Sustainable urban stormwater management for climate-resilient communities

Abstract

Climate change and the intensification of human activities have brought enormous challenges to the urban water environment. Urban waterlogging, induced by the excessive accumulation of stormwater runoff, can adversely affect the functionality of urban infrastructure and the daily activities of residents. Nitrogen in runoff is particularly problematic, potentially leading to eutrophication of freshwaters and with implications for environmental and human health where it occurs in excess. Nature-based Solutions (NbS) in urban communities are an important contributor to addressing these challenges. For example, bioswales, rain gardens and permeable pavement can remove nitrogen from runoff and reduce the volume of urban runoff reaching rivers. Although NbS can effectively mitigate the urban runoff challenges intensified by climate change, there is still a notable research gap concerning the strategic mechanisms for altering the configuration of NbS and integrating stormwater management practices to enhance climate change adaptation at specific locations. The key findings in this study are shown as follows:

1. To investigate local strategies for climate change adaptation, the Cicheng New Town in Ningbo, China, was selected as a case study area. Performance differentials of urban runoff treatment by NbS under climate change scenarios (i.e., SSP2-4.5, SSP3-7.0, and SSP5-8.5) were measured using Storm Water Management Model (SWMM) simulation. According to the modelling results, there was a 6% decline in NbS performance across all climate scenarios. Bioswales are simple structures with a small footprint and easy maintenance and are a critical component of ecological habitats for addressing urban runoff issues. To explore the addition of a particular infrastructure to adapt to the impacts of climate change, the minimum required bioswale coverage for new development was established in this study to be 4% of the community area to offset these impacts.

2. Rain gardens and permeable pavements are less expensive per unit area than bioswales in Chinese communities. Therefore, combining these three types of facilities could counteract the impact of climate change in a more economically viable manner. To identify suitable, cost-effective solutions that satisfy the demands of offsetting the effects of climate change, as well as other decision-maker preferences (i.e., maximum runoff volume reduction or total nitrogen reduction), the best spatial configuration for increasing these three types of facilities was optimised by combining the non-dominated Sorting Genetic Algorithm (NSGA-II) and SWMM. Using multi-objective optimisation, eight highly cost-effective strategies were identified across four preference scenarios targeting runoff and nitrogen control in both high- and low-income communities. Compared to similarly priced alternatives, runoff-focused strategies achieved 0.86% to 13.9% greater reduction in runoff, while nitrogen-focused strategies improved total nitrogen removal by 0.08% to 8.45%. A 15-year cost-benefit assessment revealed that low-cost options yielded higher benefit-cost ratios than high-investment ones. The proposed framework offers a reliable approach for optimising NbS to support climate adaptation in diverse urban communities.

3. Structural measures often require the assistance of other non-structural measures to be effective, such as source control and pollution prevention, public education and regulatory controls. The issues that sponge cities face are mostly related to flooding, with little attention paid to urban environmental degradation. Self-Purifying City was proposed as a possible way to improve the urban environment by using natural processes based on low-cost, low-carbon, artificially enhanced technologies and management. This study systematically reviewed 693 academic publications from the Web of Science and 1539 legal documents from the Ecolex environmental law database, identifying 36 stormwater purification strategies and 141 relevant environmental laws. Through comprehensive multi-dimensional analysis and synthesis of evidence, it examined the characteristics and interlinkages of these strategies and legal instruments, leading to the development of a transformative framework for stormwater management. The proposed framework advocates context-sensitive, community-driven, and strategically aligned interventions across commercial operations, financial instruments, individual behaviour, and institutional regulation. It puts forward five key measures: integrating NbS into mainstream planning, instituting mandatory long-term monitoring, establishing dedicated financial mechanisms with incentive and penalty structures, enhancing stakeholder coordination through legal provisions, and applying data-informed approaches to manage high-risk areas. To illustrate its practical utility, the framework is applied to nitrogen pollution control, thereby contributing to environmental protection and supporting the transition towards Self-Purifying Cities.

The combined findings of this study provide methods for spatial optimization of NbS for urban designers and support municipal officials in making decisions about urban stormwater management. Due to the modest scale of the current study which focuses on urban communities, larger-scale studies will be conducted in the future, such as exploring the spatial patterns and driving mechanisms of NbS at the global city scale. Whilst this study shows that bioswales and other NbS are likely to be important in reducing nitrogen pollution in the future, future work could usefully explore impacts on other pollutants, such as trace metals, microplastics, pesticides, and persistent organic pollutants. The evidence synthesis employed in this study for compiling non-structural measures was based on manual extraction and analysis of pertinent text. In future studies, machine learning could be applied to extract relevant data from published literature or databases and actively predict robust scientific claims, thereby facilitating urban stormwater management. From an ecological perspective, the main findings of NbS as proposed in this study supports the enhancement of urban biodiversity, the rehabilitation of degraded aquatic ecosystems, and the strengthening of key ecosystem services, each of which is critical to fostering resilient and sustainable urban environments.

Date of Award	15 Jul 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Faith Chan (Supervisor), Fangfang Zhu (Supervisor), Matthew F. Johnson (Supervisor) & Yaoyang Xu (Supervisor)