Study on Parameters Estimation of the XAJ Model Based on Underlying surface characteristics

Hydrological models are essential in accessing hydrological processes at both hillslope and watershed scale. The Xin'anjiang(XAJ) model is a conceptually-based model which was developed on the basis of conception of hillslope hydrology. As the key model parameter, the tension water capacity has rigid physical definitions which in principal can be estimated by watershed characteristics. Due to the limitation of previous knowledge and data, the tension water capacity was determined mainly by calibration with complete high-quality data, which hinders the application of XAJ model in the ungauged watershed and the development in the distributed direction, so it's necessary to do some study on parameters estimation. In this study, we first investigated the three quantitative approaches to estimate the thickness of unsaturated zone based on topographic features, soil characteristics and vegetation cover, respectively. We employed derived unsaturated zone thickness together with other underlying surface characteristics to investigate the tension water capacity estimation. Our results shows that the overall performance of the XAJ model is more stable and robust than that of the calibration, and more suitable to be applied in the ungauged catchments.