CLIMATE, SNOW COVER, GLACIERS, AND RUNOFF IN THE TIEN-SHAN, CENTRAL-ASIA

The Tien Shan, a mountainous region located on the northern periphery of central Asia, has a wide range of climatic and hydrological conditi ons. On the basis of long term data from 348 meteorological and glacio logical stations, the annual distribution of precipitation in differen t regions and elevational zones of the Tien Shan was calculated. Major climatic features are the entrance of moisture during spring-summer, small winter precipitation, decrease of precipitation towards the east and the center of the mountains or with distance up valleys, and incr ease of precipitation with altitude up to crest-lines of ranges. Annua l total evaporation from snow can be 50-60 mm per year, reaching 30 pe rcent of snow accumulation. Four main groups of rivers were identified : rivers with mainly snow nourishment, rivers with mainly glacial nour ishment, rivers with mainly rain nourishment, and rivers with mainly g round water nourishment. Coefficient of runoff variation in Tien Shan' s rivers is about 0.20, and coefficient of glacial runoff variation is about 0.15. Glacial runoff is 15-20 percent of the total volume of ri ver runoff.