Analysis On Runoff Change In The Miyun Reservoir Basin Based On The Improved Xin’anjiang Model

Hydrological model is a significant tool to study the hydrologic cycle process and the evolution law of water resources,which can provide technical support for solving water problems.As an important part of the hydrological model,the change process of soil infiltration shows great spatial and temporal variability and scale dependence.It is of great significance to analyze the infiltration law of typical soils in watershed to determine the range of parameters and improve the accuracy of hydrological model.Due to the combined influence of climate change and human activities,the water cycle process in the river basin has changed significantly.Applying hydrological model method and water balance method to analyze the attribution of runoff change can provide a basis for water resources planning and management in the river basin.In this paper,the Chaobaihe River Basin in the upstream of the Miyun Reservoir is taken as the survey region.Firstly,the double-loop method is used to determine the typical soil moisture infiltration process in the test area,and the infiltration curve fitted by the test is introduced into the Xin’anjiang model.Then,the particle swarm optimization algorithm is introduced to determine the parameters of the improved Xin’anjiang model and applied to the simulation of floods.Subsequently,methods such as the year mutation test,inter-annual trend analysis and periodic oscillation analysis are used to study the variation characteristics of hydrometeorological elements in multiple time scales.Finally,the base period and the change period are divided by the mutation year of the annual runoff,the improved Xin’anjiang model and the elasticity method based on the Budyko hypothesis are used to evaluate the impact of climate change and human activities on the runoff change of the Miyun Reservoir River Basin.The main research conclusions are as follows:(1)The Philip model,Horton model,and Kostiakov model are able to describe the vertical permeability of unsaturated soils in the test area,and the Philip model has the best fitted model for simulating soil infiltration.The variation range ratios of soil characteristic parameters all show moderate variation intensity,and the probability distribution of the parameters follow the normal distribution or the lognormal distribution.(2)Compared with the original model,the improved Xin’anjiang model is closer to the actual measured process for the simulation of each flood process.The obtained simulation process based on the parameters optimized by the particle swarm optimization algorithm has a good fit with the actual process,which shows the feasibility of this algorithm in the parameter optimization as far as the improved Xin’anjiang model concerned.(3)The annual potential evaporation in the Chaobaihe River Basin showed a slight upward trend,while the annual runoff showed a significant downward trend.The mutation year of annual runoff in the Chaohe River Basin is 1998,and its variation cycle is 7a.The mutation year of annual runoff in the Baihe River Basin is 1979,and and its variation cycle are 7a and 18 a.(4)Applying the improved Xin’anjiang model,the contribution rates of climate change and human activities to the runoff changes in the Chaohe River Basin are 36.5% and 63.5%,while the contribution rates in the Baihe River Basin are 26.0% and 74.0%,respectively.Using the elastic coefficient method based on the Budyko hypothesis,the average contribution rates of climate change and human activities to runoff changes in the Chaohe River Basin are 64.9% and 35.1%,respectively,while the average contribution rates in the Baihe River Basin are 20.6% and 79.4%,respectively.