To green or not to green! That is the question. Does green infrastructure provide significant thermo-regulation in a maritime temperate climate?

Abstract

Presenting author 1,2 Joint first authors AbstractThe ecosystem service delivery of urban green infrastructure (UGI) is now manifest. Types and level of service provision, however, can alter radically, based on factors such as location, species choice, planting design and vegetation management. The value of vegetation to provide a cooling service is generally understood in hot climates, but the merit in temperate climates remains ambiguous. Indeed, policy makers within cooler countries (e.g. UK) remain to be convinced that expenditure on UGI is justified, at least from the point of view of city cooling alone. Occasional warm days do occur of course, and climate change models predict that heat wave events will become more frequent within the UK, including those that pose a risk to human health. To help UK policy makers make better-informed decisions around UGI, a number of our research programmes have targeted the role vegetation plays in regulating temperature, but specifically within the context of a maritime-temperate climate Two examples of green interventions are discussed here. The first documents the role of green façades to cool a wall system and the second illustrates the cooling influence conferred by roadside trees. Both experiments used a replicated sampling approach to ensure statistical robustness, and hence convince policy makers that data is representative of UK scenarios and results are reproducible. In the first experiment, 10 separate wall sections are used to investigate the cooling influence of two different plant genotypes (Prunus and Phaseolus) on both exterior and interior wall spaces. In the second study, road surface temperatures are documented with respect to both built and green infrastructure, i.e. we compare the influence of buildings and street trees on the surface temperatures across a road profile Again replicate data are used to provide a generic summer temperature profile for the city of Sheffield, rather than just specific locations at one point in time. Results show that green facades can reduce exterior and interior (cavity) wall air temperature by 3 o C and 5 o C respectively. Likewise, large street trees have a mean cooling influence of 4.5 o C on road surfaces near their base compared to comparable sections adjacent to buildings. To maximise cooling, the data suggests that trees need to be provided on both sides of a roadway, i.e. a single tree did not manage to cool the pavement at the opposite side of the road. The implications of the results for temperate climates are discussed.