Changes of landscape pattern bteween 1986 and 2000 in Jiuquan oasis, Heihe River basin

We reported changes of landscape patterns affected by human activities in the Jiuquan oasis, Heihe River basin. Remote sensing products of the Landsat 5 TM in 1986 and the Landsat 7 ETM+ image in 2000 were used to perform the analysis on a digital elevation model (DEM) within a geographic information system (GIS), including patch number, area, shape, and the spatial neighboring characteristics between the oasis patch and the sandy land/Salinized land patches. We found that: (1) the oasis expansion was embodied with an increase in the area of each oasis patch type between 1986 and 2000, while intensive human activities led to an increase in the sandy and barren lands; (2) the desertification threat on farm lands was the most significant in 1986, while the threat on the grasslands was the most severe in 2000. The threats on residential areas were minor both in 1986 and 2000 and remained the same during the 15-year study period, but the threats on other oasis patch types had greatly intensified; and (3) the salinization threats on all oasis patch types decreased in 2000, which was likely a consequence of water diversion effort throughout the region. Clearly, human activities have significantly changed the distribution and allocation of the limited water resources in Heihe River basin, leading to a conflict between the two dominant processes: desertification and oasis expansion. Our results further confirmed the vulnerability and high-dynamic nature of the arid ecosystems.