Analysis on the Effects of Climate Change on Natural Runoff Volume in the Upper Reaches of the Yellow River

The catchment area of upper reaches of the Yellow River upstream from Lanzhou is 2.225 5×105 km2, which occupies 28% of the total area of the Yellow River Watershed. The average annual natural runoff volume of the Yellow River at Lanzhou Hydrological Station was 3.32×1010 m3 during the period from 1959 to 2002, which occupied 60% of the total annual runoff volume of the river, so the upper reaches are the main areas of runoff formation and water conservation in the Yellow River Watershed. In this paper, the climate change characteristics in the upper reaches of the Yellow River in recent 44 years are analyzed using the data of monthly temperature and precipitation during the period from 1959 to 2002. The correlation coefficients between the annual air temperature and precipitation at each meteorological station upstream from Lanzhou and the annual natural runoff volume at Lanzhou Hydrological Station are calculated. After selecting the representative stations and the typical periods of time, the equation of calculating the natural runoff volume is developed, and the sensitivity of natural runoff volume to the climate change and the effects of climate change on the runoff volume are analyzed. The results are as follows: (1) Annual runoff volume of the Yellow River is increased with the increase of precipitation but decreased with the increase of temperature; (2) The response of the annual runoff volume to precipitation change is more significant than that to temperature change; (3) The effect of climate change on annual natural runoff volume has been significant since the 1990s, and the affecting scope is 13.2%.