the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Apr 2026
Methane fluxes from tropical wetlands of the Orinoco River Basin and their regional implications
Abstract. The Llanos del Orinoco, a vast tropical savanna floodplain in northern South America, plays a significant yet understudied role in the global methane (CH4) budget. This study synthesizes existing data to evaluate CH4 emissions from the region, highlighting the interplay between natural processes and anthropogenic influences. Top-down and bottom-up estimates for 2018 reveal annual CH4 emissions ranging from 3.27 ± 0.71 to 5.31 ± 2.50, with wetlands contributing 41–70 % of total fluxes. Seasonal variability follows precipitation patterns, with greater emissions occurring during the rainy season (April–October). However, discrepancies between global biogeochemical models and sparse field measurements underscore significant uncertainties, exacerbated by inconsistencies in inundation mapping and outdated local data. Anthropogenic activities, including oil extraction, livestock farming, and expanding rice cultivation, further modulate CH4 fluxes, though their impacts remain poorly quantified. Historical trends show declining precipitation and increasing temperatures, with models predicting more extreme weather events, potentially reducing wetland extent but favouring CH4 release during remaining inundated periods. Critical research gaps, including the need for updated field measurements, improved inundation mapping, and a better understanding of neglected habitats like peatlands and seasonal wetlands, are discussed. Addressing these gaps is essential for refining global and regional CH4 budgets and developing mitigation strategies. This work calls for integrated monitoring efforts to reconcile model disparities, assess land-use impacts, and predict responses to climate change, ensuring accurate representation of the Llanos del Orinoco in regional and global carbon cycle models.
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Status: open (until 19 Jul 2026)
- RC1: 'Comment on egusphere-2026-2080', Anonymous Referee #1, 22 May 2026 reply
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RC2: 'Comment on egusphere-2026-2080', Anonymous Referee #2, 15 Jun 2026
reply
This is a clear and valuable study highlighting methane emissions from the understudied Llanos del Orinoco region. The topic is important because tropical wetlands are increasingly recognized as a major uncertainty in the global methane budget, and methane emissions in this region may be larger than previously expected. The authors do a great job collecting information from top-down and bottom-up sources and producing quantitative estimates for the region.
My main general comment is that the paper sometimes focuses more on pointing out what is missing than on what is known, even though the authors have done an excellent job collecting and synthesizing the available information. I think the manuscript would be stronger if some sections were smoothed out to first tell a clear story about what is currently known, and then more concisely identify what remains unknown. The message of the paper is important, so I would not want the writing or repetition to detract from it.
In general, the writing could be made smoother and more concise throughout the paper. There is some repeated information, especially around the region being understudied. Again, I feel that this is very important work, and could have greater impact if the writing was made more clear and concise. I provide a few specific suggestions for improving clarity below, starting with the Introduction.
Line 38: “Carbon Dioxide” should not be capitalized.
Line 40: “especially considering potential overshoot scenarios” is a bit vague. I would clarify what you mean here, or make the sentence more specific about why methane is especially important in this context.
Line 43: “approx.” should be changed to “approximately.”
Line 58: “at required spatial and seasonal scales” is unclear. Required by whom, or required for what purpose? Potential to clarify here.
Line 67: “understudied compared to other South American wetlands” repeats the idea already stated at the beginning of the paragraph. Consider removing or shortening this sentence to avoid repetition.
Section 3.1
Lines 161–162: “The small change from prior to posterior in the CAMS-Inversion suggests that the region is not well constrained by the assimilated data.” I think this sentence needs to be clarified. A small prior-to-posterior change could mean the region is not well constrained, but couldn’t it also mean that the CAMS prior is relatively accurate? Could this be diagnosed more quantitatively? For example, what is the observation density for the inversion over this region, or is there any posterior error reduction / sensitivity diagnostic available?
Line 164 and elsewhere: “Wetcharts” should be “WetCHARTs” for consistency with the product name.
Figure 2: Why is the CAMS wetland prior so much higher than the Global Methane Budget wetland fluxes? It could be useful to explain this more clearly in the text.
Section 4
Lines 280–281: “and a lack of coincidence between them” can be omitted because the sentence already says there are large inconsistencies between products.
Lines 283–285: The sentence beginning “Furthermore, there are fundamental differences…” should be clarified. I think the point is important, but the sentence is hard to follow.
Figure 4: This is really interesting. Have you looked at CYGNSS inundation extent as well? CYGNSS could be useful here because it provides satellite-derived, relatively high-resolution information and performs well over tropical regions, including Colombia. It would be great to add if it is not too difficult.
Line 316: “To date, no CH4 emissions data have been recorded from peatlands of the Llanos del Orinoco…” You could clarify this statement since you are using satellite/inversion information over the region to specify that no in situ or peatland-specific flux measurements have been reported.
Line 318: The paragraph beginning “Peatlands that are dependent on rainwater…” is really interesting. This type of mechanistic explanation is very helpful for methane scientists to understand why different wetland types may have different methane emissions. If you have sources to cite here that explain the distinction between rainwater-fed, nutrient-poor peatlands and more minerotrophic/productive peatlands, that would strengthen the paragraph.
Lines 353–354: “Cattle numbers in Colombia have increased by about 25% since 2016…” You could provide a source for this and clarify if this increase is for all of Colombia, or specifically for the Llanos del Orinoco region.
Lines 370–371: “Nathan et al. (2024) estimate national emissions for Venezuela of 7.5 Tg CH4 yr-1 in 2019, which is higher than our regional estimate for the entire Llanos del Orinoco.” I do not fully understand the point of this comparison, because presumably total Venezuelan emissions would be higher than emissions from only the Llanos del Orinoco. I would either clarify what this comparison is meant to show or replace it with a more direct comparison.
More generally, are there other broader TROPOMI regional studies that could be used to provide more top-down data for comparison? Other studies show some seasonal coverage over parts of the Orinoco region. Even if the satellite coverage is limited by clouds or surface conditions, it could be useful to include additional regional top-down context.
Overall, I appreciate the attention this paper brings to the Llanos del Orinoco, which is clearly an important and understudied region for the methane budget. Quantifying the wetland contribution here is especially important given the large differences among existing estimates and the uncertainty in inundation extent. I think the manuscript makes a valuable contribution by bringing together the available data, and I recommend publication after revisions that improve the flow, reduce repetition, and clarify a few points.
Citation: https://doi.org/10.5194/egusphere-2026-2080-RC2 -
RC3: 'Comment on egusphere-2026-2080', Anonymous Referee #3, 22 Jun 2026
reply
The work seems interesting based upon Abstract and Introduction, but it is presented as “this is what we are doing, and why we are doing in this way has not been provided”. As an academic work, providing the rationale of "why we are doing/selecting/developing this, rather than that..." is more important than "we are doing...". This is shown from data selection to methodology design. No detailed information of each selected data source, the function of each data source, spatial and temporal resolution and coverage, and rationale of data selection; no rationale of methodology/model selection, and temporal resolution of the model outputs, even no description of the listed two equations on page 5, and nothing in methodology is provided how to separate the wetland fluxes from others, and no validation of the model outputs. what is the benchmark of the estimations? Because of this, we cannot tell whether the estimations are correct or not. Figure 1 has not been called out in text and corresponding text has not been included. No real field data used to validate the estimations, even no reference dataset to validate the extent of wetlands in such a big area. Uncertainty might be huge because of no such dataset with detail level to quantify the heterogeneity of inundation frequency, wetland extent, and others.
Citation: https://doi.org/10.5194/egusphere-2026-2080-RC3
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- 1
Methane emissions from the tropics play a significant role in the global methane cycle. While the Llanos del Orinoco represents a vast tropical savanna floodplain in northern South America, the sources, sinks, and processes driving regional methane dynamics remain understudied.
In this manuscript, the authors integrate top-down atmospheric inversion estimates (CAMS) and bottom-up process-based modeling (WetCHARTs, GCP-CH₄), together with a systematic compilation of sparse field measurements, to quantify regional CH₄ emissions and identify key uncertainties.
Overall, the manuscript is valuable and has the potential to advance our understanding of methane cycling and its uncertainty sources in the tropical Llanos del Orinoco region. I would recommend this manuscript for publication after addressing the following comments, which mainly relate to methodological clarification, uncertainties, and interpretation of results.
Main comments
“Databases associated with lakes and wetlands were analyzed at 1 km resolution”: Could the authors clarify the temporal resolution of each dataset used? In addition, more recent datasets are now available and could improve the analysis or could be discussed:
GLWD v2: Lehner et al. (2024). Mapping the world’s inland surface waters: an update to the Global Lakes and Wetlands Database (GLWD v2). Earth System Science Data.
GIEMS-MethaneCentric: Bernard et al. (2024). The GIEMS-MethaneCentric database: a dynamic and comprehensive global product of methane-emitting aquatic areas. Earth System Science Data.
2. Bottom-up and top-down models used: 1) It appears that only one top-down product (CAMS) was used. How are uncertainties across different top-down inversion systems accounted for? 2) For bottom-up estimates, the analysis seems to focus primarily on wetland CH₄ models. How are uncertainties from other sectors (e.g., lakes, rivers, livestock, oil and gas, soil uptake) incorporated? 3) For the GCP-CH₄ dataset, which specific models, and sectors were used in the analysis?
Minor comments