Cool roofs could be most effective at reducing outdoor urban temperatures in London (United Kingdom) compared with other roof top and vegetation interventions: a mesoscale urban climate modeling study

Comprehensive studies comparing impacts of building and street levels interventions on air temperature at metropolitan scales are still lacking despite increased urban heat-related mortality and morbidity. We therefore model the impact of 9 interventions on air temperatures at 2 m during 2 hot days from the summer 2018 in the Greater London Authority area using the WRF BEP-BEM climate model. We find that on average cool roofs most effectively reduce temperatures ($\sim$~-1.2~$^\circ$C), outperforming green roofs ($\sim$~0~$^\circ$C), solar panels ($\sim$~-0.5~$^\circ$C) and street level vegetation ($\sim$~-0.3~$^\circ$C). Application of air conditioning across London (United Kingdom) increases air temperatures by $\sim$~+0.15~$^\circ$C. A practicable deployment of solar panels could cover its related energetic consumption. Current practicable deployments of green roofs and solar panels are ineffective at large scale reduction of temperatures. We provide a detailed decomposition of the surface energy balance to explain changes in air temperature and guide future decision-making.