the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Feb 2026
A Global Database of Soil Methane uptake (SMUD)
Abstract. Soil methane uptake (SMU), the second-largest and represents a biologically mediated sink for atmospheric methane (CH4) in terrestrial ecosystems, plays a non-negligible role in regulating the global CH4 budget. Field SMU observations have been conducted since the 1980s, but have not yet been systematically compiled within any unified and openly available framework. Here, we present the global Soil Methane Uptake Database (SMUD), which includes 2427 site-level records from 920 peer-reviewed publications spanning 1986 to 2025. SMUD contains SMU measurements at multiple temporal scales, including daily (n = 1425), monthly (n = 2001), seasonal (n = 1720), and annual (n = 1098), along with soil moisture and temperature data at daily and monthly scales. The collected datasets cover all major climatic zones and ecosystem types, across which SMU exhibits pronounced spatial and temporal variability. We found that seasonal- and biome-specific variations were key to understanding intra-annual changes in SMU. In particular, the effects of soil temperature and moisture on SMU are biome-specific: observations from Temperate Grassland are primarily associated with temperature changes, whereas those from Tropical Rainforest and Desert are mainly controlled by moisture, and other biomes show a mix of controlling factors. Overall, SMUD provides a comprehensive basis for understanding the global patterns of SMU, unraveling the underlying mechanisms, and estimating the global SMU budget. The database, associated data, and code to reproduce the results can be found at https://doi.org/10.5281/zenodo.18299391 (Jiang et al., 2026). We aim to establish SMUD maintenance as a collaborative, community-driven, shared, and user- managed database within the research community.
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Status: open (until 27 May 2026)
- RC1: 'Comment on essd-2026-48', Anonymous Referee #1, 21 Apr 2026 reply
Data sets
CH4 uptake data_CH4 FLUX_1_1410 Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
Studies and Fluxes Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
Studies and Fluxes-unit Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
Model code and software
ch4_conversion_20260118.m Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
sm_conversion_20260118.m Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
st_conversion_20260118.m Jiawei Jiang https://doi.org/10.5281/zenodo.18299391
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- 1
This manuscript presents the Soil Methane Uptake Database (SMUD), a large and valuable compilation of in situ soil CH₄ uptake measurements spanning nearly four decades. The effort to harmonize data from 920 publications into a standardized, open-access database is commendable and highly relevant to the biogeochemistry and Earth system science communities. The inclusion of multi-temporal resolution data (daily to annual) together with associated environmental variables (e.g., soil temperature and moisture) represents a significant advancement over previous datasets.
Overall, the manuscript fits well within the scope of the journal and has strong potential to become a widely used community resource. However, several methodological clarifications, structural improvements, and interpretational constraints should be addressed prior to publication.
The manuscript primarily aims to introduce a database but also includes elements of ecological interpretation (e.g., biome-specific controls and classification into temperature- or moisture-dominated systems). While soil temperature and moisture are indeed key drivers, other factors—such as soil organic matter, pH, and inorganic nitrogen—can be equally or more important depending on spatial scale, biome type, and season. Although incorporating these variables into the database may be beyond the scope of this work, their roles should be more explicitly acknowledged in the Discussion or in a dedicated limitations section.
Line 181: The manuscript states that all fluxes were converted to μg CH4–C m⁻² yr⁻¹, yet subsequent analyses (e.g., in the Results) appear to use μg CH4–C m⁻² h⁻¹. This inconsistency needs clarification. In addition, the authors indicate that only uptake (positive values) was retained, excluding emission fluxes. Given that soils can alternate between CH4 sink and source depending on environmental conditions, this filtering may bias estimates of mean fluxes, seasonal variability, and biome-level comparisons.
The quality control (QC) system (Q01–Q07) is a useful feature; however, it is insufficiently quantified. The manuscript does not report the proportion of data flagged under each category or how exclusions affect the final dataset size. Providing these details would improve transparency and usability.
The dataset shows a strong geographical bias toward the Northern Hemisphere, particularly temperate regions, China, and other countries. While this limitation is acknowledged, its implications are not fully explored. It would be helpful to provide guidance for users, such as potential weighting strategies or cautions when extrapolating to underrepresented regions.
The classification of observations into three categories (temperature-dominated, moisture-dominated, and jointly controlled systems) appears largely qualitative. This framework would benefit from quantitative support (e.g., regression analysis, partial correlation, or mixed-effects modeling). Alternatively, the authors should clearly frame these patterns as descriptive rather than mechanistic.
Minor comments:
Use consistent terminology throughout (e.g., SMU vs. CH₄ uptake vs. CH₄ sink).
Figure 4: The combination of violin, box, and scatter plots reduces visual comparability; consider simplifying the presentation.
Consider including a workflow diagram summarizing the data pipeline (literature search → screening/filtering → data extraction → QC → harmonization).