Environmental Research Letters (Jan 2024)
The U.S. Midwest and High Plains Aquifer-fed croplands are previously unrealized hotspots of extreme evaporative demand exposure
Abstract
Total evaporative demand or atmospheric thirst is a primary determinant of agroecosystems’ water use and an indispensable input to scientifically based irrigation design and management. However, despite its extensive use to represent agricultural environments, it has not been assessed for its extreme behavior. Prolonged exposure to extreme evaporative demand conditions a.k.a thirstwaves can be especially stressful for agricultural output, water use, and management, but remain uninvestigated owing to lack of meaningful metrics for quantifying and reporting ‘extreme thirst exposure’. In this letter, I present spatial (county-level) and temporal (1981–2021) changes in exposure to extreme thirst during the agricultural growing season across the conterminous U.S. (CONUS). Using a fully physical metric of evaporative demand, i.e., standardized short crop reference evapotranspiration (ET _o ), I define two novel measures: cumulative extreme thirst exposure (thirst _cum ) and average extreme thirst anomaly (thirst _anom ) to represent the seasonal-level severity of thirstwaves. Both metrics showed significant spatiotemporal variation with long-term averages of 12 mm (thirst _cum ) and 0.66 mm d ^−1 (thirst _anom ) for CONUS. Distinct spatial patterns were revealed for extreme thirst exposure that had little in common with those observed for total ET _o . Spatially, hotspots of high extreme thirst exposure were co-located with the Midwest and High Plains aquifer regions, that account for 64% of total acreage and 28% of irrigated acreage nationally, respectively. Critical for food and water security, these regions have experienced the highest extreme thirst exposure nationally, hence necessitating reevaluation of regional disparities in water stress. While thirst _cum and thirst _anom have increased by 5.6 mm and 0.21 mm d ^−1 on an average in CONUS, worsening of extreme thirst exposure is especially concerning for the High Plains aquifer region (12.6 mm and 0.54 mm d ^−1 , respectively). The emergence of previously unrealized hotspots in regions critical for water security uncover potential pitfalls for planning and adaptation that may result from overlooking extreme measures of evaporative demand.
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