Recent changes of glacier runoff in the Hexi Inland river basin

Using monthly precipitation and temperature data from national meteorological stations and a digital vector map of modern glaciers from the Chinese Glacier Inventory, the glacier mass balance and glacier runoff in 1961-2006, in the Hexi Inland River Basin (HIRB), China, are estimated based on a monthly degree-day model and compared with the observed data. The results suggest that the modified monthly degree-day model can simulate the long-term changes in glacier mass balance and glacier runoff. It was found that the mean annual glacier mass balance during 1961-2006 was -49.5 mm per year. In the west of HIRB, the glacier exhibited slight negative mass balance; while glaciers in the east experienced serious mass loss. The average annual glacier runoff was 1.02 billion m³ in 1961-2006. Over the entire basin, glacier runoff accounts for 14. 1% of the total river flow. The prominent glacier runoff occurred in the Shule River and Danghe River, which accounts for 31.5% and 41.7% of the river flow, respectively. The results also show that glacier runoff accounts for 22.9% and 5%-15% of the river flow in Beida River and Heihe River, respectively and Shiyang River was less than 10%. Glacier runoff and its influence on river flow have increased in the last 46 years over HIRB.