Inverse Analyses of Water Flow in Semi-arid Savannas on Karst Terrain by Hydrus 1D.

In semi-arid savannas on karst terrain, water flow plays an important role in mass and energy transport. However, estimation of hydraulic parameters is a challenge because rocky soil makes it difficult to measure the parameters directly using a core sample method. The objective of this study is to estimate the hydraulic parameters with an inverse method using Hydrus 1D, and to assess the parameters by temporal change in measured water content. The experimental field was a grassland on a shallow stony clay located on the Edwards Plateau in south central Texas. The mean annual air temperature was 19.2^oC, and the annual rainfall was about 829 mm. Water content was measured with ECH₂O probes and evapotranspiration (ET) was measured by the eddy covariance method. Hydraulic parameters of van Genuchten equation were determined by temporal change in water content and ET during winter and summer seasons. Although the hydraulic parameters were estimated successfully for both winter and summer conditions, the difference of the saturated hydraulic conductivities was one order of magnitude. Using the parameters based on summer data, measured and estimated temporal change in water content agreed well through the whole year.