Variation of baseflows in the headstreams of the Tarim River Basin during 1960–2007

The Tarim River is the largest inland river of China and a major water resource to the vast arid region in northwest China. For its four major headstreams, which contribute 98% of the Tarim River’s streamflow, we investigated the dynamics of baseflow in the past 50 years. The digital filtering method was used to separate baseflow from surface flow, after which the baseflow index (BFI) was calculated and analyzed. The major findings of this study include (1) Baseflows of the four headstreams have increased considerably over the past 50 years. The large baseflow index (BFI) usually occurred in the wet years but the change rate was irregular, because of the increasing recharge from snow and glacial meltwater. (2) The annual baseflow variation of the four headstreams appeared to have cycles of 3–5 years, 10–14 years, and 25 years. (3) The baseflow and BFI showed obvious seasonal variation: The lowest baseflow and BFI typically occurred in December and January, and both increased gradually until the maximums reached in August or July. (4) The responses of runoff and baseflow to climatic factors were different. Precipitation possessed a great impact on runoff, whereas temperature possessed a great impact on baseflow. Baseflow is an important source to the Tarim River, and is affected by the increasing snow and glaciers melt as a result of temperature rise. For the four headstreams, we identified temperature thresholds in the time series of BFI and calculated regression relationships between temperature and BFI in the past 50 years. The thresholds and the regression relationships would help to assess and predict the impact of climate change on headwater inflow to the Tarim River.