Evaluation And Prediction Of Ecological Environment Quality In Yanhe River Basin Based On MRSEDI And CA-Markov

The ecological environment serves as the material foundation for human survival and is the fundamental guarantee for social development and progress.A comprehensive,objective,and scientific assessment of the ecological environment’s quality is a prerequisite for achieving harmonious economic and environmental development.As the second largest river in northern Shaanxi,the Yan River not only serves as a crucial source of industrial,drinking,and irrigation water for Yan’an City but also plays a vital role in the overall ecological environment of the northern Shaanxi region.Therefore,conducting monitoring,evaluation,and trend prediction of the ecological environment in the Yan River Basin holds significant theoretical and practical significance.The study utilizes Landsat remote sensing images and other relevant spatial data to develop an improved Remote Sensing Ecological Distance Index(MRSEDI)based on Remote Sensing Ecological Distance Index(RSEDI).Four indicators reflecting the ecological environment characteristics of the Yan River Basin,namely Soil Erosion Index(SEI),Normalized Difference Built-up Index(NDBI),Wetness Index(WI),and Normalized Difference Vegetation Index(NDVI),are selected.The MRSEDI values for the years 2000,2005,2010,2015,and 2020 in the Yan River Basin are calculated.Firstly,the study analyzes the changes in MRSEDI and individual indicators,as well as the correlation between MRSEDI and terrain factors.Then,the CA-Markov model is used to predict and analyze the spatial distribution of MRSEDI levels in the Yan River Basin for the years 2025 and 2030.Finally,based on the land use transfer matrix,the temporal and spatial characteristics of the future ecological environment quality grades in the basin are analyzed.The study establishes an improved MRSEDI model that can be used for rapid comprehensive monitoring and evaluation of ecological environment quality in soil erosion-prone areas.This model aims to provide important references for ecological environment monitoring and protection in the Yan River Basin and northern Shaanxi region.The main conclusions obtained are as follows:(1)The MRSEDI efficiently integrates multiple indicator information and can provide a relatively comprehensive reflection of the ecological environment quality level in the Yan River Basin.It demonstrates good applicability and reliability.By utilizing the Soil Erosion Index(SEI),Normalized Difference Built-up Index(NDBI),Wetness Index(WI),and Normalized Difference Vegetation Index(NDVI)to construct the improved Remote Sensing Ecological Distance Index,it effectively characterizes the ecological environment characteristics of the Yan River Basin,aligning with the basic principles of Remote Sensing Ecological Distance Index(RSEDI).Correlation analysis indicates a significant correlation between MRSEDI and the four indicators,with an average correlation coefficient higher than0.81,indicating a better integration of the information from each indicator.(2)The overall ecological environment quality in the Yan River Basin from 2000 to 2020 showed a gradual improvement trend,but there were significant spatial and temporal differences in the changes of MRSEDI and the mean values of individual indicators.In terms of time,the Soil Erosion Index(SEI)in the Yan River Basin exhibited a slight increase followed by a significant decrease.The Normalized Difference Built-up Index(NDBI)showed a continuous decrease,with a total decrease of 26.98% over the 20-year period.The Wetness Index(WI)displayed a decreasing trend followed by a slight increase,with a growth rate of 7.86%,although the rate of increase was not significant.The Normalized Difference Vegetation Index(NDVI)had a growth rate of57.60%,indicating a general trend of decrease followed by an increase.In terms of space,the high-value areas of SEI gradually decreased,with a tendency of contraction from the entire basin towards the northwest direction.The high-value areas of NDBI showed a contraction trend towards both the northwest and southeast directions in the entire basin,and due to the "mountain removal and urban construction" project carried out in Yan’an City in 2012,the NDBI significantly increased in the central urbanization development area with bare soil.The majority of the Yan River Basin experienced a significant increase in both the Wetness Index(WI)and the Normalized Difference Vegetation Index(NDVI),with only distinct low-value areas remaining in some specific regions in the northwest and southeast parts of the basin.The dynamic changes in the ecological environment quality in the Yan River Basin over the past 20 years were significant.The area with very poor and poor ecological quality ratings continued to decrease,while the area with good and excellent ratings increased.The area with a moderate rating showed a fluctuating increasing trend.From 2000 to 2020,the proportions of areas with ecological environment quality categorized as recovering,stable,and degrading were 55.52%,24.98%,and 19.50%,respectively,indicating an overall improvement in the ecological environment quality of the basin.However,further implementation of localized watershed management measures is still necessary.(3)There is a significant correlation between MRSEDI and terrain factors such as elevation,slope,and aspect.MRSEDI shows an initial increase followed by a decrease with increasing elevation.The average MRSEDI values are higher within the elevation range of 1000-1500 m,and the greatest increase in MRSEDI values occurs within the elevation range of 1100-1200 m.MRSEDI initially increases with slope,but after a slope exceeds 35 degrees,it decreases with further increases in slope.The policy of converting farmland to forests has a noticeable effect on improving the ecological environment quality in areas with gentle slopes or steeper.The ecological environment quality has improved in different slope orientations throughout the entire basin,with more pronounced improvements observed on shaded slopes.(4)Accuracy verification demonstrates that the CA-Markov model is suitable for predicting the spatial pattern of ecological environment quality in the Yan River Basin.The MRSEDI forecast results for2025 and 2030 indicate that the overall ecological environment quality level in the Yan River Basin will improve in the future.The net change rates of the Good,Fair,and Excellent quality levels are positive,while the net change rates of the Very Poor and Poor quality levels are negative.This suggests that the overall ecological environment quality level in the basin will continue to increase.However,challenges such as land degradation in oil,gas,and coal mining areas,surface bareness in urban expansion areas,vegetation degradation in agricultural areas,and soil erosion in hilly and gully regions still persist within the basin.