Quantifying seasonal shifts in soil thermo-hydrological coupling using a TMS-4 sensor and ERA5-Land data

Abstract

Forest ecosystem functions are influenced by the dynamic interplay between soil temperature and moisture. However, the lack of high-resolution temporal data has caused constraints in the comprehensive investigation of their association over time. This study uses a full annual cycle of 15-minute microclimate data, captured by a TMS-4 datalogger in Postăvaru, Romania, to quantify the correlation between soil temperature and moisture across different seasons, investigate seasonal regime shifts in soil thermo-hydrological processes, and quantify the thermal buffering capacity of soil moisture. Our analysis has shown a reversal in the soil temperature-moisture relationship across seasons. While the annual correlation was inverse (r = -0.42), a strong positive winter correlation (r = +0.606) was observed due to the melting of frozen water, which contrasted sharply with the strongly negative autumn correlation (r = -0.781) driven by evaporation. We further analyzed the role of soil moisture as a thermal buffer, which reduces soil temperature by 0.31°C per 1% volumetric water content increase. The rate dynamics also showed how soil cooling and wetting were faster than warming and drying. These findings indicate the potential of high-frequency monitoring in long-term continuous monitoring of the soil temperature-moisture relationship that may challenge the conventional static models. Also, this study may highlight that soil temperature-moisture coupling is seasonally dependent, with implications for predicting ecosystem responses to climate change and informing sustainable forest management.