Understanding the influence of soil moisture on heatwave characteristics in the contiguous United States

Abstract

In the context of global climate change, heatwaves are becoming increasingly significant because of the adverse impacts on human health and ecosystems. However, the quantification of heatwaves relies on different temperature metrics, and little is known about how the different types of heatwaves are affected by soil moisture. Using a set of observational datasets during the period 1981–2020, this study investigates the characteristics of warm-season heatwaves over the contiguous United States (CONUS) derived from three different temperature metrics (temperature, wet-bulb temperature, and equivalent temperature), and examines how different types of heatwaves are associated with soil moisture. Increasing trends of all types of heatwaves are observed in most parts of CONUS except for the central US, posing potential risks to human health. Due to limited evaporative cooling over dry soil, there is a substantial negative relationship between soil moisture and temperature-only heatwaves across the CONUS. Meanwhile, in some regions of the western and central CONUS, there is an evident positive relationship between soil moisture and humidity-included heatwaves, which represent the combined effects of temperature and humidity. The event-based analysis in Nebraska emphasizes that temperature-only heatwaves occur over relatively dry soil conditions, while humid heatwaves tend to occur over somewhat wet soil. Our results highlight the importance of considering different types of heatwaves and their relationship with soil moisture from the land-atmosphere coupling perspective, offering valuable insights for local and regional climate planning and mitigation.