Effects Of Land Use Landscape Pattern Change On Annual Runoff In The Yihe Basin

This paper takes the above part of Linyi Station in the Yihe Basin as the research area,and based on the annual runoff data measured by Linyi Hydrographic Station from 1975 to 2015,combined with five remote sensing image data(1975,1985,1995,2005,2015).In GIS,FRAGSTATS and other software,the landscape index values of the river basin are calculated.Landscape index analysis was used to analyze the characteristics of land use landscape patterns in the Yihe basin,and the characteristics of annual runoff and annual precipitation in the river basin were analyzed by M-K test method and distance accumulation method.In the SPASS software,the correlation analysis of landscape indicators and runoff indicators at landscape level and type level was carried out to determine the impact of changes in landscape indicators on annual runoff changes in river basins.Therefore,it provides feasible advice for the conservation and ecological management of the water and soil resources in the Yihe Basin.The main conclusions of this study are as follows:(1)The structure and quantity of land use in the Yihe Basin have changed.Cultivated land is the main type of land use in the basin and accounts for more than 60 % of the drainage area.In different research periods,the changes of different types of land use are gradually increasing,indicating that the utilization of land in the Yihe basin is in a period of rapid development.There are frequent changes in the transfer of land types.The arable land mainly flows to construction land and forest land,and the unused land mainly flows to construction land and arable land.(2)Construction land is the most fragmented landscape type in the Yihe Basin.Cultivated land and grassland tend to develop in the direction of fragmentation,and forest land and construction land tend to be centralized.The landscape types with high landscape shape index are grassland and construction land.Forestland and waters are greatly affected by human activities,and the landscape shape index is low and self-similarity is high.The richness and complexity of land use landscape in the Yihe basin are increasing,and the distribution of landscape types in the basin tends to be uniform.Landscape aggregation index and spread index decreased first,and separation index decreased later,indicating that the landscape types of Yihe basin tended to be scattered and concentrated first,especially the concentration of forest land and construction land was the most obvious.(3)The runoff of the Yihe Basin is mainly concentrated in July-September,with an average annual runoff of 1,433 million M,an inter annual extremum ratio of runoff of 62,an annual runoff coefficient of 0.71,and an inter annual variation of runoff.Runoff is extremely unstable.Through the M-K test,it is found that the annual runoff and annual precipitation in the basin show an upward trend.Precipitation is mainly concentrated from June to September.The average annual precipitation is 770.53 mm,the annual extreme ratio of precipitation is 2.76,and the annual variation of precipitation is dramatic.The annual runoff of the basin is greatly affected by the annual precipitation,and the runoff is mainly supplied by precipitation.However,the fluctuation of the annual runoff is much greater than the fluctuation of the annual precipitation.Therefore,the annual runoff of the Yihe basin is affected by precipitation.It is also affected by changes in land use landscape patterns.(4)At the landscape level,the permeability index,aggregation index and runoff depth are negatively correlated,and the separation index,diversity index and evenness index are positively correlated with runoff depth.Throughout the period of study,the diversity index and evennessindex of aroma increased gradually,and the runoff of the basin also showed an upward trend.From the point of view of the specific research period,from 1975 to 1995,the concentration and spread index of the basin gradually decreased,the separation index gradually increased,and the runoff of the basin increased significantly during this period;From 1995 to 2015,the index of watershed concentration and spread gradually increased,the index of separation gradually decreased,and the runoff of the basin decreased during this period,which is roughly in line with the changing characteristics of the annual runoff of the basin.(5)At the type level,the landscape distribution and juxtaposition index,the maximum patch index,and the landscape area ratio of patches are negatively related to the depth of runoff,and the edge density,landscape shape index,and runoff depth are positively related.During the research period,the area of cultivated land is gradually decreasing,and the speed of reduction is faster and faster.The landscape area ratio of cultivated land patches and the maximum plaque index are gradually reduced,and the shape of cultivated land is gradually complicated,which promotes the increase of surface runoff.The landscape area ratio of patches in forest landscape is positively correlated with runoff in Yihe basin,and the landscape shape index and runoff depth are negatively correlated.In recent years,the policy of returning farmland to forests and the construction of large areas of ecological forest gardens have increased the forest land in the basin.Forestland is developing in favor of runoff conservation;There is a positive correlation between grassland landscape separation index and runoff depth,distribution and juxtaposition index,maximum plaque index,landscape area ratio of plaque,and runoff depth,from 1975 to 1995,as grassland continued to open up into arable land,grassland patches gradually became fragmented,the largest plaque index gradually decreased,and grasslands developed in the direction of promoting increased runoff.From 1995 to 2015,The conversion of farmland to forest and grass and the implementation of ecological protection policies have led to the gradual abandonment of arable land into grasslands,and grasslands have gradually become large patches connected by small patches,which has increased the infiltration of runoff and promoted the reduction of runoff.For the landscape of construction land,the landscape area ratio,average patch area,edge density,connectivity,maximum patch index and runoff depth show a positive correlation,and the separation index,distribution and juxtaposition index show a negative correlation with runoff depth.relationship,With the acceleration of the urbanization process,the construction land in the basin is developing toward the trend of centralization.The connection degree,average patch area,and maximum patch index of the construction land are gradually increasing,which reduces runoff consumption and promotes the increase of runoff in the basin.