Development of a large-scale hydrological model TOPX and its coupling with regional integrated environment modeling system RIEMS

On the basis of the improved SIMTOP runoff parameterization scheme and the calculating method of three-layer soil moisture balance in Xinanjiang model, this paper developed a simple but highly-efficient large-scale hydrological model (TOPX), which can provide the function of scaling transformation on topographic index. Although the TOPX model has less data input and minimum parameters for calibrating, it can better describe the two-dimensional hydrological processes. Then TOPX was coupled with the Regional Integrated Environment Modeling System (RIEMS) to enforce its ability of numerical simulation for the runoff in large-scale watershed. The results of the offline test performed at Youshui River catchment indicate that the TOPX model produced better simulation effect of daily runoff in small sized catchments and it can describe the various hydrological processes of watershed. The offline test of Jinghe basin shows that TOPX model has the better ability of distributed simulation at large-scale and it can capture the major characteristics of land-surface hydrological processes at regional-scale. Then the coupling model of RIEMS and TOPX was still online tested in Jinghe basin. By means of the scale transformation scheme on topographic index and the yielding and runoff routing theory, the coupling model uses the meteorological data simulated by a regional climate model to drive the hydrological model for predicting the daily runoff at large-scale watershed. A further analysis revealed that the accuracy of the distributed rainfall data simulated by the regional climate model (RIEMS) is the crucial factor to affect the modeled runoff in the coupling model (RIEMS_TOPX).