What is the primary factor controlling trend of Glacier No. 1 runoff in the Tianshan Mountains: temperature or precipitation change?

The internal relationship between summer temperature (ST), annual precipitation (AP), annual mass balance (AM) and annual runoff (AR) of Glacier No.1 from 1959 to 2006, a so-called ‘summer accumulation type’ glacier, was examined with several statistical methods including simple linear regression, the Mann–Kendall test and wavelet analysis. In total, ST, AP and AR increase with a rate of 0.02 °/year, 1.53 mm/year and 2.83 × 10 4 m 3 /year, respectively, while AM decreases at a rate of −14.5 mm/year. A step change of ST, AP, AM and AR was identified to have occurred in the mid-1990s. After that, ST and AR increase significantly. Meanwhile, the period of coherence changes from 4–8 years to 2–4 years, implying that when temperature increases greatly, the period tends to be shorter due to the fast response of the glacier. The increase of AR is caused by the loss of AM. The rise of ST is found to be responsible for the loss of AM, although the rise of AP is beneficial to the glacier accumulation. Our results on the dominant effect of temperature (rather than precipitation) on runoff of Glacier No. 1 could be used as the input to models in hydrology, geomorphology, climatology and paleoclimatology.