Spatial And Temporal Variation Of Water Yield Ecosystem Service In The Dongjiang River Basin

Humans rely on the ecosystems of the Earth for a variety of functions.Water yield services,as one of the most significant ecosystem services,are critical for sustaining water supply security and ecosystem stability,as well as the long-term growth of socio-economic and ecological systems.The water yield service in watersheds is becoming increasingly unstable as a result of global changes and human activities,and the conflict between regional water supply and demand is worsening as a result of increased human demand for water resources.The study of the spatial and temporal changes in water yield service can help with water resource management and rational consumption,as well as ecosystem management and scientific decision-making in a changing environment.The Dongjiang River Basin is located in the northeastern part of the Pearl River Delta and supplies water to Guangzhou,Shenzhen,Hong Kong,and other cities in the Guangdong-Hong Kong-Macao Greater Bay Area.The demand for water for the national economy in the Dongjiang basin has increased in recent years as a result of population expansion and economic development.Stable water supply and regional water ecological security are important guarantees for regional integration and sustainable socio-economic and environmental development and have received widespread attention from all sectors of society.In this setting,a quantitative assessment of the Dongjiang River basin ecosystem’s water yield service is critical both scientifically and practically.The SWAT hydrological model is established based on regional characteristics to quantitatively assess the water yield of the watershed in this study,which uses the Dongjiang River Basin as the study area.The spatial and temporal characteristics of the basin’s water yield service from 1990 to 2019 were analyzed at different spatial scales.By comparing several scenarios with climate and land use data,the effects of climate change and land use changes on water yield service in the last three decades were investigated.Future climate change and land use scenarios were also utilized to forecast changes in the Dongjiang basin’s water yield service.On this foundation,the current carrying capacity of regional water resources and the supply-demand balance was quantitatively evaluated,and future climate change and land use scenarios were combined to explore the basin’s carrying capacity of water resources and supply-demand balance,as well as to provide reference suggestions for water resource management and protection.The main findings of this paper are as follows.（1）The temperature in the Dongjiang basin showed a fluctuating upward trend from 1990 to 2019,and the results of the M-K mutation test showed that the mean temperature changed abruptly in 2002 and 2012.The annual precipitation didn’t show an obvious trend,and the interannual fluctuation of precipitation showed volatility according to the analysis results of distance level.The main land use types in the Dongjiang basin were forest land,cropland,and construction land.In the last 30 years,the study area had experienced significant urbanization,particularly the downstream of the watershed.The changing trend of land use mainly showed a decrease in the area of cultivated land and forest land and an increase in the area of construction land.（2）The SWAT hydrological model had good applicability in the Dongjiang River basin.The multi-year average water production was 3.64×10¹⁰m3,with large inter-annual variation in water production.The spatial distribution characteristics of water yield service were low in the northeast and high in the southwest.The high-value areas were primarily found downstream of the watershed,such as Shenzhen and Dongguan City,while the low-value areas were primarily found upstream,near Xunwu County and Longchuan County.Sub-basins 39,40,43,and 44downstream of the basin showed higher water yield.（3）It was discovered that climate change had a greater impact on water yield service than land use change,and precipitation was a significant factor affecting water yield in the Dongjiang basin.In the future climate change scenario,the increase in precipitation promoted the increase in regional water yield,and an increase in temperature reduced the regional water yield.When precipitation increases by 10%,water yield in the basin increased by 6.72 billion m³compared to the baseline period,while water yield in the basin drops by 710 million m³when the temperature rose by1°C.The basin water yield increased by 260 million m³in the future land use change scenario compared to the base period,and the water yield of sub-basins 35,39,and 42downstream of the basin improved significantly.（4）The water resources in Dongjiang River Basin were in the balance of supply and demand as a whole.The available water resources could meet the regional water demand with the current annual water resources balance index of 0.47.Spatially localized areas in the southwest of the basin with uneven water supply and demand and limited water carrying capacity,mainly including Huicheng District,Longgang District,and Dongguan City.It was calculated that the total water demand of the study area in 2050 would be 9.53 billion m3,with the Industrial water demand and domestic water demand increasing significantly.The water yield of the basin would increase under the scenario of future climate change,and the water resources balance index was 0.49.The balance index of water resources in the basin was 0.33 under the future land use change scenario,and the water resources carrying capacity of the sub-watershed would be increased in the future.The regional scope of imbalance between supply and demand of water resources will expand,and the bearing pressure of water resources in some sub-watersheds would increase.To promote a rational allocation of water resources and a balance between supply and demand in the Dongjiang River Basin,it would be necessary to develop scientific scheduling and integrated management of water resources in the future.