Abating heat waves in a coastal Mediterranean city: What can cool roofs and vegetation contribute?

The frequency and intensity of heat waves (HW) in cities are on the rise due to climate change as well as urban fabric materials and anthropogenic activities that affect heat accumulation. The efficacy of HW mitigation strategies depends on a city's specific and unique morphology, land use, building materials, climate and geography. In this study, we show the effectiveness of cool roofs and vegetation in reducing temperature in the Metropolitan Area of Barcelona (AMB). We use the Weather and Research Forecasting (WRF) model with the urban scheme BEP+BEM, including11 urban classes to simulate a HW that occurred in August 2015. We find that cool roofs reduce temperature best during the day (0.67 °C average and 2.22 °C maximum reductions), while additional green areas moderate temperatures to a lesser degree but also more evenly during the day and at night (average reductions of 0.15 °C and 0.17 °C, respectively). However, when irrigation is increased, the temperature reduction during the day is intensified due to the cooling effect of more evapotranspiration. The thermal regulation of combining the two strategies is the most evenly distributed over the AMB and has the highest impact, with an average and maximum reduction of 1.26 °C and 4.73 °C at 13:00UTC.