Clever and cool Generating design guidelines for climate-responsive urban green infrastructure Wiebke Klemm Clever and cool Generating design guidelines for climate responsive urban green infrastructure Wiebke Klemm Thesis committee Promotor Prof. Dr A. van den Brink Professor of Landscape Architecture Wageningen University & Research Co-promotors Dr S. Lenzholzer Associate professor, Landscape Architecture Group Wageningen University & Research Dr L.W.A. van Hove Assistant professor, Meteorology and Air Quality Group | Water Systems and Global Change Group Wageningen University & Research Other members Prof. Dr E. Turnhout, Wageningen University & Research Dr G.J. Hordijk, Delft University of Technology Prof. Dr M. Prominski, Leibniz University Hannover, Germany Prof. Dr P.J.V. van Wesemael, Eindhoven University of Technology This research was conducted under the auspices of the Graduate School for Socio-Economic and Natural Sciences of the Environment (SENSE). Clever and cool Generating design guidelines for climate responsive urban green infrastructure Wiebke Klemm Thesis submitted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus, Prof. Dr A.P.J. Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Monday 19 November 2018 at 1:30 p.m. in the Aula. Wiebke Klemm Clever and cool Generating design guidelines for climate-responsive urban green infrastructure, 292 pages. PhD thesis, Wageningen University, Wageningen, the Netherlands (2018) With references, with summaries in English, Dutch, German ISBN 978-94-6343-305-1 DOI https://doi.org/10.18174/453958 Voor Michiel, Lieke & Renske Propositions 1. Climate-responsive urban green infrastructure must not be ubiquitous, but clever. (this thesis) 2. Knowledge on subjective thermal perception is essential for climate-responsive urban design. (this thesis) 3. A pragmatic worldview in scientific research is key for creating real life solutions. 4. Short-term thinking contradicts an ‘urban living lab’ way of working. 5. Guiding principles are good, background knowledge is better. 6. Not explicitly taking into account climate change adaptation in the new Dutch Environment and Planning Act (Omgevingswet) is not only a missed opportunity but also an ethical misjudgement. 7. Empathic abilities are critical for successful collaboration. Propositions belonging to the thesis, entitled Clever and cool – Generating design guidelines for climate-responsive urban green infrastructure Wiebke Klemm Wageningen, 19th november 2018 Table of contents 1 Introduction 9 1.1 Motivation 11 1.2 Global warming and urban heat stress 13 1.3 Landscape architecture and climate-responsive design 14 1.4 Urban green infrastructure 16 1.5 Urban green infrastructure impacts on urban microclimate and human thermal comfort 18 1.6 Need for useful design guidelines 24 1.7 Knowledge gap and research questions 28 1.8 Research design 30 1.9 Structure of the thesis 38 2 Psychological and physical impact of urban green spaces on outdoor thermal comfort during summertime in the Netherlands 41 2.1 Introduction 44 2.2 Methods and materials 47 2.3 Results and discussion 55 2.4 Conclusion 61 3 Towards guidelines for designing parks of the future 65 3.1 Introduction 68 3.2 Methods and materials 70 3.3 Results and discussion 77 3.4 Conclusions: design guidelines for future parks 88 4 Street greenery and its physical and psychological impact on thermal comfort 91 4.1 Introduction 94 4.2 Methods 96 4.3 Results and discussion 105 4.4 Conclusions 114 5 Qualitative methods to explore thermal perception in outdoor urban spaces 117 5.1 Introduction: concepts and methods in outdoor thermal perception research 120 5.2 Method and results: Literature review on methods to study spatial aspects of thermal perception 125 5.3 Discussion and conclusions: which method when? 144 6 Development of green infrastructure design guidelines for urban climate adaptation 151 6.1 Introduction 154 6.2 Study design 156 6.3 Methods 161 6.4 Results 163 6.5 Discussion and conclusion 173 7 Discussion and conclusions 177 7.1 Introduction 179 7.2 Answering the research questions 181 7.3 Discussion 196 7.4 Methodological reflections 208 7.5 Future research 210 7.6 Relevance for society and professional practice 212 Appendices 217 References 239 Summary 255 Samenvatting 263 Zusammenfassung 273 Acknowledgements 283 About the author 287 1 Introduction 1.1 Motivation 1 In 2010, I presented a design proposal for a climate-responsive neighbourhood at a symposium for environmental professionals. The design proposal was the result of the study ‘Climate change adaptation in the city’ that I had worked on with colleagues from the landscape and urban design office, Bosch Slabbers, in commission of the (former) Dutch Ministry of Housing, Spatial Planning and the Environment. The project’s aim was to showcase integrating climate change adaptation in landscape architectural design as a response to the challenges of global warming and urbanization in the Netherlands. At the time, climate change adaptation was a rather new topic in the Netherlands, both for policy makers and for landscape architects, and other urban planning and design professionals. It was difficult to find appropriate knowledge on or guidance for designing outdoor spaces that contributed to urban climate adaptation. Little was known, especially about heat-related climate-responsive urban design which means shaping outdoor spaces that are thermally comfortable and facilitate usage and activity all year around (Brown, 2010). Such thermally comfortable spaces address the adverse effects of global warming and urban heat stress, and take advantage of the positive microclimate effects, namely longer warm periods which make outdoor activities attractive. Climate-responsive design in terms of water storage, for example, was less critical as Dutch planners and designers have a long- standing tradition in designing with water (e.g., Teeuw et al., 2005, Pötz et al., 2010, Van de Ven, 2009). Designing thermally comfortable outdoor spaces, in contrast, was new in the Dutch context. We collected available information on climate-responsive urban design mainly from Germany, where urban design has been related to urban climate issues for a longer period (Ministry of Transport and Infrastructure Baden-Wuerttemberg, 2008). The general positive effects of green became clear from our literature research. Urban vegetation, in particular tree canopies, provides shade and moderates solar heat gain through evapotranspiration. We then studied green design interventions, such as the decrease of hard, and the increase of preferably green, permeable surfaces (e.g., the increase of lawns and trees in outdoor spaces), and applied them in design proposals. One of them was the design proposal for a climate-responsive neighbourhood in Transvaal, The Hague, which I presented at the symposium. 11 At the end of the presentation, a policymaker asked: “This is a nice neighbourhood design. How much cooling will this design proposal provide after implementation?”. With mostly general, qualitative information at hand, answering this question was not easy. Studies on the quantitative impacts of urban green on urban climate conditions were deficient, so providing the requested knowledge was impossible. However what followed was a lively discussion between attending policymakers, researchers, and urban designers on the essence of heat- related climate-responsive urban design, and in particular, the role of urban green spaces and elements. This discussion opened my eyes. I became interested in the actual cooling impact of urban green spaces and elements, and how this type of quantitative knowledge could help urban designers to shape thermally comfortable urban spaces. Eventually, to contribute to creating useful knowledge and advancing urban climate adaptation, I decided to exchange my work place at the design office for the position of a PhD researcher at Wageningen University within the Climate-Proof Cities project cluster of the Dutch ‘Knowledge for Climate’ programme. Since the start of my PhD research, public and political awareness of urban heat and its negative impacts on health and well-being has significantly raised. This is partly due to more frequent heat waves in the Netherlands in the last couple of years (e.g., Boezeman and Kooij, 2015). The awareness of urban heat stress increased interest in adapting urban areas to changing thermal conditions. At all policy levels (e.g., European Environment Agency, 2015, City of Amsterdam, 2015, European Environment Agency, 2010), more and more attention has been given to the need to develop climate-responsive urban areas by means of urban greening. What is still lacking is specialised knowledge on heat-related climate-responsive design of urban green elements and spaces: What is the actual cooling effect of urban parks or street trees? And, how should landscape architects and urban designers shape vegetation structures in urban parks, streets or residential gardens to be thermally comfortable, not only on hot summer days, but also all year round to enable outdoor activity? Currently it seems that the general belief of ‘green is good’ appears to be sufficient to inform design. The adage seems to be: ‘the greener, the better urban spaces are adapted to urban heat issues’. Ubiquitous urban green solutions are presented as a panacea for all urban climate issues. However, it is obvious