Agriculture is the economic engine that powers the Great Plains, the vast stretch of treeless prairie that covers parts of 10 states – and where the next drought can appear with little warning. Now there's a powerful new tool that can provide farmers and ranchers in this arid region critical, early indications of oncoming droughts.

EDDI, or the Evaporative Demand Drought Index, was the brainchild of Mike Hobbins, a CIRES scientist working at NOAA, to estimate the changing “thirst” of the atmosphere.

“Evaporative demand is the thirst of the atmosphere for any water — on the surface of lakes and rivers, in soil or in plants,” he said. “Drought is a function of supply and demand. "Surface moisture is really hard to measure because a major component is soil moisture, which varies dramatically over very short distances, " explained Hobbins. "Evaporative demand is relatively easy to measure because it’s based on air temperature, humidity, wind speed, and solar radiation, which we measure all the time."

EDDI already has a good track record: The tool accurately signaled the onset of a 2015 Wyoming drought as well as 2016 droughts in South Dakota’s Black Hills and the southeastern United States. EDDI is valuable because it detects drought emergence at weekly time scales, said Mark Svoboda, co-founder of the U.S. Drought Monitor. “This year, it gave us a pretty good indicator of what was happening in the Dakotas,” as a crippling flash drought gripped the region, he said.

The U.S Famine Early Warning System network, which helps governments and relief agencies plan for and respond to humanitarian crises, has also begun using EDDI to help provide early warning of food insecurity (i.e., limited access to sufficient food supply) around the world.  

A case study over parts of East Africa shows that a combination of forecasts for both evaporative demand — atmospheric “thirst” — and precipitation would have provided early warning of severe droughts in 2002, 2004 and 2009 that contributed to substantial food shortages in the region.

“All else being equal, a warmer atmosphere is a thirstier atmosphere,” said Hobbins. “It’s likely we’ll see more frequent droughts in the future, and EDDI is uniquely designed to capture their emergence.”



The development and evaluation of EDDI is supported in part by the North Central Climate Science Center, through two projects led by Imtiaz Rangwala:

Developing Climate Change Understanding and Resources for Adaptation in the North Central U.S.

Ecological Drought, Climate Extremes, and the Water Cycle in the North Central U.S