UC Santa Barbara

The authors analyze climatic and hydrologic data from 110 sites collected from the middle of the twentieth century to the present in the Tien Shan, one of the largest mountain systems of central Asia. In spite of a few confounding interregional variations in the temporal changes of surface air temperature, precipitation, runoff, glacier mass, and snow thickness in the Tien Shan, it has been possible to establish statistically significant long-term trends in these key hydroclimatic variables. The average rise in air temperature was 0.01°C yr-1 over the range, with slightly lower values below 2000-m elevation. The precipitation in the Tien Shan increased 1.2 mm yr-1 over the past half-cenutry. The precipitation increase is larger at low altitudes in the northern and western regions than at altitudes above 2000 m. A decrease in snow resources occured almost everywhere in the Tien Shan; the maximum snow thickness and snow duration have decreased on average 10 cm and 9 days, respectively. The annual runoff has dropped or did not change significantly in Tien Shan rivers. The main factor determining the change in river runoff is the type of precipitation (liquid or solid). Over the last few decades, periods of glacier decline have coincided with declining river runoff.