Impact of climate on runoff in the source regions of the Yellow river

Runoff regeneration processes are one of the key processes in the water cycles. Runoff can be separated into direct runoff and baseflow according to the response rate to precipitation.The baseflow is generally defined as the part of river runoff come from groundwater storage and other delayed water, while the direct runoff is defined as the part of river runoff direct response to precipitation. Based on this theory, the impact of climate factors on runoff is analyzed by investigating the conversion rate of precipitation to total runoff, baseflow and direct runoff. In the sources regions of the Yellow river, runoff coefficient was in positive relation with precipitation and in negative relation with air temperature; runoff increased with the precipitation. In the 1990s the sharp decrease of precipitation and increase of temperature contributed to the decrease of runoff. Impacts of climate on runoff were different in different subbasin in the source regions of the Yellow river. In subbasins above Jimai hydrologic station with mean annual temperature below -3.0 ℃, temperature was the key factors affecting runoff. With the increase of temperature runoff will decrease. In subbasin between Jimai hydrologic station and Maqu, runoff and baseflow both increased with the increase of precipitation, and decreased with the increase of temperature. In subbasin between Maqu and Tangnaihai hydrologic stations, precipitation was the vital climate factor affecting runoff(including baseflow and direct flow and total runoff), only direct flow are slightly influenced by temperature.