Study On Ecological Environment Quality Spatio-temporal Evolution And Driving Force In The Upper Reaches Of Zhanghe River Basin

A good ecological environment is very important for the survival and development of human.With the increase of climate change and human activities,regional and global ecological environment problems have become increasingly prominent,weakening the carrying capacity of ecosystem and reduced the quality of human life.The upper reaches of Zhanghe River Basin is an important ecological function area in Shanxi,Hebei and Henan province.But its ecosystem is fragile and local ecological environment problems occur frequently,which brings a great threat to local society and economy sustainable development.Therefore,timely,accurate and comprehensive evaluation of ecological environment quality in the upper reaches of Zhanghe River Basin and in-depth study of its change process and driving mechanism are of great significance for the ecological construction and governance of the region.We mainly used the Landsat surface reflectance data on the Google Earth Engine(GEE)platform and some auxiliary data of meteorology,topography,social economy and land use.Based on remote sensing ecological index,three indicators of normalized mountain vegetation index,slope,and difference index were introduced to construct the advanced remote sensing ecological index(ARSEI)model.Then,we assessed the ecological environment quality of the upper reaches of Zhanghe River Basin in the past26 years,and analyzed its spatio-temporal evolution by using transfer matrix,grid coding and layer analysis.Lastly,combining the natural and human factors,optimal parametersbased Geodetector model was applied to explore the driving force of its change.The main study results showed that:(1)The ARSEI model can better indicate the ecological environment quality of the upper reaches of Zhanghe River Basin.The results of applicability test showed that: The cumulative contribution rate of PC1 and PC2 in various years was greater than 80%,which integrated most information of various indicators.The indicators were divided into two groups of positive and negative effects,and the ecological meaning of PC1 and PC2 was clear.The average correlation between ARSEI and various indicators was the highest,greater than 0.7,and the representativeness of ARSEI was higher than any single indicators.The modeling analysis showed that all of the selected indicators were key indicators,and the indicators that were beneficial and unfavorable to ecology were consistent with the result of principal component analysis.(2)The ecological environment quality of the upper reaches of Zhanghe River Basin had become better,and the average ARSEI increased from 0.411 in 1995 to 0.522 in 2020,with an increase of 27.01%,and the multi-year average ARSEI was 0.483,which was at a middle level.In the past 26 years,the ecological environment quality grade was mainly poor and moderate,and accounting for 65.82% of the total area and the excellent and good grades accounted for 27.22%.The ecological environment quality of different regions varied greatly,showing a spatial pattern of "poor in the southwest and excellent in the northeast".The excellent ecological area was mainly distributed in the mountain region,and the fragile ecological area was mainly distributed in the valley region.(3)The ecological environment quality of the upper reaches of Zhanghe River Basin fluctuated in 58.20% of the region,and continued to improve in 11.21% of the region.The conversion between different grades in various periods was active,mainly by one grade,and change frequency is low,mainly once and twice.The difference in various directions and circles was obvious,with the best in the northeast quadrant 1 to 8 circle and the worst in the southwest quadrant 3 to 6 circle.The spatial clustering of ecological environment quality was significant,mainly high and low clustering.The ecological environment quality of various counties had been improved,especially in Qin County and Tunliu County,with the improvement area accounting for more than 70%.(4)The dominant factors of ecological environment quality in the upper reaches of Zhanghe River Basin were elevation,land use and temperature,and the important factors were precipitation,population density,economic density and slope aspect.The influence of precipitation,economic density and slope direction was increasing,and the influence of elevation,temperature,population density and land use was decreasing.The interaction between various factors was a synergetic enhancement type,including non-linear and two-factor enhancement.Among factor combinations with higher impact,precipitation,elevation,and land use occurred more frequently.65.87% of factor combinations had significant difference in ARSEI.The suitable range of temperature,population density and economic density was Zone 1,precipitation was Zone 8,elevation was Zone 10,and the suitable type of slope direction and land use was sunny slope and forest land.