U of I researcher coins āthirstwavesā as new framework emphasizing prolonged, extreme water stressors
March 20, 2025
Researchers from ¹ū¶³“«Ć½Ā鶹Éē (UĀ ofĀ I) and University of Colorado Boulder (CU Boulder) have created a new metric to help farmers, researchers and practitioners better track and prepare for prolonged periods of extremely high evaporative demand.
Meetpal Kukal, an assistant professor of hydrologic science and water management with UĀ ofĀ I, and Mike Hobbins, a senior research scientist with CU Boulder, have coined āthirstwavesā as a broad concept explaining when evaporative demand remains elevated for days at a time. Evaporative demand describes conditions governing the movement of water from the Earthās surface into the atmosphere.
Their paper āThirstwaves: Prolonged Periods of Agricultural Exposure to Extreme Atmospheric Evaporative Demand for Waterā was published March 20 in the journal ā.ā
In certain regions and seasons, windspeed, humidity or solar radiation from sunshine, rather than heat, drive evaporative demand. Evaporative demand drives evapotranspiration, as long as sufficient soil water is available.
āIn this whole domain of environmental change and its impacts, weāve been sort of obsessed about heat and heatwaves,ā explained Kukal, who is the paperās lead author. āAs far as water consumption by vegetation is concerned, including agricultural crops, there are other variables besides temperature that are equally, if not more, important, and that includes humidity, wind speed and solar radiation.ā
Their study evaluated the gridMET surface meteorological dataset covering the contiguous U.S. states from 1981 through 2021 growing seasons. They defined a thirstwave as having occurred any time when during at least three consecutive days daily evaporative demand was greater than its 90th percentile recorded historically.
Agricultural water managers traditionally consider mean values in their assessments. Thirstwaves, by contrast, focus on extremes persisting over multiple days.
āIf one were to look only at means it appears the southwest desert is the most extreme from a thirst standpoint. However, when you start looking at extremes, places that do not necessarily have high evaporative demand stand out as outliers,ā Kukal said. āThe Midwest, for example, is not as consequential from a mean evaporative demand standpoint, but from an extreme standpoint it is really a hot spot.ā Kukal published this evidence last year in the journal ā.ā
During prolonged durations of extreme stress from high heat, low humidity, high wind or high solar radiation, irrigation deliveries and equipment may not be able to put out water fast enough to keep up with demand.
Kukal is currently developing a decision-support dashboard to help southern Idaho farmers manage irrigation, factoring in the possibility of such extreme conditions and design limitations of irrigation systems. He and Hobbins looked at three unique aspects of thirstwaves from historical records: intensity, the number of events and the duration. They concluded all three aspects have been worsening over time, with thirstwaves becoming more intense, greater in number and more frequent.
āThese findings make us think about how our current water resources infrastructure, irrigation equipment and water management should mitigate and adapt,ā Kukal said. āAs these pressures grow, thereās less and less room for guesswork in irrigation, so if you are under limited water conditions, youāve got to do a better job at really tracking your water.ā
The researchers are optimistic that the concept of thirstwaves will add an important new framework to help agriculture bring the picture of evapotranspiration monitoring and forecasting for maintaining economic productivity into sharper focus. Kukalās research program at UĀ ofĀ I is building on Idahoās capacity to monitor and predict evapotranspiration to aid in decision-making.
āThis idea of thirstwaves I think is really going to catch on,ā Hobbins said. āItās a very powerful metric and itās 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.ā
About the ¹ū¶³“«Ć½Ā鶹Éē
The ¹ū¶³“«Ć½Ā鶹Éē, home of the Vandals, is Idahoās land-grant, national research university. From its residential campus in Moscow, U of I serves the state of Idaho through educational centers in Boise, Coeur dāAlene and Idaho Falls, nine research and Extension centers, plus Extension offices in 42 counties. Home to more than 12,000 students statewide, U of I is a leader in student-centered learning and excels at interdisciplinary research, service to businesses and communities, and in advancing diversity, citizenship and global outreach. U of I competes in the Big Sky and Western Athletic conferences. Learn more at uidaho.edu.