2025/11/11 by Adam Michael Bauer, Lucas R. Vargas Zeppetello, Cristian Proistosescu · 1 voice
Environmental Science · Earth and Planetary Sciences · #Climate variability and models #Meteorological Phenomena and Simulations #Climate change and permafrost
paper · doi:10.1175/jcli-d-24-0624.1
Abstract Heat waves are expected to increase in severity and frequency under climate change. Case studies have shown that heat waves typically occur during a coalescence of anomalous atmospheric and land surface conditions, but teasing apart the different contributing factors is a challenge, in part owing to the difficulty in disentangling the role of soil moisture from that of atmospheric variations in solar radiation and thermal advection. Here, we provide evidence that low soil moisture is associated with extremely high temperatures in the midlatitudes and develops a theoretical framework to understand this association. We first show that a nonlinear relationship between soil moisture and temperature arises from energy and mass conservation at the land surface and then employ this relationship to quantify the influence of soil moisture on temperature variability. After deriving a diagnostic equation for the nonlinear temperature response to soil moisture variations, we obtain a dynamical Hasselmann-like model for the soil moisture variations themselves. We find that soil moisture fluctuations control the frequency of temperature extremes by slowly altering the land surface climate state on which atmospheric variability is superimposed, rather than by altering atmospheric variability itself. Our diagnostic model allows us to quantify how extreme an atmospheric anomaly needs to be to create a heat wave, conditional on the underlying soil moisture. By forcing our Hasselmann-like model for soil moisture with stochastic precipitation, we derive analytical solutions for the statistical moments of soil moisture. Significance Statement Heat waves strain numerous aspects of human and natural systems. Here, we present an analytical, minimal complexity model to understand how each of these factors contributes to heat waves in the midlatitudes. Our model yields two novel theoretical insights: 1) a nonlinear diagnostic equation for surface temperatures in terms of surface soil moisture content and 2) a nonlinear Hasselmann-like model for the soil moisture response to precipitation. We further show that the strength of this nonlinearity controls the heterogeneous influence of soil moisture on temperature extremes. Our model provides a conceptual understanding of how “fast” atmospheric variability and “slow” variability in land hydrology jointly contribute to temperature extremes in the midlatitudes.