Evaluation Of Water Yield And Sediment Retention Ecosystem Services In Nepal Under Different Land Use-climate Scenarios In The Future

Water yield and sediment retention ecosystem services are of great significance for the sustainable development of mountain farming country Nepal.Different climate scenarios and land development strategies may have significant implications on these two ecosystem services.This study uses the FLUS model design plan to simulate three possible land use scenarios in the study area in 2030.Then use the representative concentration path scenarios RCP 4.5 and RCP 8.5 as two possible climate scenarios in 2030.Finally,the above-mentioned data is input into the In VEST model to couple possible climate scenarios and land use scenarios to quantitatively and spatially analyze the water yield and sediment retention of Nepal in 2030.It is expected to provide scientific data support for decision makers to formulate land development policies and ecological protection measures in the future,and realize the sustainable development of regional ecosystems.The conclusions are as follows:(1)The water yield and sediment retention in Nepal under different scenarios in 2030 are both greater than in 2015.Keeping the land use scenario unchanged,from the perspective of climate change,the average water yield and sediment retention of the RCP8.5 climate scenario have increased compared with the RCP 4.5 scenario.Keeping the climate scenario unchanged,from the perspective of land use change,the average water yield and sediment retention under the RCP 4.5 and RCP 8.5 climate scenarios are both in the land use scenario III(ecological conservation scenario)> land use scenario I(natural development scenario)> land use scenario II(economic priority scenario).The RCP 8.5climate scenario + land use scenario III(ecological conservation scenario)can provide the highest Ecosystem Services Status Index(ESSI).This scenario can not only bring the best water yield in the study area,but also increase the amount of sediment retention,and serve the scenario of optimal water yield and sediment retention in the study area.(2)The spatial distribution of water yield and sediment retention in Nepal under different scenarios in 2030 is uneven.The water yield is generally decreasing from southeast to northwest.The areas with higher sediment retention are mainly distributed in the central and northeastern regions.Taken together,the increase rate of Nepal's water yield and sediment retention service area is increasing larger than that of the decreasing rate area.In addition,the hot spots for water yield services are mainly located in the southeast,hot spots for sediment retention services are scattered all over the region.The comprehensive hot spot of soil and water conservation ecological services is located in the northeast of China,where both sediment retention and water yield are higher than their average values.The proportion of integrated ecological service hot spots is shown as RCP8.5 climate scenario + each land use scenario in 2030> 2015 > RCP 4.5 climate scenario +each land use scenario in 2030.(3)The water yield per unit area of major land types in Nepal under different scenarios in 2030 is in the order of construction land> cultivated land> woodland>grassland.The highest proportion of water yield of forest land was always above 44%,while the lowest proportion of water yield of construction land and water body was always below 2%.The sediment retention per unit area of major land types was in the order of woodland> permanent glaciers> grassland.The highest proportion of forest land sediment retention was always over 53%,while the minimum supply of construction land and bare land to Nepal sediment retention was always less than 1%.(4)Climate change factors are the decisive factors of changes in average water yield and soil erosion.To be specific,the contribution rate of climate change factors to average water yield change is between 98.3% and 99.6%,and their contribution rate to the change of average soil erosion is between 97.6% and 99.8%.However,unlike climate change factors,the LULC factors contribute more to changes in soil erosion than to the average water yield.