As the climate warms, the atmosphere is getting thirstier. Scientists define this atmospheric thirst, or evaporative demand, as the amount of water that could potentially evaporate from Earth’s surface in response to weather.
Standardized short-crop evapotranspiration (ETos) is a metric that estimates how much water would evaporate and transpire across a uniform, well-watered grass surface. It is used to measure the evaporative demand experienced by land covered by agricultural crops. Past studies have shown that ETos has increased over time in response to factors such as air temperature, solar radiation, humidity, and wind speed. But that research doesn’t cover patterns and trends over prolonged periods with exceptionally high atmospheric thirst.
Kukal and Hobbins designate a new term for these extreme ETos events: thirstwaves. A thirstwave is a period of extremely high evaporative demand that like its cousin the heat wave, can wreak havoc on a growing season. To be called a thirstwave, the ETos must be above the 90th percentile for at least 3 days.
The researchers studied ETos measurements for the contiguous United States for the 1981–2021 growing seasons, examining the intensity, duration, and frequencies of the thirstwaves they identified at the county level. They then grouped the results into nine regions.
The researchers’ analysis showed that thirstwaves occurred an average of 2.9 times throughout the growing season of April through October and had an average duration of 4 days. The longest duration was 17 days, and the greatest frequency was 20 events per season. Across the nation, the High Plains experienced the most intense thirstwaves; the South, Upper Midwest, Pacific Northwest, and West Coast experienced the longest average duration (approximately 4.5 days), and the West Coast and South experienced the highest frequency (around 3.5 events per season).
Thirstwaves have become more widespread and are affecting regions such as the Southwest, Northern Plains, and Northern Rockies, which might not have experienced them in previous decades. The likelihood that a region won’t experience a thirstwave at all during the year has also decreased. Continuing to measure and track thirstwaves will be crucial for crop and water management in the coming years, especially as the climate continues to warm, the researchers say. (Earth’s Future, https://doi.org/10.1029/2024EF004870, 2025)
This article originally appeared in EOS Magazine.
