Seite - 38 - in Biodiversity and Health in the Face of Climate Change

38 The trend towards an increasing frequency and severity of heat-related events is significant not only due to impacts on human health, but also due to the implications for energy demand for space cooling as people start to autonomously adapt. Even in relatively cool Manchester, modelling studies suggest that the summer UHI increases air conditioning loads by ~7–8% (Skelhorn et  al. 2017). The UHI effect is then an additional factor to consider  on top of the estimated mean of 13 cooling degree days per year (days where the mean temperature exceeds 22  °C) under the high emissions scenario central estimate for the 2050s (Cavan 2010). More chiller energy is likely to be required to maintain comfortable temperatures, particularly for people who have higher sensitivities to ill-effects, e.g. due to age or pre-existing health conditions (Lindley et  al. 2011). It is also highly likely that autonomous adaptation will lead to increases in air conditioning, but only for those who can afford it. One of the drivers of increasing UHI is urban densification and associated losses of green cover. For example, green cover around Manchester’s urban weather sta- tion has reduced by ~11% (2000–2009). Impacts are corroborated by modelling, showing that replacing all vegetation with asphalt would lead to air temperature increases of up to 3.2  °C in parts of the city (Skelhorn et  al. 2014). Presence and abundance of biomass are two of the biodiversity metrics that are positively con- nected with moderation of extreme events and local climate/air quality regulation  (Fig. 2.4) along with taxonomic diversity, species composition, func- tional diversity and functional identity. In addition to green space losses a range of other ecosystem and biodiversity met- rics are influential in affecting spatial and temporal patterns in the urban micro- climate, such as species type and functional traits. There is also the issue of green space degradation and/or modification due to urban factors, including through impacts on biodiversity. Urban ecosystems have distinct abiotic characteristics: higher temperatures, modified/drier soils, higher surface sealing, higher light levels due to artificial lighting and more fragmentation (Schwarz et  al. 2017). Urban eco- systems also differ in their composition, functional traits and structures as a result of abiotic factors and management practices (Ziter 2016; Schwarz et  al. 2017). The effect can be to modify regulating functions, sometimes reversing beneficial func- tions for health and well-being. For example, inappropriate management of a large, 30-year-old green roof in Manchester was found to increase both air and surface temperatures. Peak air temperatures above a damaged green roof exceeded those above an adjacent bare roof during some of the hottest periods of an experimental study (Speak et  al. 2013a, b). In the damaged roof case, impacts were exacerbated by the removal of vegetation (largely grasses) during an extended drought period. Natural re-colonization to a ‘meadow’ form took two growing seasons during which time temperature regulating functions continued to be compromised, as well as the other functions that the green roof had been providing, including air pollution removal and regulation of water runoff and water quality (Speak et  al. 2012, 2013a, b, 2014). Clearly, for green spaces to be able to retain their beneficial functions, it will be necessary to adapt associated management practices and consider what sorts of met- rics are used to assess change. Fortunately, in terms of temperature, a relatively S. J. Lindley et al.