Spatiotemporal dynamics and scale-dependent similarity of soil moisture on hillslopes in the Mu Us Sandy Land, China

Study region Mu Us Sandy Land, China Study focus This study investigated soil moisture similarity and scale-dependent dynamics on sandy hillslopes using hourly observations from windward and leeward slopes at multiple depths and slope positions. Spearman’s rank correlation was used to assess overall temporal similarity among soil layers. Wavelet coherency analysis was then applied to examine time- and scale-dependent relationships among soil moisture series and between soil moisture and rainfall or potential evapotranspiration. The results were evaluated using correlation coefficients, average wavelet coherence (AWC), percentage area of significant coherence (PASC), and phase relationships. New hydrological insights for the region Soil moisture similarity generally decreased with increasing depth interval. Spearman’s correlation coefficients ranged from 0.394 to 0.9 on the windward slope and from −0.011 to 0.775 on the leeward slope, indicating stronger vertical coupling on the windward slope. AWC and PASC further showed that coherency between surface and deeper layers weakened with depth. Rainfall controlled wet-season soil moisture variability across multiple scales, whereas potential evapotranspiration was more closely related to dry and freeze–thaw periods, especially at 12–24 h scales. Phase relationships indicated delayed vertical infiltration and lateral redistribution toward footslope positions during wet periods.