The potential of tree planting to climate-proof high density residential areas in Manchester, UK

Tree cover differs widely between different urban morphology types, being particularly low in high density residential areas. However, even within these areas there is great deal of variability. This matters because trees provide environmental benefits such as cooling, which is likely to become more important with predicted climate change. This study investigated how differences between types of high density terraced, semi-detached and courtsquare housing affects the surface cover and land use within Greater Manchester, UK. We also investigated the extent to which tree cover could be increased in each housing type. The maximum surface temperature of housing types with current and potential tree cover was modelled with the Tso model to see whether tree planting could keep them at current levels. Tree cover ranged from 1.6% to 14.8% across the 11 high density housing types in this study, being highest in larger houses with large gardens or more modern houses with more open space. Planting could potentially increase tree cover only by between 2.8% and 5.3%, with the greatest increase found in 1960s driveway housing. Potential tree cover was less variable because most new trees would be planted into pavement, which was equally common in all housing types. Computer modelling showed tree planting could reduce maximum surface temperature by between 0.5 °C and 2.3 °C. The highest reductions occurred in housing types with the lowest tree cover, but in no housing type could new tree planting keep temperatures to current levels even to the 2020s.

► Tree cover is low in density residential areas of Manchester, UK, only 6.6%. ► Tree cover differed widely between housing types, being greater in semi-detached housing than terraces and greater in newer housing than old. ► The potential to increase tree cover by planting was low: only 3.7% on average, because of the limited planting area and need for wide spacing of street trees. ► Modelling showed that tree planting could reduce surface temperatures by up to 2.3 °C, but not by enough to climate proof high density housing.