Modelling the optimal green roof type for carbon capture in an urbanised university campus

Abstract

Carbon capture has been brought to the forefront of research in an effort to battle the climate crisis, but the physical space needed to implement necessary green infrastructure is sparse and only diminishing. Therefore, efforts to adapt and repurpose current infrastructure to house essential green space must be made. Green roofs offer a sustainable, nondestructive solution that can help to address climate-related issues in urbanised areas, such as poor air quality, lack of green space, and the urban heat island effect. Previous studies have highlighted the potential of green roofs in an urbanised environment with regard to these benefits, however, further scope remains to identify the combination of vegetation that present optimal efficiency for carbon sequestration in a temperate climate. This study focuses on improving the University of Bristol’s initial attempt of green roof implementation and provides a guideline for further expansion with emphasis on maximising carbon capture. Initially, a diverse range of plant samples were considered. Then, the appropriate plant species were analysed comparatively in laboratory testing to differentiate their rates of photosynthesis and the total carbon content in mature plants. The plants’ macroscopic build-up and lifecycle was considered along with the laboratory results to create a theoretical optimum green roof arrangement for carbon capture. Finally, a computer model was developed using structural data from the university’s city campus to analyse the net predicted carbon sequestration when appropriate infrastructure was converted to the optimal green roofs. This research aimed to reveal which plant species are most suitable for the application to green roofs with regards to carbon capture and henceforth improve existing green infrastructure on the university’s campus. The model’s objective was to showcase the significance of the results in a relevant, real-world application and exhibit the achievable net decrease in carbon emissions to the atmosphere by the University of Bristol. A system of green roofs composed of Lavandula is predicted to capture 4.12kgCO2/m2year, which is the optimal outcome of this research and contrasts with S. Spurium, a common planting on green roofs which is only forecast to capture 0.14kgCO2/m2year. This substantiates the argument that the choice of vegetation plays a crucial role in the performance of the carbon sink active in a green roof. The findings of this study can be replicated for other urban sites and their vegetation choices for their green roofs.