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Abstract Human heat stress depends jointly on atmospheric temperature and humidity. Wetter soils reduce temperature but also raise humidity, making the collective impact on heat stress unclear. To better understand these interactions, we use ERA5 to examine the coupling between daily average soil moisture and wet-bulb temperature (Tw) and its seasonal and diurnal cycle at global scale. We identify a global soil moisture–Twcoupling pattern with both widespread negative and positive correlations in contrast to the well-established cooling effect of wet soil on dry-bulb temperature. Regions showing positive correlations closely resemble previously identified land–atmosphere coupling hotspots where soil moisture effectively controls surface energy partition. Soil moisture–Twcoupling varies seasonally closely tied to monsoon development, and the positive coupling is slightly stronger and more widespread during nighttime. Local-scale analysis demonstrates a nonlinear structure of soil moisture–Twcoupling with stronger coupling under relatively dry soils. Hot days with highTwvalues show wetter-than-normal soil, anomalous high latent and low sensible heat flux from a cooler surface, and a shallower boundary layer. This supports the hypothesis that wetter soil increasesTwby concentrating surface moist enthalpy flux within a shallower boundary layer and reducing free-troposphere-air entrainment. We identify areas of particular interest for future studies on the physical mechanisms of soil moisture–heat stress coupling. Our findings suggest that increasing soil moisture might amplify heat stress over large portions of the world including several densely populated areas. These results also raise questions about the effectiveness of evaporative cooling strategies in ameliorating urban heat stress. Significance StatementThe purpose of this study is to provide a global picture of the relationship between soil moisture anomalies and a heat stress metric that includes the joint effects of temperature and humidity. This is important because a better understanding of this relationship will help improve the prediction of extreme heat stress events and inform strategies for ameliorating heat stress. We find a widespread positive correlation between soil moisture and heat stress, in contrast to studies relying on temperature alone. This raises the possibility that, over much of the world, and in the most populous regions, strategies like irrigation or “greening” that can reduce temperature might be ineffective or even harmful in reducing heat stress with humidity incorporated.
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Recent shift from energy- to moisture-limitation over global croplands
Abstract Hot and dry conditions pose a substantial risk to global crops. The frequency of co-occurring heat and drought depends on land–atmosphere coupling, which can be quantified by the correlation between temperature and evapotranspiration (r(T, ET)). We find that the majority of global croplands have experienced declines inr(T, ET) over the past ∼40 years, indicating a shift to a more moisture-limited state. In some regions, especially Europe, the sign ofr(T, ET) has flipped from positive to negative, indicating a transition from energy-limitation to moisture-limitation and suggesting a qualitative shift in the local climate regime. We associate stronger declines inr(T, ET) with faster increases in annual maximum temperatures and larger declines in soil moisture and ET during hot days. Our results suggest that shifts towards stronger land–atmosphere coupling have already increased the sensitivity of crop yields to temperature in much of the world by 12%–37%, as hot days are not only hotter, but also more likely to be concurrently dry.
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- PAR ID:
- 10521551
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 19
- Issue:
- 6
- ISSN:
- 1748-9326
- Page Range / eLocation ID:
- 064065
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1748-9326/ad5032
