ABSTRACT The vadose zone, a critical interface in terrestrial ecosystems, exhibits dynamic responses to hydrological events, fundamentally altering energy and water transport. This study employs principal component analysis (PCA) to investigate the intricate relationships among meteorological factors, soil heat flux and soil moisture content within the vadose zone, specifically contrasting conditions before and after a significant rainfall event. Hourly data, collected over 3 days pre‐ and post‐rainfall for five distinct variable groups. Pre‐rainfall (dry) conditions revealed a system primarily driven by atmospheric energy inputs, where solar radiation and air temperature exerted dominant control over near‐surface thermal dynamics and distinct soil moisture profiles. In stark contrast, post‐rainfall (wet) conditions demonstrated a profound shift to water‐driven dynamics. Here, soil moisture content became the overwhelming dominant factor, showing remarkable homogenisation across depths due to widespread infiltration. Heat transfer pathways were significantly altered, with deeper soil heat flux exhibiting distinct behaviours from the surface, indicative of water's buffering effect on thermal properties. Furthermore, atmospheric pressure's influence gained prominence in the post‐rainfall period, suggesting its role in longer‐term hydrological stability. This comparative PCA elucidates the systemic reorganization of vadose zone processes in response to water infiltration, transitioning from an energy‐limited to a water‐saturated state. These findings are pivotal for refining coupled hydrological and thermal models, enhancing predictions of groundwater recharge, evapotranspiration and soil thermal regimes in varying climatic contexts.
David Ching‐Fang Shih (Wed,) studied this question.