Assessment Of Water Yield And Water Purification Services In Arid Inland River Basins Of Northwest China Under The Background Of Climate And Land Use Change

Water is the source of life and the core element of sustainable development,and provides many essential ecosystem services for ecology,production and life,especially in arid and semi-arid areas.Water is important for the ecological security of the region and human survival.In the arid regions of northwest China,there is little precipitation and large evaporation.In recent years,due to urbanization and the expansion of agricultural,the serious promblems such as river outages,groundwater decline,available water shortage,and eutrophication of lake have affect social and economic development.This paper takes the Bosten Lake basin as the research object from the perspective of ecosystem services,and uses meteorological data,land use,digital elevation,soil and the InVEST model to simulate and evaluate water yield service and water purification service under the background of climate and land use change.Based on the parameter calibration plan of the historical reference period,the paper simulates and evaluates water yield service and water purification service under the RCPs scenario in the future,grasp the spatio-temporal dynamic changes of water yield,nitrogen and phosphorus,and the response of water yield and water purification service to climate and land use change is expected to provide decision support for regional water resources management and sustainable development,as well as new research method for similar regional studies.The main conclusions of this paper are as follows:(1)Precipitation in the Bosten Lake basin has increased over the past 30 years.Under the background of increased greenhouse gases,annual average precipitation in 2020-2050 has increased compared with the historical periods,but the changes will be different in the future periods.The growth rate of precipitation from 1985 to 2015 is 2.61 mm/yr.With the increase of greenhouse gas,the reduction rate of precipitation in 2020-2050 under the RCP2.6 scenario is 0.0361 mm/yr,Under the RCP4.5,RCP6.0 and RCP8.5 scenario,the growth rate of precipitation in 2020-2050 is 0.0017 mm/yr,0.0075 mm/yr,and 0.012 mm/yr respectively.(2)Land use change in the Bosten Lake basin has been dramatic in the past 30 years.Cultivated land and built-up areas have increased rapidly,while forest land,water areas and unused land have decreased significantly.In the context of future climate change,cultivated land and unused land will decrease,and other land use will increase.From 1985 to 2015,cultivated land,grassland,built-up areas increased by 1.66%,11.34%,and 0.25% respectively.Forest land,water areas and unused land decreased by 0.28%,7.04%,and 5.94% respectively.With the increase of greenhouse gas,cultivated land and unused land decreased by 6.7% and 7.24% respectively in 2050,and forest land,grassland,water areas,built-up areas increased by 1.55%,3.33%,0.28% and 0.44% respectively.(3)Under the background of climate and land use change,the water yield service has enhanced,and the water purification service has weakened in the past 30 years of the Bosten Lake basin.From 1985 to 2015,water yield increased by 0.21%,nitrogen and phosphorus retention increased by 41.98% and 40.56% respectively,and nitrogen and phosphorus export increased by 35% and 47.02% respectively.Based on the spatial distribution of water yield,nitrogen and phosphorus retention,nitrogen and phosphorus export in the basin,water yield service and water purification service in the northwest are better than those in the southeast of Bosten Lake basin.Both services are the worst in the northern and western parts of Bosten Lake.(4)With the increase of greenhouse gases concentration,in the context of climate change,the water yield service of the Bosten Lake basin will decrease in 2050 and the water purification service will increase.From the RCP2.6 scenario to the RCP8.5 scenario,the water yield decreased by 8.03%,and the water yield service was reduced,and the water yield service was the best under the RCP6.0 scenario.Although nitrogen and phosphorus retention decreased by 4.32% and 5.38% respectively,nitrogen and phosphorus export decreased by 6.96% and 7.66% respectively,so it can be seen that the water purification service enhanced,and the water purification service is the best under the RCP8.5 scenario.(5)Water yield service in the Bosten Lake basin is affected by climate and land use change.With the passage of time in the historical periods and the future periods,the low precipitation areas decreased and the high precipitation areas increased,and the water yield showed a decrease in low precipitation areas and an increase in high precipitation areas.Water yield change is consistent with land use change.Among them,grassland has the largest contribution to water yield and the strongest water yield capacity.Built-up areas have the smallest contribution to water yield,but the weakest water yield capacity is unused land.With the increase of greenhouse gas concentration,water yield in 2050 under the RCPs scenario will only produce water on cultivated land,forest land,and grassland.Water purification service in the Bosten Lake basin is affected by climate and land use change.The retention and export of nitrogen and phosphorus in the historical periods and the future periods are higher in low precipitation areas and lower in high precipitation areas.As precipitation increases,the retention and export of nitrogen and phosphorus decrease in low precipitation areas and increase in high precipitation areas.Changes in nitrogen and phosphorus retention are consistent with changes in area of cultivated land,forest land,grassland,built-up areas,and are inconsistent with changes in area of water areas and unused land.Changes in nitrogen and phosphorus export are consistent with changes in area of cultivated land,grassland,water areas,built-up areas,unused land,and are inconsistent with changes in area of forest land.No matter in the historical periods or in the future periods,cultivated land has the largest contribution to the retention and export of nitrogen and phosphorus,and forest land and water areas have the smallest contribution to the retention and export of nitrogen and phosphorus;cultivated land,built-up areas have strong retention and export capability of nitrogen and phosphorus,and the water areas has weak retention and export capability of nitrogen and phosphorus.