Description of Maps and Underlying Data

The EDDI maps displayed here use atmospheric evaporative demand (E₀) anomalies across a timescale of interest relative to its climatology to indicate the spatial extent and severity of drought. This page provides access to historic and near-real-time (with a five-day latency, i.e., the most recent information is five days old) EDDI plots with timescales that measure E₀ anomalies across the 1 to 12 weeks and 1 to 12 months prior to the most current date. The 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 US Drought Monitor plots—however, in case of EDDI plots, both drought and anomalously wet categories are shown.

E₀ is calculated using the Penman Monteith FAO56 reference evapotranspiration formulation (0.5m tall reference crop), driven by temperature, humidity, wind speed, and incoming solar radiation 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 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). EDDI data are available at a ~12-km resolution (0.125° lat and long) across CONUS since January 1, 1980, and are updated daily.

Click here for access to these CONUSwide plots and here for access to the CONUSwide data. For more information regarding the plots and data, including arranging for customized EDDI maps, please contact yutong.pan@noaa.gov (Phone: 443-996-7263).