Spatiotemporal Response Of Runoff To Climate Change In Yalongjiang River Basin

Climate change and human activities are the two main driving factors affecting hydrological cycle and water resources allocation in the basin.Due to the impact of climate change and human activities,the global hydrological cycle and the distribution of water resources have changed.In the fifth Assessment Report(AR5)issued by the IPCC in 2013,it is pointed out that with the continuous increase of greenhouse gas emissions such as carbon dioxide,the future temperature and radiation forcing will continue to rise,which will have a deeper impact on the hydrological cycle.Yalong River Basin is an important hydropower base in China.In future,the runoff variation of Yalong River Basin will directly affect the operation safety and power generation dispatch of Yalong River cascade reservoirs.Therefore,it is necessary to study the impact of climate change on the runoff of Yalong River Basin.At the same time,because of the gradual change of the climate change process,its influence on the hydrological cycle will be different in different periods;in addition,due to the large latitude span,large altitude change,and great difference in topography and geomorphology in Yalong River Basin,the response of runoff to climate change will also show different characteristics in space.Therefore,further study of spatiotemporal response of runoff to climate change can provide a more specific reference for water resources utilization in the basin.First,the SWAT hydrological model of Yalong River basin is established,and the hydrological model is calibrated by using the historical runoff data of Yajiang,Wali and Xiaodeshi stations.Then,the SDSM downscaling method are employed to predict the daily precipitation,daily maximum temperature and daily minimum temperature of 13 meteorological stations in the Longjiang River Basin in the future 2020-2100,basing on the data outputted by Can ESM2.Then,the monthly runoff of Yajiang,Wali and Xiaodeshi stations in the Yalong River Basin in the future 2020-2010 is predicted.Finally,based on the monthly runoff simulation results,the spatial and temporal characteristics of runoff in Yalong River Basin under three typical concentration paths of RCP 2.6,RCP 4.5 and RCP 8.5 are analyzed,respectively.The main results are as follows:(1)The temperature of Yalong River Basin in the historical period of 1963-2010 shows an overall upward trend,the most obvious upward trend in the middle reaches,the daily minimum temperature rising rate is greater than the daily maximum temperature;the annual precipitation of Yalong River Basin shows an insignificant upward trend in historical period.From 2020 to 2100,the average daily maximum temperature,daily minimum temperature and annual precipitation in the Yalong River basin increased in turn under the three concentration paths of RCP 2.6,RCP 4.5 and RCP 8.5.During the whole forecast period,the average daily maximum temperature and daily minimum temperature in the Yalong River Basin showed an increasing trend in the whole,especially in the upper reaches of the basin.The increase of annual precipitation in the upstream is slightly larger than that in the downstream.(2)In the historical period of 1963-2010,the average runoff of Yajiang station in the upper reaches and Wali station in the middle reaches of Yalong River Basin showed an upward trend,while that of xiaodeshi station in the lower reaches showed a downward trend.The annual average runoff predicted at Yajiang,Maidilong,Wali and Xiaodeshi stations from 2020 to 2100 increases entirely,and the increase amplitude under three concentration paths incline in turn.In terms of annual distribution,first,the absolute increase and the proportion in June are the most significant;second,the runoff of the original main flood season(July-September)except Yajiang Station did not changed significantly,while that of other stations decreased significantly;third,the average monthly runoff has increased significantly in other months(October-May of next year).(3)Under the RCP 2.6 concentration path,the average runoff in the three periods of 2030 S,2050S and 2080 S in Yalong River Basin increased gradually at first and then decreased slightly after reaching the peak value.The average runoff at Yajiang,Maidilong and Xiaodeshi stations all reached the peak value in 2030 S,while that at Wali station reached the peak value in 2050 S.Under the RCP 4.5 concentration path,the overall trend of simulated average runoff increased gradually at first,after reaching the peak value,it tends to be stable,and the monthly runoff of the four stations reaches the peak value in 2050 S.Under the RCP 8.5 concentration path,the average runoff continued to increase.(4)Under the three concentration paths of RCP 2.6,RCP 4.5 and RCP 8.5,the proportion of runoff in flood season to the whole year in Yalong River basin decreases compared with the base period.Under the RCP 2.6 concentration path,the proportion in Yajiang,Maidilong,Wali and Xiaodeshi stations decreases from 73.3%,76.1%,75.5%,77.5% to 68.0%,69.1%,69.6% and 71.2% respectively;under the RCP 4.5 concentration path,the proportion decreases to 67.0%.8%,68.8%,69.4% and 70.9%,respectively,while decreased to 66.1%,67.3%,67.9% and 69.6% respectively,under the RCP 8.5 concentration path.(5)Under the three concentration paths of RCP 2.6,RCP 4.5 and RCP 8.5,the variation trend of the main stream of Yalong River Basin is relatively consistent,while that of the branch shows different variation trends in different concentration paths and different periods.Overall,simulated average runoff of the main stream in the Yalong River basin increased,whereas the increase extent declined gradually from Yajiang Station(upstream)to Xiaodeshi Station(downstream),except for Wali Station.Taking the period of 2030 S under RCP 2.6 concentration path as an example,the simulated average runoff variation proportion in Yalong River Basin decreases from 21.6% at Yajiang Station in the upstream to.4.5% at Xiaodeshi station in the downstream,and the other concentration paths(other periods)show similar tendency.In General,under the condition of future climate change,the runoff of Yalong River Basin will increase as a whole,but it shows different characteristics in different periods(short-term,medium-term and long-term of the 21 st century)and different regions(upstream,middle and downstream of the basin),and with the distribution changes within the year additionally.Therefore,the above changes should be fully considered in the subsequent development and utilization of water resources in Yalong River Basin.