A Simple Water Balance Model for a Mesoscale Catchment Based on Heterogeneous Soil Water Storage Capacity

Abstract

The work presented in this paper has been motivated by the need to develop a simple parameterization method for rainfall-runoff modelling considering spatial heterogeneity. A concept of tension water storage capacity distribution has been incorporated into a rainfall-runoff model to explain the runoff generation phenomenon more realistically. Originally, the concept was initiated by Zhao et al. (1980) in the Xinanjiang model, and later adopted by many researchers, e.g., in the VIC model by Wood et al. (1992). However, the expression for the tension water storage distribution in the Xinanjiang model is unable to describe all the situations in natural catchments. We therefore propose a general expression for the tension water storage capacity distribution. Applying this general expression, we have compared the performances of four kinds of rainfall-runoff simulation models, which are, the VIC model (Model 1), the unconfined version of VIC model (Model 2), and two models with a different concept of runoff generation mechanism with confined (Model 3) and unconfined (Model 4) aquifer cases, for the mesoscale catchments of Japan and Thailand. Sensitivity analysis of the model parameters has been conducted as well. The effect of time and spatial scale is also brought out. As a result, we can say that Model 3 and Model 4 indicate better runoff estimation and realistic soil-water storage time series, whereas, Model 1 and Model 2 are not able to represent a realistic time series of soil-water storage.