The Impact of Land Cover and Land Use Changes on the Hydrological Cycle of the Tarim Basin, NW China

Abstract:

The Tarim Basin, located in NW China, is the largest inland basin in the world. Since 1970s, the basin became modernized agriculturally through unprecedented reclamation which were controlled by the Chinese government to promote cotton production. In 2013, 40% of China’s cotton production is harvested in the Tarim Basin, representing 15% of world production. However, these large scale land use transformations lead to overuse of water resources in the upper and middle reaches for irrigation, with severe unintended ecological consequences in the lower reaches. The lower reaches of the Tarim River dried up gradually during the 1970s. In 2000, a water release project was launched to meet the ecological water demands of the river’s lower reaches. So far there have been 15 water releases with 1.7 billion USD invested.

This work aims to improve our understanding of the impacts on the hydrologic cycle from land-use/land-cover change activities in the Tarim Basin by bridging boundaries between different disciplines and integrating them to portray all the key processes involved. This multidisciplinary approach includes analysis of remotely sensed imagery, application of a dynamic crop modelling framework, and simulation analyses with a transient, 2D, variably-saturated groundwater model. My primary findings show that in 2006, about 25820 km² were identified as irrigated field. This is a 41% increase from 1970s, when the total irrigated area was only 18250 km². The rapid expansions in irrigate fields, together with climate change, have affected the partitioning of water between the land surface and the lower atmosphere through changing evapotranspiration patterns. Approximately 7 km³ of water entered the atmosphere through crop evapotranspiration in 1971, but by 2006 this value had increased to nearly 11 km³. But changes in climatic conditions accounted for only 20% of the total increase in ET. In terms of ecological restoration, the study shows the current water releases project can maintain the current habit for Populus euphratica, but are not sufficient to expand habitat for Populus euphratica. This research addresses the hydrological and ecological implications of agricultural expansion and identifies sustainable strategies to reverse these negative environmental effects in the Tarim Basin.