Response Of Watershed Runoff To Future Climate And Land Use Change In Karet Area

Land use and climate changes are the main factors influencing the evolution of runoff,and the 6th report of the United Nations Intergovernmental Panel on Climate Change(IPCC)states that this influence will remain into the future;compared to ordinary watersheds,runoff evolution in karst areas is more complex and vulnerable to external environmental changes due to their special karst geomorphology.Therefore,this thesis takes the Chengbi River,a typical karst area watershed,as an example to carry out research on the runoff responses of karst area watersheds under future climate and land use changes.The results are as follows.(1)Based on the 2020 land cover data of the Chengbi River Basin and used the FLUS model to projected for the 2030 s,2060s and 2090 s land use under the SSPs1-2.6,SSPs2-4.5 and SSPs5-8.5 scenarios.The results show that the SSPs1-2.6 scenario has the most erratic development of land use change,with its combined net land use change parameter M increasing from 6.48% to 29.43%;under the SSPs2-4.5 scenario M decreasing from 5.21% to 2.04%;and under the SSPs5-8.5 scenario M decreasing from 6.73% to 0.21%.(2)Based on the Can ESM5 climate model,the ASD model was used to predict daily precipitation and daily maximum/minimum temperatures in the basin from2023 to 2100 under future SSPs1-2.6,SSPs2-4.5 and SSPs5-8.5 scenarios.The results show that the multi-year average surface precipitation for the base period1963 to 2019 was 1341.2 mm,increasing to 1495.8 mm,1496.6 mm and 1534.7mm per annum for the next three scenarios;spatially,compared with the benchmark period,the future average annual precipitation shows the change of decreasing in the upstream region and increasing significantly in the southwest region of the downstream region under the three scenarios.The greatest temporal and spatial variation in mean annual precipitation relative to the base period is observed under the SSPs 5-8.5 scenario,with a decrease of 10.17% upstream and an increase of up to 120.03% downstream.The annual average daily maximum and minimum temperatures for the base period were 27.37°C and 18.51°C,the multi-year average daily maximum and minimum temperature in the future show the phenomenon of heating and cooling.The daily maximum temperature rose to27.54°C and the daily minimum temperature fell to 18.40°C in the SSPs5-8.5 and SSPs1-2.6 scenarios respectively.(3)Based on future land use and climate data,the SWAT model was used to predict the future runoff responses of the basin from 2025 to 2100.From the perspective of annual runoff,the average annual runoff depth for the baseline period 2002 to 2019 was 839.4mm,and the average annual runoff depth shows an increasing trend in the future,especially in the scenario of SSPs5-8.5 shows an increase of 47.5% to 1237.7mm.In terms of monthly runoff,compared with the benchmark period,the average annual runoff depth in the pre-flood season and the main flood season shows a downward trend,and the average annual runoff depth in the post flood season and non flood season shows an increasing trend;especially,under the SSPs5-8.5 scenario,the runoff depth in the main flood season(290.1mm)decreases by 44.80% compared with the benchmark period(525.6mm).In terms of flood and dry runoff,the maximum 1d and maximum 5d runoff depths for the base period were 16.2 mm and 64.9 mm,respectively,and the minimum 1d and minimum 5d runoff depths were 0.1 mm and 0.6 mm.Future annual mean flood runoff depths decrease and dry runoff depths increase,particularly under the SSPs5-8.5 scenario,where the maximum 1d and maximum 5d runoff depths decrease to 11.6 mm and 34.9 mm and the minimum 1d and 5d runoff depths increase to 0.2 mm and 1.0 mm,respectively.(4)The original hydrological patterns have been broken under the influence of climate and land use,and the future development and use of water resources in the Chengbi River basin will need to take these changes fully into account.It is recommended that the staged flood levels of water conservancy facilities be adjusted in a timely manner and that flood monitoring and forecasting be strengthened;that ecological protection zones be established in the basin,that water and soil conservation projects be built and that the rate of urban development in the basin be reasonably controlled.