CLIMATIC AND HYDROLOGIC CHANGES IN THE TIEN-SHAN, CENTRAL-ASIA

The authors analyze climatic and hydrologic data from 110 sites collec ted from the middle of the twentieth century to the present in the Tie n 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 s now thickness in the Tien Shan, it has been possible to establish stat istically significant longterm trends in these key hydroclimatic varia bles. The average rise in air temperature was 0.01 degrees C yr(-1) ov er the range, with slightly lower values below 2000-melevation. The pr ecipitation in the Tien Shan increased 1.2 mm yr(-1) over the past hal f-century. The precipitation increase is larger at low altitudes in th e northern and western regions than at altitudes above 2000 m. A decre ase in snow resources occurred 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 so lid). Over the last few decades, periods of glacier decline have coinc ided with declining river runoff.