Characteristic Analysis of Baseflow Change and Its Response to Global Change in the Upper Reaches of Heihe River Basin, Northwestern China

The recursive digital filter technique was used to separate annual baseflow of main hydrological stations in the Upper Reaches of Heihe River. The methods of moving average, Mann-Kendall abrupt test and wavelet variance were employed to explain the characteristics of the annual change of baseflow and analyze the reasons of change. The results indicated that the Baseflow Index (BFI) were higher and greater than 0.4 in Qilian, Zhamashike and Yinluoxia stations. The notable increase of baseflow was happened in 1979, when there existed the abrupt point in Qilian and Yinluoxia stations. The baseflow changed fluctuantly in Zhamashike station. The periods of baseflow were 11, 6 and 15 years respectively in Qilian, Zhamashike and Yinluoxia stations. The change of baseflow was mainly affected by precipitation. The increase of air temperature causes the glacier to melt and increase runoff, but the change increased evaporation simultaneously, which made the poor correlation between air temperature and baseflow. The influence of human activities on baseflow was another factor. The forest areas were decreased by human activities, which made the capacity of recharging and adjusting baseflow was decline. In turn, the baseflow went down and more influenced by climatic change. The baseflow change characteristics showed the consistency with the response of northwest China to the global climate change. While the otherness to the global climate change also existed.