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Impact of Climate Change on the Alpine Streamflow During the Past 40 a in the Middle Part of the Qilian Mountains, Northwestern China

DING Yong-jian, YE Bai-sheng, LIU Shi-yin (Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000. China)  
Visible climate change in the interior catchment of arid northwest China during the past 40 years occurred. By analyzing the climate change in the Heihe River and the Taolaihe River catchments of the Qilian Mountains. the characteristics of climate change, the relation between climatic elements and annual streamflow in the catchments were discussed in this paper. Changes in alpine precipitation and temperature were seasonally different in the past 40 years. Precipitation in summer and winter appeared to increase and that in spring and autumn tended to decrease. Annual precipitation presented totally an increasing tendency. Temperature in autumn and winter tended to increase, especially in winter. Spring temperature decreased slightly and summer temperature was relatively steady. Annual temperature showed a slow increasing tendency. Summer precipitation increased 14.84 mm per decade though its change rate was much less than that of winter precipitation, that increased with a speed of 1.2% per year. The rising of winter temperature rate, 0.352 K per ten years, was marked. Though seasonal precipitation and temperature varied by a way of some increase and some decrease in the Qilian Mountains in the past 40 years, annual precipitation and temperature tended to increase as a whole. The streamflow in each season appeared to be an increasing tendency, with higher rate in spring and summer. Especially, spring streamflow appeared to have the highest increasing rate, 0.267 × 108 m3 per decade, equivalent to an increasing spring streamflow volume of 1.2% per year. The marked increase in spring streamflow was probably associated with increasing winter precipitation. Influence of spring precipitation on streamflow closely related to spring temperature. Increasing summer streamflow directly associated to summer precipitation. However, increasing rate of summer streamflow was less than that of summer precipitation in comparison to the change of seasonal streamflow and precipitation, which most likely related to a decrease of spring precipitation, resulting in a reduce of snow cover and an influence on the supplement to summer streamflow. Models of response of the streamflow to climate change for the Heihe River and the Taolaihe River were set up. It is revealed that most important factor influencing streamflow in the Heihe River is precipita- tion. Increasing precipitation made annual flow increase to 16% as compared with the average annual flow, but rising temperature made annual flow reduce to 3.6%. Average increase of streamflow is about 12.4%, equivalent to a water amount of 1 .9 × 108 m3. Climatic effect on streamflow in the Taolaihe River is complicated. The tendency of streamflow change in the Taolaihe River is decreasing. opposite to that in the Heihe River. An important cause on decreasing streamflow is rising temperature. Reducing streamflow by rising temperature is 10.4% of the average. Though rising temperature in spring and summer resulted in positive contribution to streamflow due to the increase of snowmelt, glacier ablation and annual precipitation. the forceful negative effect of rising temperature on streamflow is not able to eliminate. The results calculated from the two selected alpine adjacent catchments indicate that under varied hydrological conditions and different tendencies of seasonal climate change, dissimilar change tendency in streamflow will appear: increase in the Heihe River and decrease in the Taolaihe River.
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