Abstract: This article aims to explore spatiotemporal patterns in the variation and stability of oases in the Heihe River basin in the last 55 years. This study involved multi-source remote sensing images in 16 periods from 1963 to 2017. Information on the distribution of oases in the Heihe River basin was extracted from the images. Then, the temporal and spatial characteristics of the variation and stability of oases in the basin were analyzed using overlay analysis and a grid-transformed model. According to the transformation from oasis to desert and changes in oasis boundaries, the oases were divided into four categories: stable, expanding, shrinking, and fluctuating. In order to make up for the shortcomings of previous research methods such as single dynamic degree, we established a grid-transformed model of spatial dynamic degree and cumulative dynamic degree considering total change to analyze the spatial distribution of the stability of oases. The results show the following: In the past 55 years, the oases in the Heihe River Basin were predominantly fluctuating. Oasis fluctuations mainly occurred in areas with poor water source reliability and saline-alkaline soil. Expansions of the oasis mainly occurred in the gap between the existing oasis patches in the early years, and occurred on the outer edge of the existing oasis in the middle and later years. Shrinkages of the oasis mainly occurred in the ecologically fragile zone on the edge of the oasis. The expansions of oases in the early years were mainly due to population growth and immigration policies, while the expansion of oases after the year 2000 was mainly caused by the innovation of agricultural production technologies such as drip irrigation and sprinkling irrigation. Oases in the Heihe River basin gradually became stable. The stability of oasis in the lower reaches of the Heihe River was lower than that of oases in the middle of the river. Fluctuations in oases in the middle and lower reaches in Jinta County and Dingxin County mainly occurred in the early stage, while oases in Ejina County fluctuated in the middle stage. Land salinization and broad-shallow and shifting channels of the Heihe River are the important factors influencing oasis stability. This paper constructed a time series of oasis dynamics on the basis of a grid-transformed method. It simultaneously detects the temporal and spatial characteristics of changes in oases and reduces the analysis unit to the grid scale so that changes in oases can be identified and analyzed more effectively.

Key words: oasis, change pattern, stability, remote sensing, GIS, Heihe River Basin