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• A multi-objective optimization and analysis framework for HGGI is proposed. • A trade-off between costs and systematic resilience for HGGI design is developed. • The HGGI layouts with different degree of decentralization is compared. • Importance of spatial allocation for HGGI is highlighted in different urban areas. The trade-offs for alternative grey-green infrastructure (HGGI) solutions between life cycle cost (LCC) and systematic resilience may impose many limitations in planning and implementation of urban stormwater strategies in high-dense urban catchment. This study presents a generic approach in the context of a multi-objective optimization, with the aim to (1) optimize and design HGGI under various uncertainties, and conflicting objectives (e.g., LCC, technological and operational resilience); and (2) determine the trade-offs between the multi-objectives and degrees of system decentralization in areas with various development intensities. Taking two areas in Guangzhou, China, as case studies, this study shows that decentralized HGGI exhibits economic advantages. However, to maintain a high systematic resilience in high-density catchments, it is often necessary to rely on solutions with high degree of centralization, which may incur higher cost. HGGI is found to perform better in terms of technological resilience under extreme storms, than operational resilience to the uncertainty associated with structure performance. In addition, porous pavement is found to exhibit high potential for wider application compared to bioretention cells as green infrastructure in HGGI. The framework developed in this study could support decision-making for stormwater management via enhancing both hydraulic reliability and hydrologic resilience. [Display omitted] [ABSTRACT FROM AUTHOR]

Rapid urbanization and global climate change are increasing the vulnerability of cities to urban flooding, thereby posing significant challenges to the design and implementation of urban drainage systems (UDS). Traditional centralized UDS have been found ineffective in mitigating the uncertainty of future flood risks. Consequently, the need to explore resilient alternatives, such as decentralized UDS, has gained importance. Of particular interest is the coupled approach of grey infrastructure (GREI) and low-impact development (LID), which merges the drainage capabilities of GREI with the versatility and sustainability of distributed green infrastructure. However, there are limited studies assessing the environmental and economic impacts of both centralized and decentralized LID-GREI UDS using integrated Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods. This study, using Zhujiang New Town, Guangzhou, China, as a case study, found that decentralized UDS outperformed centralized UDS from both environmental and economic perspectives, mainly due to smaller pipeline scale and lower maintenance frequency. Furthermore, though the LID-GREI UDS showcased more substantial environmental impacts and higher economic costs compared to GREI UDS, the hydrological benefits obtained from LID operation can counteract part of these environmental impacts. In a unique perspective, this study considers the payback periods for centralized and decentralized LID-GREI UDS, estimating them to be 70 and 55 years respectively, when taking economic implications and hydrologic benefits into an overall consideration. Overall, the findings underscore that the LID-GREI UDS, particularly the decentralized LID-GREI, presents a more sustainable and cost-effective strategy for mitigating pluvial flooding compared to GREI UDS. This study provides comprehensive insights into effective and cost-efficient strategies for alleviating urban flooding vulnerabilities through UDS design and implementation. • Lifecycle scrutiny conducted on centralized and decentralized UDS. • Investigation covers environmental, economic impacts, and hydrological merits. • Decentralized UDS shows reduced environmental and economic burdens. • Centralized, decentralized LID-GREI's payback spans 70 and 55 years, respectively. • LID-GREI UDS surpasses GREI UDS in sustainability and cost-effectiveness. [ABSTRACT FROM AUTHOR]

Concentrations and compositions of PAHs and oxygenated PAHs (OPAHs) in four size ranges of ambient particles (< 1.1, 1.1–3.3, 3.3–9.0 and > 9.0 μm) collected in Xi'an and Guangzhou, two megacities of China, during the winter and summer of 2013 were measured and compared with those in 2003. The TSP-equivalent concentrations of Σ14PAHs in Xi'an and Guangzhou are 57 ± 20 and 18 ± 23 ng m − 3 in winter, 5–10 times higher than those in summer. PAHs in both cities are dominated by 5- and 6-ring congeners in summer. In contrast, they are dominated by 4- and 5-ring congeners in winter, probably due to enhanced gas-to-particle phase partitioning of the semi-volatile PAHs. TSP-equivalent Σ7OPAHs during winter are 54 ± 15 and 23 ± 32 ng m − 3 in Xi'an and Guangzhou and dominated by 5-ring OPAHs. Size distribution results showed that the fine modes (< 3.3 μm) of PAHs and OPAHs in both cities are dominated by 4- and 5-ring congeners in winter and 5- and 6-ring congeners in summer. Relative abundances of 3-ring PAHs and OPAHs increased along with an increase in particle sizes, accounting for from about 1% of the total PAHs or OPAHs in the smallest particles (< 1.1 μm) to > 90% of the total in the largest particles (> 9.0 μm). The toxicity of PAH assessment indicated that atmospheric particles in Xi'an and Guangzhou during winter are much more toxic than those during summer and fine particles are more toxic than coarse particles. Compared to those in 2003, fine particulate PAHs and OPAHs in both cities during winter decreased by 50–90%, most likely due to the replacement of coal by natural gas in the country. [ABSTRACT FROM AUTHOR]

• Supply-demand assessment and proximity matrix analysis are integrated for SCC. • 62.5% of the townships in Guangzhou's central districts show a relatively imbalanced "supply-demand". • Exposure and vulnerability are considered to assess the demand for SCC facilities. • Planning reference networks are established based on complex network relationships. Sponge City Construction (SCC) has been extensively explored for controlling frequent urban waterlogging and non-point source pollution. Assessing the "supply" and "demand" of SCC as a city-wide approach may aid in appropriate areal coverage to achieve optimal performance on flood control based on local priorities and sustainable urban development plans. However, to date, very few studies have examined the potential spatial mismatches in the "supply" and "demand" of SCC. This study presented the development of a framework to explore the supply–demand relationship based on a spatial multi-criteria evaluation of the existing SCC facilities, risk exposure, and socio-economic vulnerability. The feasibility and application of such a framework were successfully demonstrated in a field application in Guangzhou, China. The results indicated that most of the high-density areas in the city centres of Guangzhou were exposed to high risk with strong SCC demands. Furthermore, Liwan and Yuexiu districts exhibited SCC supply deficits, while SCC supply surpluses were observed in other central districts in Guangzhou. The findings of this study provided insight into the development of a generalised and replicable method that could be used to achieve a balance between the "supply" and "demand" of SCC for more participatory, strategic and multifunctional planning of SCC in various urban contexts. [ABSTRACT FROM AUTHOR]