Study On The Evolution Characteristics Of Hydro-meteorological Factors And Attribution Analysis Of Runoff Change In Weihe River Basin

With the rapid development of the social economy and global climate change,the contradiction between the increase in the demand for water resources by the socio-economic development and the amount of water available from nature provides the most intuitive manifestation of the reduction and dryness of river runoff.This change in river runoff is a comprehensive reflection of changes in the water cycle hydrological elements of the basin.In this context,the Weihe River Basin is used as the research area.Based on the basin water cycle theory,a variety of mathematical statistics methods and SWAT models are used to comprehensively and quantitatively analyze the evolution characteristics of hydrometeorological elements and the attribution of runoff evolution during the water cycle.The research results have important reference functions for watershed ecological environment protection,economic sustainable development and the development and utilization of water resources and land resources in the whole basin.The main research contents and results are as follows:?1?Using the Penman-Monteith formula to calculate the potential evaporation in the basin,and using the sliding average method,M-K trend test,sliding t test and Morlet wavelet to calculate the precipitation,temperature,evaporation and runoff evolution of hydrometeorological elements in the basin.The results show that the precipitation in 1960?2016 shows an insignificant decrease trend,the rate of change is-0.93mm/a,and the average annual precipitation is 541.2mm,which is presented a spatial distribution pattern of less in the northwest and more in the southeast.The potential evaporation and temperature are showed a trend of increase significantly and not significantly.The hydrological stations in the basin showed a significant decrease trend.According to the runoff analysis of change point,the study period is dividied in base period?1960?1970?and change period?1971?2016?.According to the Morlet Wavelet analysis,the period of cycle of abundance and drought is 23 year.There were two complete alternation changes between abundance and drought from 1965 to 2009.?2?The SWAT model is used to simulate the runoff in the Weihe River Basin.According to the characteristics of Weihe River basin,the soil database,meteorological database and relevant data files are firstly prepared for the establishment of SWAT model,in which 121 sub-basins and 850 HRUs are generated.Then the model parameters of different regions controlled by the hydrological station are calibrated step by step by adopting the method of first tributary then main stream,first upstream then downstream.The three indexes of Nash-Suttcliffe efficiency coefficient(E_NS),determination coefficient?R²?and relative deviation?R_E?are used to evaluate the simulation effect of the model.The results show that all stations are above 0.5 of R² and E_NS,the major stations are above 0.8,and the relative deviation is below 25%.SWAT model has good applicability and simulation effect in this area.SWAT model has good applicability and simulation effect in Weihe River basin.?3?Using the land use transfer matrix and GIS overlay layer to analyze the land use change in 1980,2000 and 2015.The change area only accounts for 3.56%of the total area with comparing land use in 2015 and 1980.The area of land use change is small.The SWAT model was used to analyze the impact of land use change on runoff,indicating that the runoff reduction caused by land use change was small.By setting a single land use change scenario and revealing the impact of single land use change on runoff,the analysis shows that the runoff changes in the middle and lower reaches are more sensitive to land use change.?4?The influence factors of runoff change are classified as climate change and human activity.The runoff attribution in huaxian station is the analyzed by the method of reestablish the runoff by SWAT model with modified the relative deviation.The results show that annual runoff from 1971?1993 decreased by 2.878 billion m³ compared with the base period?1960?1970?,among which the contribution rate of runoff reduction caused by climate change is 65.13%.From 1994 to 2016,annual runoff decreased by 5.16 billion m³ compared with the base period,and the contribution rates of climate change and human activities were 43.36% and 56.64% respectively.In order to analyze the annual runoff under the influence of climate change and human activities,the attribution analysis of flood season and non-flood season shows that the influence of human activities on runoff during flood season is stronger than that during non-flood season.