An improved method that incorporates the estimated runoff for peak discharge prediction on the Chinese Loess Plateau

An accurate prediction of peak discharge in watersheds is critical not only for water resource manage-ment,but also for understanding the complex relationships of hydrological processes.In this study,a modified peak discharge formula based on the Chemicals,Runoff,and Erosion from Agricultural Man-agement Systems(CREAMS)model was developed by introducing rainfall intensity and soil moisture factors.The reliability of the proposed method was tested with data from 1464 storm events in 41 watersheds and was applied to 256 storm events in five remaining typical watersheds using the opti-mized parameters.The results indicate that the proposed method is highly accurate in terms of model efficiency,as determined by Nash-Sutcliffe efficiencies(NSEs)of 88.60%,74.04%,and 90.12%during the calibration,validation,and application cases,respectively.Furthermore,it performed better than the original and modified CREAMS methods.Subsequently,using the parameters derived from the initial 41 watersheds and the runoff estimated using the modified Soil Conservation Service curve number(SCS-CN)method,the proposed method was used to predict the peak discharge from the last five typical watersheds.Large NSE(63.88-80.83%)and low root mean square error(RMSE)values(0.31-35.93 m^(3)s^(-1))were obtained for the five watersheds.Overall,the proposed peak discharge model,combined with the modified SCS-CN method,may accurately predict event-based peak discharge and runoff for general applications under various hydrological and geomorphic conditions in the Loess Plateau region.

Predictions of soil and nutrient losses using a modified SWAT model in a large hilly-gully watershed of the Chinese Loess Plateau

Hydrological models are effective tools for assessing the effects of soil and nutrient losses on land degradation.SWAT(Soil and Water Assessment Tool)model is widely used to simulate soil and nutrient losses caused by various management regimes.However,its performance of predicting nutrient loss has not been assessed adequately on the Loess Plateau.This study proposed a modified SWAT model by incorporating the modified Soil Conservation Service curve number method,the storm-based Chinese soil loss equation and the nutrient loss model.The observed daily data of runoff and sediment over 16 years and the monthly soluble phosphorus(P)and nitrate losses over 9 years and 4 years,respectively at the outlet of the upper Beiluo river(UBR)basin were used to assess the model performances.Global sensitivity and uncertainty analyses of parameters to runoff,sediment,soluble P and nitrate in the modified SWAT were conducted.The findings during calibration and validation showed that the modified SWAT was highly accurate in terms of model efficiency(calibration:0.83,0.83,0.48,and 0.49;validation:0.58,0.57,0.53,and 0.65)for runoff,sediment,soluble P loss and nitrate loss,respectively.High model efficiency indicated that the modified SWAT could accurately predict soil and nutrient losses at the river basin scale for the Loess Plateau.Moreover,the temporal variations from month to year and the spatial variations at the sub-basin scale for soil loss and the total N and P losses were analysed using the data simulated by the modified SWAT.The results indicated that the critical loss period occurred in July and August,and the Grain for Green project significantly affected the hydrological behaviour and reduced the soil and nutrient losses in the UBR basin.