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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Hydrology and Remote Sensing Laboratory » Research » Publications at this Location » Publication #327050
Title: The evaporative demand drought index: Part I 1 – Linking drought evolution to variations in evaporative demand

Author
item HOBBINS, M. - University Of Colorado
item WOOD, A. - National Center For Atmospheric Research (NCAR)
item MCEVOY, D. - Desert Research Institute
item HUNTINGTON, J. - Desert Research Institute
item MORTON, C. - Desert Research Institute
item VERDIN, J. - Us Geological Survey (USGS)
item Anderson, Martha
item HAIN, C. - University Of Maryland

Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2016
Publication Date: 6/1/2016
Citation: Holmes, T., Hain, C., Anderson, M.C., Crow, W.T. 2016. Cloud tolerance of remote sensing technologies to measure land surface temperature hydrology and earth system sciences . Journal of Hydrometeorology. SCIENCES.

Interpretive Summary: Rapid onset, or "flash", drought events are caused by a combination of lower-than-average rainfall and hot, dry and windy conditions that accelerate evaporation of soil moisture into the atmosphere. The drying power of the atmosphere is called the evaporative demand, and it can be mapped using standard meteorological datasets describing air temperature, vapor pressure, wind speed and solar radiation. Early signals of potential for flash drought onset might be revealed in maps of evaporative demand, providing valuable early warning for farm management or famine relief decision making. This hypothesis was tested in this paper, investigating behavior of a new Evaporative Demand Drought Index (EDDI), describing anomalies in evaporative demand over the continental U.S. over the past decade. The EDDI was compared with several other drought indicators, including the U.S. Drought Monitor, and found to provide early precursor signals preceeding major flash drought events. The EDDI can be combined with indicators describing decrease in soil moisture and increase in crop stress, providing evidence that the atmospheric potential for drought had progressed to actual agricultural drought conditions on the ground. Together, these indices paint a more complete picture of how flash drought events evolve and what the expected impacts will be.

Technical Abstract: Many operational drought indices focus primarily on precipitation and temperature when depicting hydroclimatic anomalies, and this perspective can be augmented by analyses and products that reflect the evaporative dynamics of drought. We leverage the linkage between atmospheric evaporative demand (E0) and actual evapotranspiration (ET) in a new drought index based solely on E0—the Evaporative Demand Drought Index (EDDI). EDDI measures the signal of drought through the response of E0 to surface drying anomalies that result from two distinct land surface-atmosphere interactions: (1) a complementary relationship between E0 and ET that develops as moisture becomes limited at the land surface, leading to ET declining and increasing E0, as in sustained droughts; and (2) parallel ET and E0 increases arising from increased energy availability leading to surface moisture limitation, as in flash droughts. To calculate EDDI from E0, we use a long-term, daily reanalysis of reference ET estimated by the American Society of Civil Engineers (ASCE) Standardized Reference ET equation using radiation and meteorological variables from the North American Land Data Assimilation System (NLDAS) phase-2. EDDI is derived by deriving empirical probabilities of aggregated E0 depths relative to their climatologic means across a user38 specific time period and normalizing these probabilities. Positive EDDI values then indicate drier than normal conditions and the potential for drought. EDDI is a physically based, multi-scalar drought index that that can serve as an indicator of both flash and sustained droughts, in some hydroclimates offering early warning relative to current operational drought indices.