case, deeper shades indicate greater changes in EDDIacross the period. Only a few change periods are shown for each EDDI category map. Note these maps onlydepict regions either starting or ending the change period in categories D0-D4; regions that areeither not in drought during the change period or that leave drought during the change periodare shown as blank.

For more information regarding these plots and access to data, including customized EDDI maps, please contactMike.Hobbins@noaa.gov (Phone: 307-228-0815)
** EDDI User Guide(pdf)** How to read an EDDI map(pdf)This is a Research and Development Application