Dynamic Monitoring And Evaluation Of Eco-environment In The Earthquake-stricken Area Of Wenchuan Earthquake In The Past Ten Years Based On Remote Sensing Technology

The mountainous areas in southwestern China are the main sources of the Minjiang River,Dadu River,Tuojiang River,and Fujiang River.They are an important part of the ecological security barrier in the upper reaches of the Yangtze River,and they have important ecological service functions about water source conservation and soil and water conservation.The area is located in the Mediterranean-Himalaya earthquake zone,which is the transitional area from the southeastern edge of the Qinghai-Tibet Plateau to the Sichuan Basin.It has developed multiple fault zones,and has become one of the most significant and violent seismic activity areas in China.Over the past ten years,there have been many large earthquakes with Ms7.0 or above in the region.Among them,the Wenchuan Yingxiu Ms8.0 earthquake occurred on May 12,2008.Secondary disasters such as landslides,collapses,debris flows,and dammed lakes caused by the earthquake have had a major impact on the regional ecological environment.The destruction of vegetation,the loss of habitats of endangered organisms,the damage of species diversity,the intensification of soil erosion in the mountains,and the degradation of water conservation functions have made the regional ecological environmental protection and economic development increasingly prominent.Regional ecological and environmental problems are increasingly prominent.With the development of the ecological reconstruction in the Wenchuan earthquake-stricken area,the ecological environment in the area has gradually recovered.Although there have been some research results in the Wenchuan earthquake-stricken area,based on the “3S” technology,the use of remote sensing data to monitor and evaluate the ecological environment in the ten years after the earthquake-stricken area is still relatively lacking.For this purpose,Maoxian County was used as a research example area to carry out extraction and analysis of remote sensing information parameters of the ecological environment in the severely affected areas of the Wenchuan earthquake and quantitative research on the temporal and spatial dynamic changes of the ecological environment before and after the earthquake.In this study,"3S" technology is used to retrieve regional ecological environment remote sensing information,and to mine ecological information of remote sensing data.Based on AHP,entropy weight method and minimum relative information entropy theory,comprehensive evaluation of the ecological environment before and after regional earthquakes is conducted.This study have grasped the characteristics of the spatio-temporal dynamics of the ecological environment before and after the earthquake in the Wenchuan earthquake-stricken area.And ecological restoration suggestions are put forward.Based on the above conclusion,this study provide reference and technical support for regional post-disaster reconstruction,natural resource management and protection.The main results achieved in this study are as follows:(1)Landsat images are used.Based on remote sensing images,support vector machine classification method is used to extract the land use information and build land use comprehensive degree index by establishing grid in the study area.Based on the normalized vegetation index,the vegetation coverage in the study area is estimated.Using the thermal infrared band of the Landsat images,the atmospheric correction method is used to extract the surface temperature distribution Remote sensing data,meteorological data,soil data,and digital elevation model to extract rainfall erosion force,vegetation coverage factor,soil erodibility,terrain relief,and gully density is used to establish a soil erosion model.(2)Based on the extraction results of ecological environment remote sensing information parameters,it can be seen that in terms of land use,the area of forest land and water area in the study area decreased the most in 2008.In 2013,the area of unused land decreased,the area of construction land increased sharply,and the area of cultivated land decreased slightly.In 2018,unused land continued to decrease,the growth rate of construction land area moderated,and the cultivated land area increased.The comprehensive degree of land use first decreased and then increased.In terms of vegetation coverage,the area with high vegetation and extremely high coverage flows to areas with lower coverage.In 2013,the area of extremely high vegetation coverage increased significantly.In 2018,the area of extremely high vegetation coverage further increased.In terms of surface temperature,the soil under the regional vegetation is exposed under the influence of the earthquake.Exposed land absorbs more heat,and the temperature moves towards higher temperatures.In 2013,the surface temperature of the dry valley continued to rise,inhibiting vegetation restoration.In 2018,the regional vegetation coverage increased,and the high temperature range declined.In terms of soil erosion,the soil erosion in the study area is mainly lightly sensitive,and the proportion of severely and extremely sensitive is the smallest.(3)Based on the analytic hierarchy process,entropy weight method and minimum relative information entropy,8 natural condition factors such as surface temperature,vegetation coverage,elevation,terrain relief,soil erosion sensitivity,biological abundance index,gully density and average annual rainfall,and 2 persons including land use degree and population density are selected to establish an ecological environment comprehensive index evaluation model.The results show that the average value of the eco-environmental index fell in 2008 compared with before the earthquake.In 2013,it increased.In 2018,it continued to rise.During the study period,the ecological environment of the study area was mainly excellent and good grades,and the poor grade areas were mainly distributed in the central Wadi Township-Weimen Township and the southern Fengyi Town-Nanxin Town Valley.At the same time,according to the temporal and spatial changes of the ecological environment,suggestions were put forward for the restoration of the ecological environment in areas with good ecological environment,general ecological environment,and poor ecological environment.