the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 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.
Competing interests: The contact author has declared that neither of the authors has any competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(3006 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3006 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2026-942', Anonymous Referee #1, 20 Mar 2026
- AC1: 'Reply on RC1', Niklas Markolf, 30 Apr 2026
-
RC2: 'Comment on egusphere-2026-942', Anonymous Referee #2, 14 Apr 2026
The manuscript is examining coupled energy, water and carbon fluxes over an extensive green roof for a 9-year period. As such, the dataset is interesting, but the current challenge of the manuscript is the large overlap with earlier paper from the same roof (Konopka et al. 2021) reporting the first 5-years of the same 9-year measurement period. Already there, it was shown how the integral turbulence statistics look good as well as it included a detailed footprint evaluation of the EC system. The same paper also examined in detail the seasonal and year-to-year variability of carbon fluxes and evapotranspiration (and Bowen ratio), and the dependency of the carbon fluxes on environmental conditions. It appears that the only new outcome of the present paper is that in 2022-2023 the green roof acted as a source for carbon due to higher amount of soil organic carbon (SOC). This was explained in a lengthy way in the manuscript as it is kind of self-evident that such high respiration rates can only relate to increased amount of SOC in the soils. What is more interesting is that the green roof carbon fluxes are so sensitive to additional carbon in the system making them very sensitive for any management practice. Furthermore, many of the reported results were self-evident such that the fluxes have seasonal and diurnal variability, or that they depend on environmental variables. The language of the manuscript would need to be improved as past/present tenses were used and the authors talked eg of nocturnal respiration whereas there is no such thing but rather vegetation and soil respire also in daytime but this is masked by the photosynthesis. Finally, the authors do not compare the calculated energy, water and carbon fluxes to other urban green areas types such as lawns, parks, forests and trees so that there would be understanding how the green roof compares with other urban green area types in cooling and uptaking carbon.
For the manuscript to be published in Biogeosciences, the authors would need to clearly bring new information on the coupled fluxes of water, heat and carbon, something that the earlier work from the same roof would not have reported. Until this, the manuscript appears as a simple report without new knowledge to the scientific community.
Citation: https://doi.org/10.5194/egusphere-2026-942-RC2 - AC2: 'Reply on RC2', Niklas Markolf, 30 Apr 2026
Peer review completion
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2026-942', Anonymous Referee #1, 20 Mar 2026
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. Â
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.
Citation: https://doi.org/10.5194/egusphere-2026-942-RC1 - AC1: 'Reply on RC1', Niklas Markolf, 30 Apr 2026
-
RC2: 'Comment on egusphere-2026-942', Anonymous Referee #2, 14 Apr 2026
The manuscript is examining coupled energy, water and carbon fluxes over an extensive green roof for a 9-year period. As such, the dataset is interesting, but the current challenge of the manuscript is the large overlap with earlier paper from the same roof (Konopka et al. 2021) reporting the first 5-years of the same 9-year measurement period. Already there, it was shown how the integral turbulence statistics look good as well as it included a detailed footprint evaluation of the EC system. The same paper also examined in detail the seasonal and year-to-year variability of carbon fluxes and evapotranspiration (and Bowen ratio), and the dependency of the carbon fluxes on environmental conditions. It appears that the only new outcome of the present paper is that in 2022-2023 the green roof acted as a source for carbon due to higher amount of soil organic carbon (SOC). This was explained in a lengthy way in the manuscript as it is kind of self-evident that such high respiration rates can only relate to increased amount of SOC in the soils. What is more interesting is that the green roof carbon fluxes are so sensitive to additional carbon in the system making them very sensitive for any management practice. Furthermore, many of the reported results were self-evident such that the fluxes have seasonal and diurnal variability, or that they depend on environmental variables. The language of the manuscript would need to be improved as past/present tenses were used and the authors talked eg of nocturnal respiration whereas there is no such thing but rather vegetation and soil respire also in daytime but this is masked by the photosynthesis. Finally, the authors do not compare the calculated energy, water and carbon fluxes to other urban green areas types such as lawns, parks, forests and trees so that there would be understanding how the green roof compares with other urban green area types in cooling and uptaking carbon.
For the manuscript to be published in Biogeosciences, the authors would need to clearly bring new information on the coupled fluxes of water, heat and carbon, something that the earlier work from the same roof would not have reported. Until this, the manuscript appears as a simple report without new knowledge to the scientific community.
Citation: https://doi.org/10.5194/egusphere-2026-942-RC2 - AC2: 'Reply on RC2', Niklas Markolf, 30 Apr 2026
Peer review completion
Journal article(s) based on this preprint
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 744 | 283 | 103 | 1,130 | 61 | 102 |
- HTML: 744
- PDF: 283
- XML: 103
- Total: 1,130
- BibTeX: 61
- EndNote: 102
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Niklas Markolf
Stephan Weber
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3006 KB) - Metadata XML
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. Â
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.