Click the link to read the research article on the AGU website (M. S. Kukal, M. Hobbins):
Abstract
Global atmospheric evaporative demand has increased, impacting agricultural productivity and water use. Traditionally, trend assessments have been limited to total evaporative demand, overlooking shifts in daily extremes, which are meaningful for agrohydrological outcomes yet largely unknown. Here, using a fully physical metric of evaporative demand, that is, standardized short crop reference evapotranspiration, we introduce the concept of thirstwaves—prolonged periods of extremely high evaporative demand—and analyze their characteristics during 1981–2021 growing seasons for the conterminous US. Findings show that long-term mean spatial patterns demonstrated by thirstwave characteristics do not follow that of total or mean evaporative demand. Weighted for cropland area harvested, thirstwave intensity, duration, and frequency have increased by 0.06 mm d−1 decade−1, 0.10 days decade−1, and 0.39 events decade−1, respectively during 1981–2021. Statistically significant trends appear across 17%, 7%, and 23% of cropland area for intensity, frequency, and duration. Not only have thirstwaves increased in severity, but the likelihood of no thirstwaves occurring during the growing season has significantly decreased. Our work proposes a novel metric to describe periods of extremely elevated evaporative demand and presents a systematic analysis of such conditions historically for US croplands.
Key Points
- Regional hotspots of thirstwaves do not necessarily align with areas of high overall evaporative demand
- Intensity, duration, and frequency of thirstwaves have increased significantly (p < 0.05) over 17%, 7%, and 23% of US cropland area, respectively
- The likelihood of no thirstwaves occurring during the growing season has significantly decreased
Plain Language Summary
The atmosphere is getting more demanding for water around the world, and this affects water use and farming outcomes. Previously, studies mainly looked at the overall atmospheric demand for water, but little is known about changes in occurrence of very high atmospheric demand for water over consecutive days. In this study, we use introduce the idea of “thirstwaves,” which are long periods of very high atmospheric demand for water. We looked at these thirstwaves that have occurred during 1981–2021 in the US and analyzed them for how intense and how frequent they were and how many days they lasted. We found that the worst thirstwaves happened in places that do not see the highest demand. Over time, all aspects of these thirstwaves have gotten worse. It has also become much less likely that a growing season will pass without any thirstwaves. These findings suggest that in addition to monitoring overall atmospheric demand for water, it’s important to track, measure, and report thirstwaves to those managing agriculture and water resources.