Study area

The Tuoshigan-Kumalake River plain lies at the northwest edge of the Takelamagan desert, it is characterized by low precipitation (79 mm/year) and high evaporation rates (20 cm pan evaporation 1894 mm/year) (Tang, 2003). Vegetation is distributed mainly along the river main stem and irrigation ditches, and the landscape becomes Gobi where out of the reach of water supply. In this study, the plain boundaries were drawn based on images from the first China Brazil Earth Resources Satellite (CBERS-1) acquired in 2001 with spatial resolution of 20 m by contouring the edge of the oasis, encompassing a land area of roughly 2105 km². Three land use types (vegetation, wasteland, water surface) were determined from the satellitic image. In order to estimate evaporation accurately, the vegetation area was divided into irrigation area and native vegetation. The extent of the irrigation area was determined based on information collected from the local statistics bureau. The irrigation area was further specified to crop types such as wheat, cotton, paddy, and corn according to data from the local statistics bureau. [1]CBERS-1the first China Brazil Earth Resources Satellite

The Xiehela and Shaliguilanke national hydrometric stations mark the northernmost and westernmost limits of the plain. Kaladouwei, the conjunction of the Tuoshigan River and the Kumalake River marks the lowermost limit of the plain. There is no surface water gauge station at Kaladouwei, but the Xidaqiao gauge station is located 15.8 km downstream of the conjunction. In this study, the discharge at the Xidaqiao gauge station is used as a proxy for the discharge at Kaladouwei. Therefore, the separate contributions from the two rivers cannot be distinguished by the observations.