| 04 Mar 2026
Net ecosystem exchange of extensive green roofs: the role of coupled energy, carbon, and water fluxes quantified by long-term micrometeorological observations
Abstract. Vegetated roofs (i.e. green roofs, GRs) have been emerging as a promising nature-based solution in urban environments to mitigate climate change impacts, such as heat waves, urban flooding, and increased greenhouse gas emissions. Green roofs were shown to provide various ecosystem services, such as carbon sequestration from the urban atmosphere.
The present study leverages a 9-year time series of continuous, integrated flux measurements on a large, extensive GR in Berlin, Germany, using the eddy-covariance technique. We investigate the coupling between carbon, water, and energy fluxes at different temporal scales to determine their role in shaping the net ecosystem exchange (NEE) of the GR ecosystem.
The extensive GR was a moderate carbon sink with an average annual NEE of –92 g C m–2, ranging from –154 to +8 g C m–2 in the study period from 2015–2023. In the final two years, 2022 and 2023, the annual NEE shifted toward net respiration, coinciding with increased nocturnal CO2 efflux and an abrupt rise in substrate organic carbon, which stemmed from external carbon sources. During the study period, the roof retained 51 % of precipitation, with a strong coupling between soil moisture, evapotranspiration, sensible heat flux, and carbon assimilation. Low substrate water content (below ≈ 0.05 m3 m–3) reduced evaporative cooling and suppressed carbon assimilation during the summer.
The findings demonstrate the importance of integrated flux monitoring and emphasise the multifaceted environmental benefits of extensive GRs while also pointing to their structural constraints.
This manuscript about the ability of green roof to act as carbon sink is very important topic. There are available such eddy or chamber investigations from different fields (forests, peatlands) but in some reason there is a lack of such researches about green roofs, which are great opportunity in city environment to improve air quality. Present research is also unique investigation because of its very long period and have therefore clear importance for readers. The text is clear to understand and all findings are correctly explained. All necessary details about measurements and results are given. All my questions are already answered in the article. I am very satisfied with this manuscript. Therefore generally, in my opinion, the present form is acceptable.
When water availability is very low during hot spring and summer, there is lower carbon assimilation by green roof plants. Are there any solutions to a situation where the temperature is ideal but there is no water? One possibility is irrigation but on such a large roof it is complicated. It could be a future topic to investigate whether irrigation helps maintain carbon sequestration efficiency.
As the authors write, there are now solar panels on the roof. Are there any plans to study the interaction between a green roof and panels? The effect of shading from panels on plants?
If you could do a similar large roof survey, what would you do differently? For example, use other plant species besides Sedums.
The formatting and language use throughout the article are correct. No technical errors were found. Also, all references which are used in the text are also showed in the part References.