Remote Sensing and GIS for Modelling Green Roofs Potential at Different Urban Scales

Introduction

The United Nations’ 2030 Agenda for Sustainable Development (SD) defined 17 SD goals for the next fifteen years. The aim is to achieve a better and more sustainable future, by addressing global challenges like poverty, inequality, climate, environmental degradation, prosperity, peace, and justice (United Nations, 2016). Among these goals, Goal 11 is dedicated to Sustainable Cities and Communities, and its targets include, among others, increasing the number of cities and human settlements that adopt and implement integrated policies and plans for mitigation and adaptation to climate change.

Green infrastructures such as trees, plants, or forests are vital assets that through spatial planning can help cities adapt to climate change (Demuzere et al., 2014; Zölch et al., 2016). They provide services like managing high temperatures and flooding or reducing greenhouse gas emissions through direct carbon sequestration (Chen, 2015; Jayasooriya & Ng, 2014; Klemm, Heusinkveld, Lenzholzer, & van Hove, 2015; Muñoz-Vallés et al., 2013; Norton et al., 2015; Yang & Wang, 2017). Green infrastructures also have other social, economic and environmental benefits like improving health and well-being by filtering air pollutants and increase recreational opportunities, reducing buildings energy usage and heating and cooling costs by providing shading and wind-blocking, or fostering biodiversity through habitats provision (Camps-Calvet et al., 2016; Connop et al., 2016; Elmqvist et al., 2015; EPA - United States Environmental Protection Agency, 2014; Tzoulas et al., 2007).

Sustainable development requires green spaces but, in densely built city centers, unoccupied land is rarely available, and green spaces are few and far between (Haaland & van den Bosch, 2015; Jim, 2004). The loss of green urban areas during the last decades and the consequent soil sealing opened the way to novel mitigation strategies for restoring the environment and protect human health. Typically, open green spaces are the most desired interventions; nevertheless, available space is generally sparse for this purpose. However, roofs are valuable empty grey spaces that can be used to compensate for the lack of permeable land and help cities adapt to climate change (Bates et al., 2013; Francis & Lorimer, 2011; Haaland & van den Bosch, 2015; Santos et al., 2016). Green Roofs (GR) are strategies to promote urban greenspace, and that can be explored in a sustainable development context. GR constitute a solution to restore the environmental quality in densified neighborhoods, providing benefits for the buildings, and for the community as well (Getter & Rowe, 2006; Jim, 2013), in the context of energy transition in the built environment.

For property owners, the installation of a GR reduces the amount of energy needed to maintain the indoor temperature. In fact, GR improve the thermal performance of buildings by reducing the thermal load in the summer and promoting insulation in the winter (Saadatian et al., 2013). Lowering the buildings’ heating and cooling cost with air-conditioning improves energy efficiency. This reduced energy consumption also lowers the building carbon footprint, thus helping to promote low-carbon communities (Ascione et al., 2013; Lehmann, 2014). Furthermore, the presence of a green cover increases the longevity of the waterproof membrane, decreasing the exposure to large temperature fluctuations and ultraviolet radiation (Bianchini & Hewage, 2012). Increasing membrane durability also reduces material waste. Another benefit is the improved acoustical insulation characteristics of the roof. The green coverage attenuates the noise inside the building by mitigating the sound waves over the roof (Saadatian et al., 2013).

Public benefits include Urban Heat Island (UHI) mitigation through shadowing and evapotranspiration. GR provides several ecosystem services: biodiversity and habitat, pollution control, improved air quality and carbon storage. Furthermore, they act as an effective stormwater retention management tool by reducing the amount of rainwater discharged into the sewers (Brandão et al., 2017); also, in peak flows the tempering effect allows designing drainage systems with reduced diameters. Other benefits include sound absorption leading to reducing noise exposure levels, aesthetical benefits and new green jobs in the local economy. Furthermore, GR can offer a novel space for leisure activities and can be used as educational laboratories or even can serve other functions like local food production.