Increasing precipitation and baseflow in Aksu River since the 1950s

The Aksu River is the most important recharge source of the Tarim River in northwest China, representing 73.2% of the total volume to the Tarim River in the dry season. There are three types of recharge: glacier-snow melt water, precipitation, and groundwater. Precipitation and baseflow in the basin play a decisive role. The dynamics of precipitation in the last past 50 years were investigated. The digital filtering method was used to separate baseflow from surface flow. Relationships between precipitation and baseflow were identified by correlation analysis and wavelet analysis. The major findings of this study include: 1) In the past 50 years, step changes of both precipitation and baseflow in the drainage basin occurred, and both precipitation and baseflow performed a significant increase trend since the 1960s. The 1990s was the wettest decade of precipitation, and baseflow in the late 1990s was the wettest. 2) The time scale of the annual precipitation time series in the Aksu River Basin are 3, 6, 12, and 27 years, of which the six-year cycle oscillation is the strongest and a main cycle. Aksu River basin annual precipitation is manifested in the smaller time scales, as the time scale increases, the smaller its role is. 3) The baseflow showed an increasing trend in all seasons, and precipitation exhibits a monotonic increasing trend in summer and autumn, and decreasing trend in spring and winter. 4) The responses of baseflow to precipitation were different by season. Precipitation and baseflow have significant common power in the 4–6 year band from 1980 to 1998, and the baseflow has a 0–3 months lag from precipitation.