Nature-based solutions for urban heat islands in megacities: a case study in Shenzhen, China

Abstract

The phenomenon of rapid urbanisation has fundamentally transformed the spatial configuration of cities worldwide, engendering a plethora of complex urban development challenges. Among these challenges, the most pronounced and intractable issues are found within high-density urban agglomerations, where social and environmental problems converge. This is particularly in the context of China's ongoing urbanisation process, where the proliferation of urban villages (Chengzhongcun in Chinese) and their attendant effects on the ecological environment are manifested through the observable degradation of the urban thermal environment. The urban heat island effect, considered one of the most prominent consequences of urbanisation, has been observed to intensify significantly in densely populated urban areas. This exacerbates various challenges associated with air quality, energy consumption, and human health.

The emergence and expansion of urban villages in China are often considered a byproduct of rapid urbanisation, resulting in a range of problems, including overcrowding, poor sanitation, and inadequate infrastructure, which pose significant challenges to urban sustainability and liability. As a response to the aforementioned challenges, policymakers and urban planners in China have adopted to systematically demolish and redevelop high-rise luxury. However, this mode of urban regeneration has had the unintended consequence of creating a city fabric that is becoming increasingly homogeneous, while also reducing the diversity, sustainability, and adaptability of the urban area.

Within the context, this study has developed a set of strategies aimed at mitigating the detrimental effects of the urban heat island phenomenon in megacities. Specifically, the strategies revolve around the adoption of nature-based solutions, which entail the utilisation of natural systems and processes to tackle environmental problems and enhance the quality of life. The study places a particular emphasis on multiple methods to implementation of nature-based solutions at various scales in high-density urban areas, thereby providing a comprehensive framework for addressing the issue.

This study is centred on three core research problems: (1) the scale of megacities has become a problem (environmental issues in megacities and the social problems of population and housing density in urban area); (2) an underestimation of the phenomenon of urban villages in China; (3) potential problems associated with the wholesale demolition measure in urban village redevelopments.
Based on these conditions, the study is guided by the following three research questions:
(1) “Why consider the proposed “Nature-based solutions” against “Demolition & Reconstruction” of urban villages in Chinese megacities? How can nature-based solutions provide sustainable alternatives to traditional infrastructure-based approaches for mitigating the environmental and social impacts of megacities?”
(2) “Are urban villages, a spatial phenomenon of the 21st century urbanisation in China, causing urban heat island effect?”
(3) “How to design nature-based solutions to mitigate urban heat island effect and improve thermal comfort in the megacities?”

A three-phase research methodology is proposed to address the three research questions. This methodology includes a transdisciplinary literature review, a hybrid simulation approach, and a research-by-design methodology, each designed to address a specific research question. The first phase involves conducting a comprehensive literature review across multiple disciplines. The second phase utilises a hybrid simulation approach that combines various modelling and simulation techniques. The final phase employs a research-by-design methodology tailored to the third research question. By applying this three-phase research methodology, this PhD thesis aims to provide a comprehensive understanding of the research questions and contribute valuable insights to the field of landscape architecture, with Baishizhou serving as a representative case study site.

The most important and crucial findings from this thesis are as follows:
1. This PhD thesis affirms the potential efficacy of nature-based solutions in ameliorating the urban heat island effect within the context of Shenzhen, China. It underscores the prioritisation of NBS over the conventional practices of urban demolition and reconstruction.
2. The research methodology employed in this study encompasses a multidisciplinary approach, encompassing an extensive literature review, environmental simulation, and research through design. Notably, this thesis introduces an innovative environmental simulation methodology facilitated through the Grasshopper platform, allowing for the integration of multiple software
tools to simulate environmental characteristics across various scales. This innovative research approach optimises the landscape architecture and urban planning design processes, thereby enhancing overall design efficiency.
3. During the design phase, this thesis introduces the conceptualisation of an urban forest framework aimed at mitigating the urban heat island effect and enhancing thermal comfort within the urban environment. This urban forest concept, as a manifestation of nature-based solutions, encompasses three spatial scales: the micro-scale encompassing the vertical forest concept, the meso-scale encapsulating the neighbourhood forest concept, and the macro-scale representing the urban forest concept at the district level.

In addition to proposing a novel approach to urban regeneration, this thesis offers a comprehensive analysis of the multiple scales at which nature-based solutions can effectively mitigate urban heat island effect in Shenzhen. By focusing on Baishizhou, an urban village in Shenzhen, the study underscores the critical role of nature-based solutions in addressing the challenges of climate change, environmental pollution, and heatwaves faced by megacities such as Shenzhen. Through a collective methodology that synthesises and integrates insights from multiple disciplines, the thesis provides robust evidence of the potential benefits of nature-based solutions in urban heat islands mitigation in the case study.

Overall, this study highlights the importance of prioritising nature-based solutions in urban planning and development strategies, as a means of promoting more sustainable and resilient cities in the face of global climate change. The findings of this study underscore the urgency of adopting innovative approaches to urban regeneration that leverage nature-based solutions to enhance the connection between nature, humans, and cities, thereby fostering greater urban sustainability and resilience.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Greg Keeffe (Supervisor), Jasna Mariotti (Supervisor) & Neil Galway (Supervisor)