Most people have heard of heatwaves: extended periods of abnormally hot weather. But researchers from CIRES and the University of Idaho have coined a new term to describe extended periods of atmospheric thirst. Studying these ‘thirstwaves’ can help farmers better manage their water resources and improve crop yields, according to the researchers. 

Evaporative demand refers to how ‘thirsty’ Earth’s atmosphere is, or how readily it sucks up moisture from plants, soil, and bodies of water. A combination of factors drives evaporative demand, including temperature, wind speed, humidity, and sunshine. 

Mike Hobbins, a CIRES researcher in NOAA’s Physical Sciences Laboratory, and Meetpal Kukal, a research hydrologist at the University of Idaho, define thirstwaves as periods where evaporative demand is elevated for extended periods. They describe the new term and examine past United States thirstwaves in a new paper published today in Earth’s Future. 

“This idea of thirstwaves I think is really going to catch on,” Hobbins said. “It’s a very powerful metric and it’s a crucial distinction from heatwaves, because we have been hobbled for decades by this idea that temperature is really the only place where the information is.” 

Hobbins and Kukal define a thirstwave as at least three consecutive days when daily evaporative demand was greater than its historical 90^th percentile value for that period. In the new study, they analyzed thirstwaves in the contiguous United States from 1980 to 2021. They found thirstwaves have become 17 percent more intense and 23 percent more frequent over the past four decades. They also found thirstwaves are lasting longer than in the past and are now much more likely to occur during the growing season. 

“These findings make us think about how our current water resources infrastructure, irrigation equipment, and water management should mitigate and adapt,” Kukal said. “As these pressures grow, there’s less and less room for guesswork in irrigation, so if you are under limited water conditions, you’ve got to do a better job at really tracking your water.”

Farmers have traditionally considered average evaporative demand values for their region when determining how much water their crops will need. But the new results show thirstwaves occur more often in areas with lower average evaporative demand, like the Midwest, than in traditionally dry areas, like the Southwest desert. 

More thirstwaves means crops will need more water, and irrigation deliveries and equipment may not be able to put out water fast enough to keep up with demand, according to the researchers. Kukal is currently developing a decision-support dashboard to help southern Idaho farmers better manage irrigation, factoring in the possibility of thirstwaves and current design limitations of irrigation systems.