How green can it be? A methodology for calculating green roof retrofit potential in Valencia

Cities are accountable for more than 70% of global CO2 emissions and consume around 65% of the world's energy. In the pathway towards urban decarbonisation, nature-based solutions rise as a promising opportunity. They improve a city's resilience, stabilise temperatures and capture CO2, both mitigating climate change effects and adapting to them. This paper presents a novel methodology to assess the potential effects of green roof retrofit in urban areas, selecting suitable buildings for greening and estimating their decarbonising capacity. The proposed method combines the use of Geographic Information Systems (GIS) and artificial vision algorithms to select the roofs. Once selected, direct carbon sequestration and energetic savings are estimated based on empirical results. This methodology is successfully applied to the L'Illa Perduda neighbourhood of Valencia (Spain) as a case study. The GIS analysis shows that about 50% of the roofs' surface could be greened, directly absorbing around 350 tCO 2 yr −1 and reducing the energetic emissions of the neighbourhood in about 100 tCO 2 yr −1 by improving the insulating envelope of the buildings. The artificial vision computation selected 38% of the surface of the neighbourhood residential buildings. • Novel method to assess the decarbonisation potential of urban green roof installation. • The methodology combines GIS and artificial vision to select suitable roofs. • The potential area to be greened and the energy savings are estimated. • The direct and indirect atmospheric carbon reduction by green roofs is estimated. • Half of the studied rooftops in one of Valencia's neighbourhoods could be greened.