Characteristics of urban expansion in megacities and its impact on water-related ecosystem services: A comparative study of Chengdu and Wuhan, China.

[Display omitted] • A comparative study of urban expansion and WESs in two megacities was conducted. • In Chengdu, urban expansion had an edge-based pattern that encompassed city-wide. • In Wuhan, suburban expansion is growing rapidly due to leapfrogging development. • Urban expansion has larger negative effects on WY and WP in Wuhan's suburbs. • Ecological land in the megacities' center suffered from indirect loss of WESs. The megacity expansion that continues to occur in developing countries is an unavoidable trend at this stage, yet there exists a dearth of knowledge regarding the comprehensive impacts of urban expansion on water-related ecosystem services (WESs) within these areas. Taking Chengdu and Wuhan, two megacities in the upper and middle Yangtze River Economic Belt in China as the study area, this study first compare the magnitude, rate, spatial divergence, and the mode of urban expansion; then evaluate its impact on three typical types of WESs, i.e., water yield (WY), water purification (WP), and habitat quality (HQ) using spatial econometric models and bivariate Moran's I. The research findings show that Chengdu's suburbs tend to experience edge-based expansion along rivers, while Wuhan's city center also spreads outward in edge-based from the river junctions of the Yangtze and Han rivers. Urban expansion negatively impacts all three types of WESs, and its effect in Chengdu is greater than in Wuhan. WY in the suburbs of Wuhan is severely impacted by urban expansion, while WP in the suburbs of Chengdu is as well. HQ in Chengdu's city center suffers the largest negative impact. The study also reveals a spatial spillover effect of urban expansion, with extensive negative externalities on all WESs in the city centers of both cities and positive externalities on WY and WP in the southwestern suburbs of Chengdu. Based on these results, we suggest that megacities in developing countries should focus on protecting HQ in the city center and limiting cross-regional edge-based expansion in suburbs. Attention should be paid to the water-ecological protection of the suburb rivers. City managers should consider ecological zoning geared toward the conservation of WESs to address the adverse impacts of expansion. [ABSTRACT FROM AUTHOR]