Soil heat extremes can outpace air temperature extremes

Quantifying changes in hot temperature extremes is key for developing adaptation strategies. Changes in hot extremes are often determined on the basis of air temperatures; however, hydrology and many biogeochemical processes are more sensitive to soil temperature. Here we show that soil hot extremes are increasing faster than air hot extremes by 0.7 °C per decade in intensity and twice as fast in frequency on average over Central Europe. Furthermore, we identify soil temperature as a key factor in the soil moisture–temperature feedback. During dry and warm conditions, the energy absorbed by the soil is used to warm the soil, increasing the release of sensible heat flux and surface air temperatures. This increase in surface air temperature leads to a higher atmospheric demand for water, increasing soil evaporation, which may further dry and warm the soil highlighting the contribution of soil moisture–temperature feedback to the evolution of hot extremes in a warming climate. Changes in air temperature are usually considered for quantifying changes in temperature extremes such as heatwaves. This study shows that the incidence of heat extremes in soils is increasing faster than air temperature in some regions, with implications for hydrological and biogeochemical processes.