Analysis of landscape change drivers in the Ejina natural oasis
额济纳天然绿洲景观演化驱动因子分析

The Ejina natural oasis landscape lies in the lower reaches of the Heihe river basin in the arid inland regions of northwestern China. With decreasing water resources from the upper reaches of the Heihe river basin, many urgent ecological and environmental issues in the Ejina natural oasis have become more pressing in recent years. Using remote sensing techniques and GIS, based on Landsat Thematic Mapper data in 1987 and 1994 and Landsat Enhanced Thematic Mapper Plus data in 2001, the changing patterns of the Ejina natural oasis landscape showed that: (1) During the past 15 years, the water area and main oasis area sharply decreased. The oasis desertification process is more serious at present than before. (2) The most intense conversion among different landscape types was occurring in the transitional zone between oasis landscapes and desert landscapes. (3) As results of the Ejina natural oasis landscape change, the landscape patch complexity and heterogeneity were significantly reduced. Moreover, the landscape texture became increasing coarse and the landscape diversity and stability were decreased. Based on the general characteristics of the Ejina natural oasis landscape during the past decade, some key driving factors, including climate change indicators, hydrological indicators and human activities indicators, were analyzed. The climate change indicators consisted of evaporation degree, wetness coefficient and dryness degree, which were calculated from the meteorologic data of precipitation, air temperature, evaporation and humidity from 1957 to 2001. The hydrological indicators were the annual change of surface water quantity from 1947 to 2001, the spatio-temporal change of groundwater level between 1980s and 2000s, and the change of groundwater quality in recent years. The human activities indicators were changes in total population, livestock quantity and farmland area in the past 50 years. Results show that: (1) Increased evaporation degree, decreased wetness coefficient and enhanced dryness degree in the past decade, especially in recent years, all accelerated the desertification of the Ejina natural oasis landscape; (2) Significantly reduced surface water quantity from the upper reaches of the Heihe river basin, which simultaneously led to descending groundwater level, ascending groundwater mineralization degree and soil saltness content, and badly deteriorating water quality, was the key driver for the degradation of the Ejina natural oasis landscape; and (3) Increased intensity of human activities induced by rising population and livestock in recent decades, overgrazing livestock in the fragile natural oasis regions, and frequently reclaiming and abandoning farmland owing to unbalanced distribution of limited water resources were also important driving factors for the Ejina natural oasis landscape degradation in past decades. Furthermore, owing to the ecological fragilities and the difficulties of ecological restoration for the natur