Effects of Changes in Freeze-Thaw Cycles on Soil Hydrothermal Dynamics and Erosion Degradation Under Global Warming in the Black Soil Region

Abstract

Global warming can change the freeze-thaw cycles (FTCs) in seasonally frozen ground and influence soil and water conservation. This study employed an enhanced SWAT-FT (Soil and Water Assessment Tool-FTCs) model to explore the effects of different future climate change scenarios on the FTCs, soil hydrothermal dynamics, and soil erosion in the Upper Mississippi River Basin (UMRB), a typical black soil region with seasonally frozen ground. Results suggested that SWAT-FT could more representatively simulate soil hydrothermal dynamics and soil erosion compared to SWAT. The SWAT-FT simulations revealed that soil temperature in 0–100 cm soil layers of the UMRB could increase by approximately 2°C–4°C during the FTCs period under SSP5-8.5 in the mid to late 21st century, decreasing the freezing days (FD) and even the absence of FTCs in some southern zones, but an increase in FD for some central zones. These changes were affected by air temperature, soil water content, and snow cover, resulting in three dominant response patterns of soil hydrothermal dynamics to global warming during the FTCs period in the UMRB, which were lag symmetric response in the northern zones, non-symmetric response in the central zones, and rapid symmetric response in the southern zones. The alterations in soil hydrothermal dynamics due to global warming exacerbated soil erosion in early spring after the FTCs by 2.3 times under SSP5-8.5 in 2071–2100 compared to the baseline scenario (1985–2014). Moreover, the erosion pattern converted from “dual-peak” to “single-peak” in April or May, increasing challenges of spring erosion control.