Spatial-temporal Differences Of Hydrologic Parameters In SWAT Model

The key of distributed hydrological model successfully applying a basin depends on the identificated accuracy of parameters sensitivity and their values,which means whether the parameters sensitivity and their values can truly reflect the basin characteristics of climate and underlying surface and describe the true hydrological processes of the basin.As a typical semi-distributed hydrolbgical model,SWAT model is widely used in China and abroad.However,SWAT model also has the problem of having too many parameters to be calibrated.Combining with the characteristics of climate and underlying surface and discussing the spatial-temporal differences of runoff process parameters of SWAT model has important theoretical and practical significance to reveal the law of hydrological process,improve the accuracy of model simulation and extend the scope of application of SWAT modelThis paper selected Jinjiang basin in southeastern China with subtropical monsoon climate and the Barrett basin in e west coast of the United States with Mediterranean climate as the tipical study areas.Based on the estibishment of the two basins with large variability on climate and underlying surface and the simulation of mothly runoff,the differences of SWAT runoff parameters and their influencing factors of the two basins was analysed.On the other hand,this paper collected the article of SW}AT model applying in domestic watershed in recent years.In special aspects,all of the collected basins were divided into four regions(humid,semi-humid,semi-arid,arid)according to drought index,while in temperal aspecst,wet and dry seasons and wet and dry years were divided.All were to analiyse the spatial-temporal differences of SWAT model runoff parameters sensitivity and its values.The results showed that:(1)SWAT model can simulate the monthly runoff of Jinjiang basin and Barrett basin well and the runoff simulation efficiency of Jinjiang River Basin is higher than that of Barrett River Basin.(2)The sensitivity and value of SWAT model runoff parameteIrs have some regional differences under the influence of precpitation,temperature,soil,vegetation cover,terrain and other climate and underlying surface factors.The sensitivity of surface runoff parameters is the strongest,followed by groundwater parameters,and snow melt parameters are the weakest;CN2,ESCO and SOL_AWC have strong sensitivity in most of regions and SOL_AWC has less impact on runoff in arid regions because of less rainfall and deficit of soil water.;The sensitivity ofALPHA_BF and GW_DELAY in arid regions are slightly higher than that in other regions;The sensitivity of snow melt parameters in arid regions are higher than that in other three regions;Conpared with other snow melt parameters,TIMP,SMFMX,SMFMN and SMTMP show strong sensitivity in arid regions.The regularity of differences of SWAT runoff process parameters between Jinjiang basin and Barrett basin was similar to the conclusion.(3)The sensitivity and values ofsome SWAT runoff parameters were different between wet and dry seasons,which indicates there may be some differences in hydrological processes(such as surface runofl;soil evaporation,groundwater recharge runoff and river convergence etc.)(4)When there was a large inter-annual variability of runoff,SWAT model with the traditional calibration had low simulation efficiency during the dry years,and did not meet the performance requirements;Calibration by separating wet and dry years greatly improved the SWAT model's simulation efficiency of monthly runoff in the dry years and also improved the simulation results for the wet years and the entire series.(5)Six main sensitive parameters of SWAT model(ALPHA_BF,CH_K2,CN2,ESCO,GWQMN and SOL_AWC)were different between the wet and dry years,which indicated that the hydrological conditions or responses in this watershed were different between the wet and dry years.