Spatio-temporal changes of water resources ecosystem services in the Hanjiang River Basin based on the shared socioeconomic pathway

A comprehensive assessment framework for watershed ecosystem services and trade-offs was proposed for watershed governance and regional sustainable development in this paper. The framework integrated both shared socioeconomic pathways (SSPs) and future land use simulation (FLUS) models. The socioeconomic data of China’s provincial SSPs considering domestic development and regional differences were introduced to the FLUS model, meeting the needs of regional level land-use simulation scenarios and fully considering the interaction between human socio-economic activities and the natural environment. Taking the Hanjiang River Basin as an example, the FLUS models under different SSPs scenarios were built to evaluate the ecological and environmental effects on land-use change. We further investigated the response of water conservation and water quality purification services to social development decision-making and spatiotemporal evolution by using InVEST model. Results showed that: 1) the water production depth in 2035 under all the SSP scenarios was significantly higher than that in 2015. The increment under the SSP1 and SSP2 scenarios was relatively small, and the increment under the SSP3 scenario was relatively higher with the most intense change. The areas with increased water production depth were mainly concentrated in the southeast, central, and western regions of the Hanjiang River Basin. 2) From 2015 to 2035, due to frequent human activities and rapid urban expansion, in areas where the water production depth increased, urbanized land also increased significantly. According to the land-use simulation and water production depth change results, urbanized land had a strong water production capacity due to low vegetation coverage, weak evapotranspiration, and low permeability of hardened ground. 3) The nitrogen and phosphorus loads in the SSPs scenarios in 2035 were lower than those in 2015. The reduction under the SSP1 and SSP5 scenarios was relatively large, and the SSP3 scenario was the same as that in 2015, but the change was the most intense. The areas with increased nitrogen and phosphorus loads were mainly concentrated in the southeast and western regions. 4) According to the results of land-use simulation and nitrogen and phosphorus load change, the urbanized land had more pollutants due to the frequent human socio-economic activities, while the cropland was due to the use of chemical fertilizers and pesticides in the process of agricultural production, making part of the nitrogen and phosphorus elements not absorbed by crops. The two types of land-use caused serious pollution in the water environment of the basin. The future development planning of the Hanjiang River Basin can be based on the SSP1 scenario, referring to the economic and technological development model under the SSP5 scenario, combined with the basin functional district, optimizing the land-use structure, and ensuring the water ecological environment security of the basin while paying attention to economic development. The results of this study can be used to prepare territorial spatial planning and sustainable water resource asset management in the Hanjiang River Basin, support the construction of the Hanjiang River eco-economic belt, and promote the improvement of the water ecological environment in the Yangtze River Basin.