Response of ecological environment quality to land use transition based on dryland oasis ecological index (DOEI) in dryland: A case study of oasis concentration area in Middle Heihe River, China

Oasis ecosystems in dryland regions take on crucial significance in human survival and development since the quality of these regions that are characterized by ecological environments directly affects the well-being and socio-economic progress of their residents. Accordingly, it is of utmost importance to evaluate changes in ecological environment quality (EEQ) and gain insights into how land use transformation affects the local ecological condition, thus guiding the sustainable development of the dryland oasis. In this study, we evaluated the EEQ of the Middle Heihe River (MHR) from 1985 to 2020 by constructing the dryland oasis ecological index (DOEI) through the Google Earth Engine (GEE) platform. Moreover, we investigated how land use transformation influenced the EEQ of the MHR. Results suggested that (1) the DOEI can effectively capture the comprehensive dynamics of long-term EEQ changes in MHR, providing a more accurate representation of land type characteristics. (2) The EEQ in MHR generally exhibited a trend of initial improvement, followed by deterioration. The desert-oasis transition zone acts as the most significant area of EEQ changes in the MHR. The mutual transformation among cropland, grassland and desert is the primary factor for EEQ in the MHR. (3) The expansion of cropland in the MHR pronouncedly affected the EEQ. However, this continuous expansion may impose greater stress on water resources while potentially threatening ecological degradation in the lower reaches of the river basin. The DOEI built through the GEE platform is capable of indicating the spatiotemporal status of the EEQ in the dryland oasis, which holds significant implications for studying the interaction between human activities and EEQ in the dryland oasis.