Terrain Attributes as Predictors of Soil Moisture Distribution

Larry C. Guerra¹

ABSTRACT

This study examines the relationship between terrain attributes and soil moisture content in a catchment in southeastern Australia. The analysis was conducted to assess the importance of lateral subsurface flow in the redistribution of soil moisture at different depths of the soil.

Some terrain attributes were found to be statistically significant predictors of soil moisture distribution in the Lockyersleigh Creek catchment. In between storms, there is a particular time when statistically significant relationship between soil moisture content and certain topographic attributes is highest and when most of these terrain attributes give significant relationships. The relationship weakens as the catchment wets up or dries up. Further, there is still a large percentage (>60%) of the variance not accounted for by the regression equation. These results demonstrate the inadequacy of using static terrain attributes such as slope, aspect, upslope contributing area, profile curvature, and plan curvature to predict soil moisture content, which varies not only spatially but also temporally. Results of further analysis indicate that, in the Lockyersleigh Creek catchment, position in the landscape is not as significant in the overall distribution of soil moisture as was originally anticipated. The role of the very slow lateral subsurface flow in the redistribution of soil moisture seems to be confined to depths below 50cm.

¹Assistant Professor, Agrometeorology and Farm Structures Division (AFSD), Institute of Agricultural Engineering (IAE), College of Engineering and Agro-industrial Technology (CEAT), University of the Philippines Los Baños (UPLB)