Modelling extensive green roof CO2 exchanges in the Town Energy Balance urban canopy model

Abstract

Green roofs are promoted to provide ecosystem services and to mitigate climate change in urban areas. This is largely due to their supposed benefits for biodiversity, rainwater management, evaporative cooling, and carbon sequestration. One scientific challenge is quantifying the various contributions of green roofs using reliable methods. In this context, the green roof module already running in the Town Energy Balance urban canopy model for water and energy exchanges was improved by implementing CO2 fluxes and carbon sequestration potential. This parameterization combines the Interactions between Soil-Biosphere-Atmosphere (ISBA) photosynthesis, biomass, and soil respiration module with the green roof module in order to quantify the net CO2 amount emitted or fixed by the green roof over a time period. Measurement data from an extensive non-irrigated Sedum green roof located at Berlin Brandenburg (BER) Airport in Germany from 2016 to 2020 are used to calibrate and evaluate the parameterization. Based on the 5 years of measurements, a sensitivity analysis is conducted to quantify the significance of selected parameterization parameters for the photosynthesis process, followed by a calibration over the most important parameters and an evaluation. Results show good agreement of the simulated leaf area index and CO2 fluxes with in situ observations, with good diurnal, seasonal, and inter-Annual variability, although the model tends to be overly responsive on the day-To-day variability. The model effectively reproduces net ecosystem exchange, which provides a reliable estimation of the annual carbon sequestration. These results are encouraging in terms of quantifying the potential of carbon sequestration by green roofs and open up the possibility of applying the new parameterization on a city-wide scale to evaluate green roof scenarios. Copyright: