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Abstract Irrigation plays a crucial role in agricultural production across the US Great Plains. Meanwhile, it is a key driver of local and regional climate due to its influence on energy and water exchange between land surface and atmosphere. Despite the irrigation-induced evaporative cooling on temperature alone, how irrigation affects summer heat stress—a combination of temperature and humidity can become a concern to public health—is not well understood. This study examines the potential impacts of irrigation practices on summer temperature and heat extremes in the Great Plains using a set of sensitivity experiments conducted with the Weather Research & Forecasting (WRF) model for 10 growing seasons. Results show that intensive irrigation lowers the ambient temperature, but the increased humidity from enhanced evapotranspiration, especially during the extreme hot and dry summers, can possibly elevate the risks of heat stress in the heavily irrigated area and its surroundings. The response of humid heat extremes to irrigation depends on the heat metrics used in the assessment. For variables like wet-bulb temperature, wet-bulb globe temperature, and equivalent temperature, irrigation leads to significantly intensified humid heat extremes by up to 5 °C and increased heatwave frequency by 3 events year−1. In contrast, metrics like the heat index and environmental stress index suggest that irrigation mitigates heat intensity by decreasing the temperature metrics by up to 1 °C. Given the importance of irrigation in Great Plains agriculture in a changing climate, these uncertainties underscore the urgent need to connect heat metrics with health outcomes to better address heat mitigation in rural communities.
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Stickiness: A New Variable to Characterize the Temperature and Humidity Contributions toward Humid Heat
Abstract Extreme wet-bulb temperatures (Tw) are often used as indicators of heat stress. However, humid heat extremes are fundamentally compound events, and a givenTwcan be generated by various combinations of temperature and humidity. Differentiating between extreme humid heat driven by temperature versus humidity is essential to identifying these extremes’ physical drivers and preparing for their distinct impacts. Here we explore the variety of combinations of temperature and humidity contributing to humid heat experienced across the globe. In addition to using traditional metrics, we derive a novel thermodynamic state variable named “stickiness.” Analogous to the oceanographic variable “spice” (which quantifies the relative contributions of temperature and salinity to a given water density), stickiness quantifies the relative contributions of temperature and specific humidity to a givenTw. Consistent across metrics, we find that high magnitudes ofTwtend to occur in the presence of anomalously high moisture, with temperature anomalies of secondary importance. This widespread humidity dependence is consistent with the nonlinear relationship between temperature and specific humidity as prescribed by the Clausius–Clapeyron relationship. Nonetheless, there is a range of stickiness observed at moderate-to-highTwthresholds. Stickiness allows a more objective evaluation of spatial and temporal variability in the temperature versus humidity dependence of humid heat than traditional variables. In regions with high temporal variability in stickiness, predictive skill for humid heat-related impacts may improve by considering fluctuations in atmospheric humidity in addition to dry-bulb temperature. Significance StatementExtreme humid heat increases the risk of heat stress through its influence over humans’ ability to cool down by sweating. Understanding whether humid heat extremes are generated more due to elevated temperature or humidity is important for identifying factors that may increase local risk, preparing for associated impacts, and developing targeted adaptation measures. Here we explore combinations of temperature and humidity across the globe using traditional metrics and by deriving a new variable called “stickiness.” We find that extreme humid heat at dangerous thresholds occurs primarily due to elevated humidity, but that stickiness allows for thorough analysis of the drivers of humid heat at lower thresholds, including identification of regions prone to low- or high-stickiness extremes.
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- Award ID(s):
- 1933523
- PAR ID:
- 10581486
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 81
- Issue:
- 5
- ISSN:
- 0022-4928
- Page Range / eLocation ID:
- 819 to 837
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1175/JAS-D-23-0072.1
