Temporal stability and variability of field scale soil moisture on mountainous hillslopes in Northeast Asia

Abstract

Soil moisture is a crucial component in the hydrologic cycle. The analysis of soil moisture variability is challenging because soil moisture is dependent on physical factors such as: antecedent precipitation, soil texture, land cover, and topography. This study investigated soil moisture variability, validated the utility of temporal stability analysis for measuring areal mean soil moisture, and identified factors that were strongly related to temporal stability characteristics at small mountainous sites in Northeast Asia. Soil moisture contents were measured at different depths using time domain reflectometers at two fields in the center of Korea. Time series analyses showed that slope played a substantial role on soil moisture distribution. The Chi-square test identified Gumbel distribution as an optimal soil moisture distribution. The mean and the standard deviation of soil moisture showed an upper convex shape and the variability of soil moisture was highest at moderate mean soil moisture conditions (~15–20%) at 10, 30, and 60cm in the study sites. Temporal stability analysis revealed the representativeness of the average volumetric soil moisture contents with errors of ±4.91% and ±2.35% for the fields of Sulma and Chongmi river basins, respectively. Analysis of variance and Tukey's honestly significant difference tests showed that the slope and soil texture, particularly clay, had an impact on the temporal stability characteristics of soil moisture for the study sites, the land cover had no significant impact. Temporally stable locations for soil moisture were determined with the milder slope and higher clay contents at the study sites.