Changing runoff due to temperature and precipitation variations in the dammed Jinsha River

Impacts of climatic variations and human activities on water discharge in the lower streams of dammed rivers have been widely studied due to the rich water resources and hydropower potential. However, the effects of climate variations in upper streams on the whole river system are always ignored. Therefore, integrated methods of hydrological modelling and numerical analysis were employed to identify runoff characteristics in response to climatic variations in conjunction with hydroelectric exploitation in the Jinsha River in the "Asian Water Tower" region. While there was no significant rise in annual precipitation for most areas from 1970 to 2017, highly significant upward trends in temperature were observed in areas along the mainstream. Snowmelt periods varied between upper and middle streams due to constantly varying geographic conditions. Peaking runoff of 56.67 m(3) s(-1), 1350.12 m(3) s(-1), 175.63 m(3) s(-1), 2343.89 m(3) s(-1), 1855.02 m(3) s(-1), 3285.61 m(3) s(-1), and 10,922.65 m(3) s(-1) occurred during July in Tuotuohe, Qingshuihe_Jinsha, Qingshuihe_Yalong, Batang, Kangding, Xianggelila, and Yibin, respectively, along the Jinsha River. During snowmelt periods, runoff in the upper stream was greatly influenced by temperature changes. However, during recent periods, runoff in the middle stream has also become sensitive to rising temperatures, as indicated by change points. The contribution of runoff from upper streams to the outlet increased from 10.57% (naturalised river period) to 13.01% (individual reservoir period), followed by a further increase of 13.37% (cascade reservoirs period). Seasonal differences were observed up to the middle streams, where more runoff occurred at the outlet during flood seasons due to hydroelectric exploitation after 1999. Annually, runoff contribution in different areas increased in response to climatic variations during 1999-2017. This study highlights the vulnerability of runoff variations in upper streams to climate change. Watershed management rather than river regulation alone is needed, which could help water resources management for the entire river system.