Study On Hydrological Impact Of Watershed Land Use Based On Hydrological Models And Complementary Relationships

The upper reach of the Han River is the core water source of the national mid-route project of South-to-North Water Transfer.Its land use and its changes are related to the water safety and ecological environment of the water source area and the water receiving area.Wei Rives Basin is a typical water shortage area.The Guanzhong Plain where Wei River flow is an important cconomic area in the north.The response of the drological cycle of the Han River and Wei River basins on two sides of Qinling Mountains to future climate changes will affect the formulation of land use policies.Both catchments are very scnsitive to climate change feedback.A modeling framework to close the feedback of cvapotranspiraticon into the atmosphere(FCEA framework)based on the generalized cvapotranspiration complementary relationship was established in this study.The impact of land use change on runoff and evaporation under different land use scenarios was analyzed in the study area of Han River and Wei River.This has practical significance for realizing sustainable development of catchment and improving land use planning policies of catchment.This study takes the upstream walershed of Han River as the research area,and the upstream watershed of Wei River as the comparative study area,and reveals the evolution law of hydrometeorological elements and land use in the study area,The applieability pf SWAT model in the study area of Han River and Wei River is evaluated.An evaporation complementary model that is suitable for the study area was selected to estimate the actual evaporation of the study area.The FCEA framework was established to simulate the evapotranspiration feedback to the atmosphere based on evaporation complementary relationship in various land use scenarios,and to discuss the hydrological impact of land use changes on runoff and evapotranspiration.Finally,various calculatios methods and different evaporation products are used to evaluate the actual evaporation in the study area.The main conclusions are as follows:(1)The evolution laws of precipitation,runoff,and land use in the study area were revealed by linear regression,cumulative offset and ordered cluster analysis.From 1972 to 2017,annual precipitation and annual runoff depth in the study area of Han River showed non-significant decrease trend,both of which had a sudden change in 1990.The mean annual precipitation of the watershed was 873.4mm and the mean annual runoff depth was 408.6mm.Annual precipitation and annual runoff depth in the study area of Wei River showed non-significant increase trend from 2001 to 2017,and there was no sudden change.The mean annual precipitation of the watershed was 486.9mm and the mean annual runoff depth was 26.20mm.The main land use types in the study areas of Han River and Wei River are woodland,grassland and farmland and the land use changes appeared among woodland,grassland and farmland.The area of grassland,construction land,water area and unused land in the study area of Han River is increasing,while the area of woodland and farmland is decreasing.The largest area of land use changed from farmland.The area of grassland,farmland,construction land and water area in the study area of Wei River is increasing,while the area of woodland and unused land is decreasing.The largest area of land use changed from grassland.(2)SWAT hydrological model was constructed based on underlying surface data and hydrometeorological data in the study areas of Han River and Wei River,and the observed daily runoff was used for the parameter calibration and verification.The results show that the most sensitive parameter is runoff curve coefficient CN2.The NSE coefficient,deterministic coefficient and KGE coefficient of the simulated daily flow are all larger than 0.71 in the study area of Han River,and larger than 0.54 in the study area of Wei River.SWAT model has good applicability in the study areas of Han River and Wei River.(3)Based on the principle of evaporation complementarity and the water balance method,parameters of several evaporation complementarity models are calibrated,and the applicability of evaporation complementarity models,B2015 model and H2018 model,in the study area are compared.The theory of complementary evaporation is applicable in both the study areas of Han River and Wei River.After the calibration,both B2015 model and H2018 model have good performance in the estimation of actual evaporation in the study areas.The relative errors compared with water balance result are less than 8%,and B2015 model has the smaller relative error in estimating actual evaporation.B2015 model is selected for the following calculation.(4)Based on SWAT model and B2015 model,a modeling framework to close the feedback of evapotranspiration into the atmosphere(FCEA)based on the generalized evapotranspiration complementary relationship was constructed to study the impact of different land use changes on runoff and evaporation in the study areas of Han River and Wei River.Under the baseline scenario of Han River,the annual actual evapotranspiration is 496.3 mm when the result tends to be stable.Current land use types and climate tend to be stable,but they have not yet reached a complete equilibrium state.In scenario 1,2 and 5,the runoff reduced after multiple iterations among 7 land use scenarios.The runoff increased after multiple iterations in scenario 3,4,6 and 7.In the 7 scenarios,the PET in the final simulation is smaller than that in the initial simulation except scenario 4.In baseline scenarios,scenarios 1,2 and 5,the final simulated ATE is greater than the initial simulated ATE,while in other scenarios it is smaller than the initial simulated ATE.The actual evapotranspiration is 458.9 mm when the simulation results tend to be stable in Wei River.Current land use types and climate tend to be stable and reach the equilibrium state.Iterative simulation results of 7 scenarios in Wei River are quite consistent.Compared with the initial annual runoff,the runoff of 7 scenarios increases after multiple iterations.The PET and AET values in the final simulation are smaller than those in the initial simulation.(5)Quantitative analysis of actual evapotranspiration of the two study areas is carried out by using various calculation methods and actual evaporation products.The results show that the actual evapotranspiration calculated by water balance method,B2015 model and SWAT model are close.The actual evaporation calculated by water balance method and SWAT model is closer to the actual value.The calculated value of B2015 evaporation complementary model is 3.79%and 2.46%smaller than that of water balance method in Han River and Wei River,respectively.The actual evaporation of TED AC and GLDAS products is 31.08%and 36.54%larger in Han River and 13.72%and 5.06%larger in Wei River.Their evaluation performance in Wei River is better than that in Han River.The correlation coefficient of annual actual evaporation of TED AC and B2015 models is the highest,and they are 0.37 and 0.54 in Han River and Wei River,respectively.