Application and parameters sensitivity analysis of SWAT model.

SWAT(Soil and Water Assessment Tool),a distributed hydrologic model integrated with geographic information system(GIS) to simulate the hydrological processes and runoff generations in mountainous catchments,was applied to the Heihe River basin located in the Qilian Mountains of northwestern China.Simulations at present were preliminarily focused on predicting the continuous daily runoff in a high altitude,cold,semi-arid 10 009 km2 basin with the total control hydrological station of Yingluoxia.Because the sensitivity analysis and calibration is a key and difficult issue of the application and development of the distributed hydrological model and spatial variability,access difficulties model input parameters always contain uncertainty.In this paper,model is calibrated with observed data from four principal hydrologic stations in the Heihe River basin.A simple approach of sensitivity analysis on the prior-determined parameters was used to assess the sensitivity of those parameters to the final performance of the model,the calculated sensitivity indices are ranked into four classes.The laws are discovered that change some important parameters how to affect model results and thus to determine the most sensitive parameter values.The calibration procedures have considerably been simplified,the blindness on the determination of those pre-determined factors was decreased.The runoff generation processes and their calculation principles were described.The basic GIS data layers include the Digital Elevation Model(DEM),soil and land use/cover digital maps generated from the digitalization of the field survey results.Four meteorological stations within or near the study basin were selected to derive the distributed input meteorological parameters.Based on the topographic features,soil and land use/cover distribution patterns,SWAT-GIS delineated the basin into 157 homogeneous hydrologic respondent units(HRU),each of which represents a particular feature of soil and land use/cover combinations within the sub-watershed and a group of parameters was assigned to them for charactering its hydrological responses.The model simulation period was divided into calibration(1990-1995) and validation(1996-2000) periods.Results from the 11 year's simulation suggested a good performance of the model demonstrated by Nath-sutcliffe coefficient R2 of over 0.80 in the rain-rich years and the difference between the observed and simulated runoff was less than 16% in general.