Remote Sensing Monitoring Of Vegetation Degradation And Ecological Environment In Central Asian Drylands

Recent findings showed that climate changes had caused an unprecedented rate of vegetation degradation in Central Asia over the past 30 years. Socio-economical and institutional changes due to the collapse of Soviet Union also accelerated this decreasing trend. Therefore, we further produced time-series(2000-2013) of grassland coverage based on the pixel dichotomy model using MODIS dataset. Combining with the existing research results of humanity and meteorology, some regions were selected from the study area in the Hotan River Basin, Bosten Lake, Aral Sea and Balkhash River-Ili Lake Basin as typical regions. Based on Landsat images in 1990 s, 2000 s, 2010 s, and 2015, we obtained the land use dataset, vegetation cover dataset, slope dataset and soil erosion dataset of four typical areas. So we extracted the index factors of ecological environmental quality assessment and obtained the weight of each factor using analytic hierarchy process and computed results of evaluation of ecological environment quality by using comprehensive index evaluation method. The main contents and conclusions of this paper were as follows:(1) According to the characteristics of the grassland in Central Asia dryland, we found that pixel dichotomy model can generally retrieve grassland coverage with higher accuracy, comparing four remote sensing retrieval models. We further produced time-series(2000-2013) of grassland coverage based on the pixel dichotomy model and analyzed grassland conditions over Central Asia dryland. Result showed that grassland coverage showed large spatial heterogeneity in the study area. Grassland generally showed degradation trends, especially in the northern and western regions and some basins of Kazakhstan, including the Turgai plateau, Turgay depressions, Kazakhstan hilly north and south of the Ural River Basin, the Caspian Sea, Irtysh River Basin, YBalkhash River-Ili Lake Basin upstream and downstream parts.(2) The grassland, distributed over the typical area of Hotan River basin and Bosten Lake basin, was mainly significantly increase and it was mainly significantly reduced in the typical area of Aral Sea basin and Balkhash River-Ili Lake Basin. The main factor that caused ecological environment changes was increasing area of cultivated land over the typical area of Hotan River basin, Bosten Lake basin, Aral Sea basin and Balkhash River-Ili Lake Basin. The original natural vegetation(grassland, etc.) was replaced, and vegetation structure which trended singleness.(3) The research results were limited in typical areas. In the typical area of Hotan River basin, the condition of ecological environment was relatively excellent. The typical area of Bosten Lake basin, the condition of ecological environment was from relatively good(1990-2000) to relatively excellent(2010-2015). The general situation of the typical area was in the direction of more suitable for human survival. In the typical area of Aral Sea basin, the condition of ecological environment was relatively excellent. In typical area in Balkhash River-Ili Lake Basin, the condition of ecological environment was from relatively general(1994) to relatively good(2000-2014). The general situation of the typical area was in the direction of more suitable for human survival.