Precipitation and urban expansion caused jointly the spatiotemporal dislocation between supply and demand of water provision service.

A clear quantification and spatial mapping between supply and demand of water provision service in relation to climate change and urban expansion can provide some guidance to water resources management. Nevertheless, so far, most researches ignored the dynamic changes and influences of supply-demand coupling correlations. In this study, water yield and water demand were quantified and mapped in the Xiangjiang River Basin (XRB) from 2000 to 2018 by using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) and water-demand models, then the spatial distribution characteristics and their matching relationship were identified by using the univariate local autocorrelation analysis and the common logarithm of water supply-demand ratio (WSDR). With that, the contributions of climate and socio-economic factors to the above-mentioned changes were explored by using geographic detector. Results showed that the annual water yield increased by 20.20% in 2000-2015 and decreased by 33.92% in 2015-2018 affected by precipitation and land use changes; Changsha-Zhuzhou- Xiangtan urban agglomeration (CZX) and Southwest of Yongzhou were the high value areas of water yield (>338 m3/hm2). Due to the urban expansion, the water demand increased by 40.50% from 2000 to 2005 and decreased by 36.39% after 2005; From 2000 to 2018, high value areas of water demand (>53566 m3/hm2) mainly appeared in midstream and downstream with high urbanization level, dense population and developed industry. Under the joint action of precipitation (prep) and urban expansion, the overall state of supply and demand in the upper reaches was surplus, and more than 90% of the regions in midstream and downstream were at the middle and high level of supply shortage, especially in Hengyang and Chenzhou. Consequently, the increasing needs of human beings should be emphasized from the overall perspective of the basin, the growth rate of construction land and the necessary green infrastructure should be controlled reasonably and configured for achieving win-win goals of coordinating environmental protection and urban development.

Spatiotemporal dislocation of urbanization and ecological construction increased the ecosystem service supply and demand imbalance.

The spatiotemporal dislocation of urbanization and ecological construction may lead to differences in the spatiotemporal pattern and matching of the ecosystem service supply and demand, which are significantly important in altering the ecosystem service supply and demand equilibrium. This study quantified and mapped the supply and demand of carbon sequestration services in the Xiangjiang River Basin (XRB) from 1990 to 2015 using the InVEST and population distribution models and identified the spatial distribution characteristics and changes in the supply and demand relationship on the sub-basin scale using the spatial autocorrelation method and Z-scores. The results show that the expansion of land urbanization greater than 50% was concentrated in the midstream and downstream, while the ecological construction was mainly distributed in the upstream. On the whole-basin scale, the supply of carbon sequestration services slightly decreased by 21.62%, while the demand sharply increased by 376.86%. The carbon sequestration services supply-demand ratio (CSDR) reduced from 0.16 (1990) to -0.03 (2015). This meant that the status of the supply and demand in the XRB had changed from oversupply to overdemand, and this tide turned in 2005 (-0.01). Furthermore, the spatial distribution pattern of the sub-basins' CSDR in the upstream was the High-High cluster, while it was the Low-Low cluster in the downstream. These results revealed the high spatial distribution consistency between the CSDR and urbanization and ecological construction. The slight increase in the carbon sinks caused by the ecological construction in the upstream could not offset the rapidly increased carbon emissions from the downstream for urbanization. Meanwhile, the lack of ecological concern during the urbanization process had led to a persistent reduction in the carbon sinks in the downstream, which also exacerbated the disequilibrium of the ecosystem service supply and demand in the XRB. Consequently, this study suggests that the scale and speed of the urbanization of land should be reasonably controlled and that the ecological construction in rapid urbanization regions should be strengthened to meet the demand for ecosystem services.