| In the last one hundred years,with the high-intensity interference of human activities on the atmosphere and underlying surface,global climate warming has become more obvious,and the hydrometeorological links such as precipitation,evaporation,and runoff in the watershed have been directly affected.Precipitation and potential evapotranspiration are the most important meteorological input data for hydrological simulation.Evaluation of the applicability of hydrological simulation of potential evapotranspiration and precipitation data obtained by different methods is of great value in revealing the law of runoff generation in the river basin under changing environments,and is of great value to the ecology protection and water security of the Yellow River Basin.Research on the time-varying characteristics of hydrological model parameters in the "unsteady state" basin,and establishment of a model parameter estimation method that can reflect the characteristics changes in the basin,will improve the simulation and prediction accuracy of the hydrological model in a changing environment to a certain extent.In this study,the upstream catchment of the Beidao hydrological station of the Weihe River was used as the study area.First,the temporal and spatial evolution law of the ecological hydrometeorological elements in the study area was analyzed;then,based on the distributed hydrological model SWAT,the potential evapotranspiration data of different estimation methods were analyzed in the Weihe River.Based on the measured precipitation data of the ground station,the multi-scale accuracy of CMFD,MSWEP,and CMADS precipitation products in the study area is evaluated.Two parameter scenarios were set up to test the effectiveness of different precipitation products in SWAT model.Finally,the time-varying parameter sequences of the hydrological model were obtained through segmented calibration,and the relationship of the model parameters to the watershed precipitation,potential evapotranspiration,and NDVI were analyzed.The main research results obtained are as follows:(1)Aiming at the precipitation,potential evapotranspiration,temperature,runoff,vegetation index and other factors in the study area,the linear regression method and cumulative anomaly method are used to reveal the evolution law of the ecological,hydrometeorological elements of the basin.The results show that the annual precipitation from 1965 to 2017 showed a decreasing trend,and the annual potential evapotranspiration,annual average temperature and annual runoff all showed an increasing trend.The annual potential evapotranspiration had a significant abrupt change around 1994,and significant abrupt change of the annual average temperature occurred around 1997.The average annual NDVI value showed a significant increasing trend,and the vegetation coverage was significantly improved after 2011.From 2001 to 2017,the average annual NDVI value of the basin increased by 19.7%.(2)Based on the underlying surface data of the upstream catchment of the Beidao Hydrological Station and the hydrometeorological data from 2001 to 2017,SWAT hydrological model was constructed,and the parameters were calibrated and verified in the daily runoff simulation.The results show that there are 6 sensitive parameters,among which the most sensitive parameter is the number of runoff curves CN2.Except for a few years,the simulated daily runoff of the Beidao Hydrological Station can well represent the daily flow process.The deterministic coefficient R2,Nash-Sutcliffe efficiency coefficient and KGE coefficient are all larger than 0.54,which can meet the accuracy requirements of hydrological simulation.The SWAT model has good applicability in the upper reach of the Weihe River.(3)The study adopted the Penman-Monteith method(PETP-M)and evaporation data of E-601 type evaporation pan(PET601)to drive the SWAT model respectively,and use the SUFI-2 optimization algorithm for parameter sensitivity analysis,model calibration,verification and uncertainty analysis.The results show that the potential evapotranspiration obtained by different methods are quite different.The potential evapotranspiration of the PET601 method is lower than the Penman-Monteith method,but they all have similar intra-annual distributions.Using PETP-M and PET601 to drive the hydrological model to simulate the runoff process,the hydrological simulation accuracy is better,and the PET601 method is more suitable for the Weihe River Basin.The impact of potential evapotranspiration deviations on the hydrological simulation is significantly weakened by the adjustment of model parameters.(4)Combined with the observation data of ground stations in the study area,the multi-source fusion precipitation data CMFD,MSWEP,and atmospheric assimilation data CMADS are quantitatively analyzed for multi-temporal and spatial scale accuracy.These three sets of precipitation data can basically reflect the spatial distribution of precipitation in the basin.But there is a deviation to the extent.MSWEP performs better in the comparison of precipitation at various time scales,and the average error on the daily scale is only 0.05 mm.The SWAT model driven by each precipitation product can simulate the daily flow process of the upper reach of the Weihe River.The simulation accuracy after calibrating the parameters for each precipitation product is significantly better than the results of the same parameter set.These precipitation products can replace the precipitation data at the ground stations in the hydrological simulation of the Weihe River Basin.(5)The SWAT model was calibrated in time interval of one year.The time-varying parameter sequence of the hydrological model was obtained,and the relationship of the four parameters to the watershed precipitation,potential evapotranspiration,and NDVI were analyzed.The model parameters fluctuate over time during the study period,and the change of the parameter ESCO is the same with the increasing trend of annual evaporation in the basin.The model parameters all show a certain correlation with the potential evaporation of the basin,indicating that the changes of hydrological model parameters in the upper Weihe River basin are closely related to the changes of potential evapotranspiration.Therefore,the potential evapotranspiration can be used as a characteristic factor for the dynamic changes of model parameters. |
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