Identifying The Runoff Variation In The Naryn River Basin In Central Asia Under Multiple Climate And Land-use Changes Scenarios

In recent years,climate change characterized by global warming and land-use change by human activities have continuously caused different degrees of changes in the miscarriage and coalesce process of the hydrological cycles.These changes affecting the availability of water resources and bringing huge challenges to social and economic development and ecological environmental protection.It is a hot spot in water science research to quantitatively distinguish the impact of the two on local hydrological cycle and water resources.In this study,the GCM(Global Climate Model),CA-Markov(Cellular Automata–Markov),SWAT(Soil and Water Assessment Tool)is adopted for simulating hydrological process in Naryn River Basin.The runoff simulation and prediction system explore the process of runoff change under different climate change and land-use change.Specifically,eight GCMs,two representative concentration pathways(RCP4.5 and RCP8.5)and six land-use scenarios(natural development scenario,agricultural development scenario,and ecological protection scenario)are combined to design 96 scenarios.Scenarios reflect the impact of climate change and land-use change on runoff in the Naryn River Basin.Through the calibration and verification,the parameter system of the SWAT model in the Naryn River Basin is constructed.The values of NSE are 0.80 and 0.63,the values of R~2reach 0.80 and 0.64,and the values of Re reach-3.30%and 6.50%in calibration and validation periods,respectively.Based on the constructed model system,forecast the runoff from 2020 to 2099.Analyze the runoff change process at different time scales of year,quarter and month.Reveal the impact mechanism of climate change and land-use change on runoff,and then provide technical support for water resources management in the basin.The main findings of this study are as follows:(1)Analysis of the characteristics of climate change in the Naryn River Basin:From1951 to 1974,the annual precipitation in the basin was 265.88mm,and the increase rate was31.83mm/10a;the annual seasonal precipitation increase rate was summer(13.90mm/10a)>spring(12.06 mm/10a)>winter(3.44 mm/10a)>autumn(0.48 mm/10a).The precipitation series changed abruptly in 1961.The annual average maximum and minimum temperatures were 9.77℃and-5.47℃,respectively.The maximum and minimum temperatures increase rate were 0.61℃/10a and 0.11℃/10a,respectively.The maximum and minimum temperatures series changed abruptly both in 1960.The future average annual precipitation and temperature would show continuous growth.By the end of the 21st century,the average precipitation under all GCMs would be 39.3%(RCP4.5)and 44.3%(RCP8.5)higher than the base period;the maximum temperature would be[0.11,0.57]°C/10a rate increases to[10.35,15.69]℃;the lowest temperature increases[-1.79,3.26]℃by[0.10,0.56]°C/10a.(2)Analysis of the characteristics of land-use change in the Naryn River Basin:The land-use in the Naryn River Basin is dominated by grassland.Human economic development mainly affected the change of agriculture land,accounting for 3.92%in 2010.The land-use map in the Naryn River Basin in 2010 obtained by the CA-Markov model is relatively close to the actual situation(the fitting degree is 0.80).The prediction results show that by 2080s,under the natural development scenario,the agriculture land would become 6.16%,under the agricultural development scenario,it would change to 11.11%-32.07%,and under the ecological protection scenario,it would change to 2.87%-3.46%.(4)The impact of future climate and land-use changes on runoff:Climate change increases the annual surface runoff,which shows an increasing trend in spring,summer and autumn,and a decreasing trend in winter.Land-use change increases water supply while increasing water consumption.For every additional hectare of agriculture land,an average of2.6×10~3m~3of water shortage would increase,which means that the expansion of agriculture land should be cautious in the future.Under the combined change of climate and land-use,the future runoff would change in the range of 410.63m~3/s to 649.82m~3/s.Compared with the two scenarios of ecological protection and natural development,the annual average runoff of the agricultural development scenario is significantly higher.Climate change plays a leading role in runoff variation.Summer is the most sensitive to climate and land-use changes.The future peak runoff would be at least 20.08%higher than the base period,and the valley runoff would be at least 26.28%lower than the base period.