Quantitatively estimate the components of natural runoff and identify the impacting factors in a snow-fed river basin of China

Snowmelt water is an essential runoff source of some alpine rivers in China. This study selected the Upper Burqin River (UBR), a typical snow-fed river, to quantitatively assess the runoff contributions of different components, as well as the causes of runoff variations under the background of cryosphere change and global warming. Based on the spatial-temporal distributions of snow and glaciers during a year, as well as the altitudinal variations of 0 °C isotherm, the high flow hydrographs in UBR was separated into two parts: seasonal snowmelt flood of lower altitudes (<3,000 m) and glacier-snow melt flow in high altitudes (3,000-4,296 m). The daily baseflow hydrograph of UBR was separated by the digital filtering technique. It is concluded that the contributions of snowmelt flow, glacier melt flow, and baseflow (includes rainfall runoff component) to total annual flow volumes are 27.2% (±2.7%), 8.5% (±1.7%), and 64.3% (±3.0%), respectively. The speed of air temperature rise in spring may be the controlling factor for monthly snowmelt flow distributions in the snow-fed river. The volume of snowmelt was determined by spring precipitation (SP) and previous winter's precipitation (PWP). The PWP changes can explain 43.7% of snowmelt changes during 1981-2010 in UBR, while snowmelt change in 1957-1980 is more impacted by SP. The determining factor of snowmelt variation was changed from SP to PAP during the recent decades. Precipitation in current year, excluding previous year's rainfall and snowfall, can only explain 32%-70% of the variability in total runoff.