Assessing the spatial heterogeneity in ecological quality using remote sensing (Case Study: Gharesoo Watershed)

The environment is currently experiencing different changes that are caused by both nature-induced and anthropogenic processes. Land use changes in Gharesoo Watershed noted that there is a necessary need to study ecological quality in this region. In this paper, a remote sensing-based ecological index (RSEI) based on the pressure-state-response (PSR) framework, using the average data of summer images of Landsat satellite in 1989 and 2018 (ETM +/OLI/TIRS sensors), was used to evaluate the changes in ecological quality in Gharasoo watershed of Golestan province. Google Earth Engine (GEE) is used for acquiring and preparing indices, including an indicator of environmental pressure (NDBI), an indicator of environmental state (NDVI) and indicators of local climate changes in response to environmental changes and concerns (LST and LSM). After preparing the indices, the weight of each index was extracted using the principal component analysis (PCA), and then the ecological quality index was created based on the first component of PCA. Analysis of the first component changes using the thresholding method showed a decrease in ecological quality. So that the average RSEI index in 1989 was 0.57 and in 1397 this value reached 0.48, which indicates a decrease in RSEI. Also, the area of very good class in 1989 and 2018 is 32821.83 (16.267%) and 36879.66 (18.27%) hectares, respectively. Spatial variation analysis showed that the poor level of RSEI distributed mostly in the northern areas, and the ecological degradation was  attributed to the fast expansion of the built-up area, characterized by increasing greatly in the value of the normalized differential built up index (NDBI) in such areas.