Land–atmosphere coupling influences both heatwaves and droughts, but evidence from climate science indicates it tends to be more influential during heatwaves because soil moisture directly modulates surface energy partitioning and atmospheric heating. Research led by Sonia Seneviratne at ETH Zurich highlights how reduced soil moisture limits evaporative cooling, increasing sensible heat flux and surface temperature. Johannes Schär at ETH Zurich has shown similar feedbacks in European heat events, where dry soils amplified extreme daytime temperatures. These mechanisms make heatwaves particularly sensitive to local land conditions.
Mechanisms
At the core is the role of soil moisture in controlling the partitioning of net radiation into latent and sensible heat. When soils are moist, more incoming energy goes into evaporation, which cools the surface. When soils are dry, evaporation is suppressed and energy heats the air instead. This soil moisture feedback accelerates warming during heatwaves, creating a positive loop: higher temperatures dry soils further, which then allows temperatures to rise even more. This feedback is strongest in transitional climates—regions that alternate between wet and dry seasons—because they sit near the threshold where evapotranspiration becomes soil-limited.
Implications
For droughts, land–atmosphere coupling plays an important but somewhat different role. Coupling can influence drought persistence and severity by reducing local moisture recycling and suppressing afternoon precipitation, but the primary drivers of drought onset are often large-scale circulation patterns and deficits in precipitation that originate remotely. Consequently, while coupling can exacerbate a drought once it begins, it is generally less decisive in initiating droughts than it is in intensifying heatwaves.
Human and territorial factors modify these physical processes. Irrigation, land-use change, and urbanization alter local soil moisture and surface properties, weakening or redirecting coupling; for example, irrigated agriculture can mitigate heat extremes locally, while deforestation or urban heat islands can intensify them. Culturally and economically, regions dependent on agriculture face compounded risks when heatwaves and drought interact, because heat amplified by soil–atmosphere feedbacks can quickly degrade crop yields and water resources.
Overall, expert analyses from researchers such as Sonia Seneviratne and Johannes Schär at ETH Zurich support the conclusion that land–atmosphere coupling is typically more influential during heatwaves, while still playing a consequential, but secondary, role in drought dynamics. Local land management thus matters for both adaptation and risk reduction.