Abstract: There is evidence of significant climate changes over the past decades in northwest China. Studies are needed to characterize changes in climate variables over space and time. In this study, we collected daily data of air temperature and precipitation for the period of 1960-2009 along the Kaidu River which is located at the south of the Tianshan Mountains in Xinjiang, northwest China. Four meteorological stations were included, i.e., the Bayinbuluke Station at the upstream, and the Yanqi Station, Hejing Station, and Heshuo Station at the downstream. For the downstream, we used averaged values from the available three stations. The statistical analyses (e.g., trend analysis and anomaly) were applied to compare the temporal variability of temperature and precipitation between the upstream and downstream, focusing on seasonal, interannual and interdecadal variations. Our analyses indicated that there were significantly increasing trends in the annual mean temperature and the annual minimum temperature over the past 50 years. In general, there was a good correlation between the annual minimum temperature and mean temperature in this region. While annual mean temperature showed a similar increasing trend (i.e., 0.27 ℃/10 a at the upstream and 0.22 ℃/10 a at the downstream), the annual minimum temperature revealed a greater increasing trend at the downstream (0.61 ℃/10 a) than at the upstream (0.41 ℃/10 a). On average, the annual mean temperature over the most recent decade was 0.97 ℃ higher at the upstream and 0.69 ℃ higher at the downstream relative to those averaged over the past 50 years. Further analyses demonstrated that there were pronounced changes in temperature during the season of November – March at decadal time scale. In particular, the largest positive temperature anomalies in winter were found during the most recent decade at the upstream, and during the period of 1990-2009 at the downstream. Overall, there was a decreasing trend in the seasonality of temperature along the Kaidu River, despite of a considerable fluctuation at the upstream. Annual precipitation was higher at the upstream (273 mm) than at the downstream (77 mm), with majority during summer. There was an increasing trend in the annual precipitation, i.e., 9.13 mm/10 a (P< 0.05) at the upstream and 5.34 mm/10 a ([WTBX]P[WTBZ]= 0.07) at the downstream. In addition, there was a modest fluctuation in precipitation at seasonal to decadal time scales. The changes in temperature and precipitation over the past 50 years would have implications for the water cycle in this region.

Key words: Kaidu River, climate change, temperature, precipitation