The Influence Of Land Use Change On Runoff In Guanting Reservoir Basin Based On SWAT Mode

In recent decades,the increasing demand for agricultural irrigation and industrial water in the Guanting reservoir basin has seriously exceeded the local precipitation,resulting in a situation of water resource shortage.The average annual inflow of Guanting reservoir decreased from 26.76 m~3/s(1970-1980)to 4.61 m~3/s(2008-2016),with a decrease rate of 82%.At the same time,with the development of urbanization,in the Guanting reservoir basin,there have been great changes in land use,land use situation of the surface plays an important role in the process of hydrologic cycle.Not only can change the flow of time and space distribution characteristics of river network directly,but also can be done by different infiltration rate,evaporation and other factors,groundwater runoff.Therefore,it is necessary to understand the interaction between local land use change and hydrology in order to develop a reasonable sustainable water use scheme.This paper studies the impact of land use change in Guanting reservoir basin on surface runoff,analyzing the change of land use in the study area in the past 30 years,simulating the hydrological process of the basin with SWAT model,analyzing the impact of land use change on runoff,and predicting the future land use situation and runoff.This study mainly includes three aspects:(1)The land use map of the Guanting reservoir basin in 1987,2002 and 2017 were obtained through the interpretation of ENVI,and the changes of land use types in the past30 years were analyzed.The research shows that the water body in Guanting reservoir basin has not changed significantly in the past 30 years,and the total water body remains at about 0.5%.The forestland area decreased gradually,from 46.68%to 42.13%in 1987to 2002,and from 42.13%to 38.42%in 2002 to 2017,with a decrease rate of 4%.The cultivated area increased significantly from 31%to 49.44%from 1987 to 2002,with an increase of 18.44%.It remained unchanged from 2002 to 2017.From 1987 to 2002,the unused land area decreased significantly,from 9.72%to 2.32%,it is 0.77%in 2017,which basically disappeared.The construction land area changed little from 1987 to 2002,but increased significantly from 2002 to 2017,from 2.91%to 6.85%.Idrisi software was used to construct Markov-ca model to predict land use map in the next 30 years and analyze the future land use type area change.The research shows that after 30 years,the construction land area increases by 4.4%,the forestland area decreases by 7.1%,the change range of other land use types is small,the change range of cultivated land and grassland area is less than 1%,and the change range of water body and unused land area is less than 0.5%.(2)The SWAT model of the base period(1970-1980)was constructed,and the runoff data of the two hydrological stations nearest to the Guanting reservoir,xiangshuipu station and shixuanli station were selected.The SWAT-CUP software was used to calibrate and verificate the model,and the simulation warm-up period was set from 1970to 1972,the calibration period from 1973 to 1976,and the verification period from 1977to 1980.The results showed that the R~2of xiangshuipu station during the calibration period and the verification period were 0.92 and 0.88,and the NES were 0.84 and 0.75,respectively.The of R~2 calibration period and verification period of shixiali station are0.94 and 0.94 respectively,and the NES are 0.86 and 0.81 respectively.The accuracy of model simulation for all evaluation indexes indicates that the SWAT model can be applied to this watershed and can simulate the runoff well,which lays a foundation for the follow-up study on the impact of land use change on runoff.(3)The land use in 2002 and 2017 was brought into the calibrated SWAT model by using the single-factor change method,and the models S1 and S2 in two different land use scenarios were constructed.Compared with the simulated runoff in S0 in the base period,the influence of land use change on runoff was obtained.The results show that the change of land use in Guanting reservoir basin has an obvious impact on runoff:comparing with S1 scenario and S0 scenario,the average annual inflow runof decreased from 839 million m~3 to 519 million m~3,a decrease of 38.1%.The change of runoff caused by land use change accounted for 67.1%of the actual runoff change.comparing with S2scenario and S0 scenario,the average annual runoff dropped from 839 million m~3 to 565million m~3,a decrease of 61.0%.The change in runoff caused by land use change accounted for 38.1%of the actual change in runoff.The predicte land use map was substituted into the calibrated model to complete the prediction and simulation of runoff,and it is found that under the future land use scenario,the inflow of guanting reservoir would decrease by about 30%.