Geostatistical analysis of soil moisture variability on Da Nangou catchment of the loess plateau, China

To achieve a better understanding of environmental issues related to soil e rosion, flooding, and solute transport, it is necessary to understand the v ariability of soil moisture under different climatic and geological conditi ons and at different spatio-temporal scales. Moisture patterns based on fiv e depths (0-5, 15-20, 25-30, 45-50, and 70-75 cm) were determined in the Da Nangou catchment of the loess plateau of China from May to September 1999. Spatial structure of profile-averaged and layer-averaged soil moisture was analysed using semivariograms. The results indicated that soil moisture ex hibits changing spatial dependence with time and depth. For profile-average d soil moisture, high sills [4.6-14 %(v/v)(2)] and high ranges (135-160 m) were observed during dry conditions. The sills [2.6-6.3 (%v/v)(2)] and rang es (140 m) were small during wet conditions. However, soil moisture was des cribed by linear semivariograms without a sill following a significant rain event. For layer-averaged soil moisture, the sills increased with depth, b ut not for the ranges. The nuggets tended to increase with higher sills. Th is analysis provides insights into the variability of soil moisture on a la rge scale and interpolation strategies for extrapolating point measurements across the catchment.