Soil heat extremes outpace their atmospheric counterpart

Abstract Hot temperature extremes are changing in intensity and frequency. Quantifying these changes is key for developing adaptation strategies [1]. The conventional approach to study changes in hot extremes is based on air temperatures. However, hydrology [2] and many biogeochemical processes, e.g. decomposition of organic material and release of CO2 [3]- are more sensitive to soil rather than air temperature. In this study, we show that soil hot extremes are increasing faster than air hot extremes by 0.7° C/Decade in intensity and twice as fast in frequency on average over Central Europe. Furthermore, we identify soil temperature as a factor in the soil moisture–temperature feedback. During dry conditions, increases in net radiation yield higher soil temperature and a consequent release of sensible heat while latent heat flux is constrained by soil moisture deficits. The release of sensible heat from soils leads to increases in air temperature and vapour pressure deficit that may further dry out and warm up the soil. This study further highlights the contribution of soil moisture–temperature feedback to the evolution of hot extremes in a warming climate. The rapid increase in soil heat extremes shown in these results may have important implications for climate and ecological risk applications.