Introduction

AmeriFlux is a network of research sites and scientists that use the eddy-covariance technique to measure ecosystem carbon, water, energy, and momentum fluxes in ecosystems across the Americas1. It was established in 1996 to connect independently-managed research in these diverse ecosystems, thus jointly representing major climatic and ecological contexts. Over the last few decades, AmeriFlux has been at the forefront of land-atmosphere interaction research, committed to collecting and sharing high-quality flux and meteorological (flux-met) data among the community of flux researchers. This broader AmeriFlux community of both site teams and data users contributes to science in many ways, including fundamental research, Earth system model development, data science, technical innovation, and science education. For example, AmeriFlux data are widely used to benchmark, validate, and develop new algorithms in the land models of Earth system models2,3. Remote-sensing scientists use AmeriFlux data to parameterize and validate models to upscale carbon and water fluxes in space and time4,5,6. The biogeochemistry and ecology communities use AmeriFlux data to construct budgets of elements with high precision and sampling frequency7,8,9 and identify new and emerging processes, such as the divergence/convergence of ecosystem functions (e.g., carbon uptake, water use, carbon use, energy partition) across space and time10,11,12,13. Long-term AmeriFlux data are valuable in assessing ecosystem carbon sequestration, water and energy budget, and response to climate change, disturbances, management practices, and climatic extremes14,15,16,17. The impact of research based on AmeriFlux data goes beyond these examples and continues to grow, integrating processes across disciplines and spatiotemporal scales.

Since its launch in 1996, AmeriFlux has grown from 15 sites to >110 in 2012 when the AmeriFlux Management Project (AMP, see below) was established, and to 590 sites at the end of 2022 (Fig. 1). These sites represent a broad spectrum of ecosystems across climatic and ecological gradients and diverse regimes of natural disturbance and human management (Fig. 1, Supplementary Figure S1). AmeriFlux is distinguished among all flux networks by having more than 100 sites with times series longer than a decade, including several of the longest-running sites in the world (e.g., Harvard Forest (US-Ha1, 1991-current), Borden Forest (CA-Cbo, 1994-current), Park Falls (US-PFa, 1995-current), Howland Forest (US-Ho1, 1995-current)). These long flux records allow scientists to address questions requiring decades of observations18, such as understanding ecosystem response to climate variability and atmospheric change14,15,19,20. AmeriFlux also contains many clusters of neighboring sites established by individual research groups21. Driven by research questions, many site clusters were established across gradients of land cover and land use, chronosequence stages, microclimate, management, disturbance, and restoration22,23,24,25. The site clusters enable the research communities to understand how different ecosystems respond to similar climatic and, in some cases, edaphic conditions. Moreover, measurements across wide environmental gradients can be constructed from the network’s sites at a regional or continental scale. This distinctive cluster/gradient design makes AmeriFlux data a powerful testbed for model benchmarking, assessing the effects of climate and land cover and land use changes26,27.

Fig. 1
figure 1

Map of AmeriFlux sites. Triangles represent registered sites (146) with no available data, and circles represent sites (444) with data available through AmeriFlux. The circles’ size indicates the length of the data record. The color of the circles represents the ecosystem type based on the International Geosphere-Biosphere Programme (IGBP) definition. Parentheses indicate the number of sites in each data availability and IGBP group. The inset shows the cumulative number of registered sites over the years. All numbers are updated as of the end of 2022.

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AmeriFlux’s wide diversity of ecosystems, instruments, data-processing routines, and science activities are both its strength and challenge. AmeriFlux sites are established by individual site teams driven by diverse research needs and questions1. As a result, research designs and measurements vary among sites, being tailored to each ecosystem and project. This individuality distinguishes AmeriFlux from other flux networks, such as the National Ecological Observatory Network (NEON) and Integrated Carbon Observation System (ICOS28), which have standardized instrument packages and data-processing protocols29,30,31,32,33. AmeriFlux’s diverse and innovative nature has enabled the network to evolve and adapt to new technology when available (and promote that evolution)34,35,36,37. However, the diversity in approaches also challenges data standardization, quality assurance, and data sharing across the network.

In 2012, the United States Department of Energy (DOE) established AMP at the Lawrence Berkeley National Lab (LBNL) to support the broader AmeriFlux community, composed of the AmeriFlux site teams that produce flux-met data and the researchers who use these data. AMP collaborates with AmeriFlux researchers to ensure the quality and availability of the continuous, long-term measurements necessary to understand ecosystems and to build effective models and multisite syntheses. To achieve these goals, AMP has established technical, data, and outreach services, held annual meetings and workshops, and provided operational support to 13–14 flux site clusters (Core sites) to ensure public access to high-quality and long-term flux-met datasets. AMP further supports the community by creating new opportunities (e.g., AmeriFlux Annual Meetings, theme years, working groups, synthesis workshops, webinars) for AmeriFlux researchers to contribute to high-impact research.

AMP’s data support centers on developing standards, data QA/QC, data-processing, and data repositories. AMP worked collaboratively with international partners, particularly ICOS, to design and develop standard formats and processing routines. In 2017, the AMP team at LBNL took full responsibility for the AmeriFlux data repository, previously maintained by the Carbon Dioxide Information Analysis Center (CDIAC) at the Oak Ridge National Lab (ORNL). With that, AMP redesigned, implemented, and launched the new BASE data-processing pipeline (details below), with the objectives of (1) standardizing the flux-met data formats, (2) ensuring and improving the data quality, (3) facilitating regular and frequent data submissions and publications, and (4) tracking the data and communications with site teams through the pipeline. The following sections summarize the outcome of the data-processing pipeline. The methodology behind its design and implementation are detailed in the Methods.

Results

The BASE data-processing pipeline begins with site teams submitting their flux-met data in a standardized format, followed by a series of quality assurance and quality control (QA/QC) checks performed by AMP, e.g., Format QA/QC for format compliance and Data QA/QC for data quality (Fig. 2). AMP then communicates the check results and, if any, needed corrections with site teams through Format and Data QA/QC reports. Once passing QA/QC checks, the flux-met data are published as the BASE data product for each site, i.e., made publicly available on the AmeriFlux website. The BASE data format follows an international standard compatible with other flux networks like ICOS and European Database.

Fig. 2
figure 2

AmeriFlux BASE data-processing pipeline. The pipeline begins with data uploads from the site teams, followed by steps of Format QA/QC, Data QA/QC, and BASE Publish performed by AmeriFlux Management Project (AMP). The end products are the flux/met data (BASE) and Biological, Ancillary, Disturbance, and Metadata (BADM) products. Green, brown, and blue colors in the figure represent actions taken by site teams, AMP, and data users, respectively. While not detailed in this article, the BASE and BADM products can be used as input to the FLUXNET processing pipeline42.

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Data upload and release

Between implementing the pipeline in May 2017 and December 31, 2022, we have received 3,468 data uploads containing 6,195 files of flux-met data from 385 sites (Fig. 3a). AMP generated 3,538 Format QA/QC and 1,980 Data QA/QC reports that were emailed to site teams (Fig. 3b). Notably, in 2020–2022, we received data uploads from ~200 sites each year and sent more than 600 and 400 Format and Data QA/QC reports yearly. As a reference, the BASE data repository contained 1,256 site-years of data from 174 sites in April 2017. The 2017–2022 period coincided with the rapid growth of the network (Fig. 1). The implemented pipeline enables us to keep up with the growth, publishing on average ~48 new sites and ~330 new site years each year. As of 2022, there are 3,130 site years of AmeriFlux BASE data from 444 sites, representing the world’s largest data repository for flux-met data. Moreover, 344 sites (~77%) are under the CC-BY-4.0 license.

Fig. 3
figure 3

Records of data uploads, QA/QC reviews, and data published. Light- and dark-gray bars in Figure (a) show the number of sites uploading and publishing data each year since 2013. Gray circles show the cumulative number of sites publishing data since 2013. Light- and dark-gray bars in Figure (b) show the number of Format and Data QA/QC reports since implementing the BASE data-processing pipeline in 2017. All numbers are updated as of the end of 2022.

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During 2017–2022, 288 sites submitted data for the first time and were checked by the Format and Data QA/QC. Around 94% of these new sites’ data was published in the BASE data product as of 2022. For each site’s first complete publishing cycle, these new sites took a median of 127 days from the first-time data upload to BASE publication. The durations varied depending on the number of iterations required to resolve the identified issues, particularly in the Data QA/QC. While varied among sites, common data issues include shifts in timestamps, sensor degradation, excessive outlier, incorrect units, and flipped sign conventions. About 29%, 33%, and 28% of sites went through 1–3 (re)submission cycles, with median durations of 60, 116, and 154 days, respectively. This latency time, especially for the new sites, is reflected in the difference between the number of sites uploading and publishing data within each year (Fig. 3a).

Around 217 sites updated their BASE data product (e.g., adding additional years of data to previously published BASE) in 2017–2022, including 150 new sites discussed above. The median turnaround duration was around 42 days from upload to BASE publication, much shorter than the first-time submissions from the new sites. Most (80%) of these returning sites took less than 90 days from the upload to BASE publication. Seventy-five sites updated their BASE data product more than five times in 2017–2022.

In sum, the BASE pipeline facilitates more frequent data uploads and releases and allows data users to access recent-year data. While traversing the pipeline entailed a few iterations and months for new sites to address the identified issues, it significantly decreased the overall latency time between data collection and release for many returning sites. For example, the number of sites with data available for the prior year increased from 0 sites in 2017 to 90 sites in 2022 (Supplementary Figure S2). Over 2017–2022, the BASE data products were downloaded more than 27,000 times by ~4,800 users globally. Many of these downloads included multiple sites, resulting in total site downloads of 318,553 for the period. Notably, the total site downloads increased from 18,644 in 2017 to 86,371 in 2022. The data-download interface logs the downloader’s intended data use, and these covered a wide range38, such as multisite synthesis, benchmarking remote-sensing and land surface models, and education.

Data summary

The BASE data pipeline generates the BASE data product: time series flux-met data at a half-hourly or hourly resolution. The BASE data product follows the global FP (Flux Processing) Standard39, ensuring that variable names, units, and file formats are defined and consistent. Around 52 out of 143 variables supported by the FP Standard are commonly submitted (>50 sites, Fig. 4, Supplementary Table S1). These variables can be categorized into flux-related groups, such as the trace gasses (e.g., CO2 and CH4 fluxes and concentrations), energy (e.g., latent and sensible heat fluxes), derived products (e.g., gross primary production, ecosystem respiration), quality flags (e.g., steady-state and integral turbulence characteristics), and footprints (e.g., distance with maximum footprint contribution). The BASE data product also consists of data on meteorology and soil, such as the groups of radiation (e.g., net radiation, incoming shortwave radiation), atmosphere (e.g., air temperature, relative humidity), wind (e.g., friction velocity, wind speed), precipitation, and soil (e.g., soil temperature, soil water content). It is worth mentioning that some sites have data measured at multiple locations (dark colors in Fig. 4) for replication or spatial variation. In particular, soil temperature and water content are measured extensively in vertical or horizontal locations at most sites. Air temperature, wind speed, direction, CO2 and H2O concentrations, and soil heat fluxes are also measured at multiple locations at around 80–120 sites.

Fig. 4
figure 4

BASE data variable availability by variable types. Bars indicate the numbers (left y-axis) and percentages (right y-axis) of sites. Annotated texts denote the variable names. The colors of the bars indicate the number of unique variables (e.g., locations, sensors) at a site. The figure only contains the most commonly available variables (i.e., >50 sites). Variable definitions and units refer to Supplementary Table S1. All numbers are updated as of the end of 2022.

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BASE flux-met data are rich time series, typically with half-hour resolutions and data records that span from years to decades. While a portion of sites (<50) started in the 1990s, most sites’ data records were concentrated in 2004–2020, with around 140 sites operating concurrently (Supplementary Figure S2). Figure 5 illustrates the temporal characteristics of selected flux data across AmeriFlux sites, highlighting a few long-running sites (red lines in left panels and time series in right panels). Most flux data show evident temporal variation at the sub-daily to daily and seasonal to annual scales, reflecting biological (e.g., phenology) and climatic regulation (Fig. 5a,c,e,g,i). Yet, distinct temporal variations were observed across sites depending on the temporal scales. For example, CH4 fluxes (FCH4) show weak to negligible seasonality at some but not all sites (Fig. 5i). And no consistent temporal variation was observed for all flux variables on weekly to monthly scales. With more than 100 sites now having decade-long records, it becomes feasible to explore the temporal characteristics at a longer scale. While some sites reveal weak variability near the quinquennial scale, we did not find a general pattern across sites.

Fig. 5
figure 5

Wavelet power spectra (left panel) and time series (right panel) of flux variables. From top to bottom, the variables are (a,b) friction velocity (USTAR), (c,d) sensible heat flux (H), (e,f) latent heat flux (LE), (g,h) CO2 flux (FC), and (i,j) CH4 flux (FCH4). Each gray line in the left panel represents a power spectrum from an AmeriFlux site, including all sites under the CC-BY-4.0 data license and with >25% of data coverage. The red lines highlight the power spectra from the selected long-term sites, annotated with their site ID. The right panel shows the time series of flux variables from the selected long-term sites. Wavelet power was presented in logarithmic scales (left y-axis) and rectified to eliminate bias to allow comparisons among the periods69. All numbers are updated as of the end of 2022. See Table 1 for a complete list of sites and Supplementary Table S2 for their data years and citations.

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Discussion

Network growth and data sharing

Since its onset, AMP has engaged with the AmeriFlux community, both the site teams and data users, through services centered on data, technique, and outreach. During this period, AMP supported and facilitated the growth of the AmeriFlux network, reflected in the rapid increase in registered sites, available data, and data usage (Figs. 1, 3, Supplementary Figure S2).

Since the network’s conception, data sharing has been a core tenet of AmeriFlux. AMP strives to maintain this practice, focusing on the dual goals of increasing the number of site teams contributing data and improving the quality and quantity of the data available. Key to this approach is semi-automation in the BASE data-processing pipeline, which has led to dramatic improvements in the breadth of QA/QC checks performed and the consistency of a high-quality BASE data product. Additionally, the BASE data-processing pipeline reduces the turnaround time that site teams receive feedback from 6–12 to 1–2 months, enabling more rapid data correction. While the QA/QC checks may present a hurdle for new site teams submitting their data for the first time, the independent data quality assessment by AMP is a key benefit of joining the network. And once the site teams became familiar with the QA/QC processes, the time from submission to publication was significantly reduced. Overall, the pipeline decreased the latency time from data collection to release. The addition of a CC-BY-4.0 data policy adopted by a majority of the network has significantly improved the findability, accessibility, interoperability, and reusability of the data.

Synthesis and extended products

The AmeriFlux BASE data product’s life cycle continues after its release, further enabling and facilitating numerous data products and syntheses. For example, the FLUXNET data products—a gap-filled data product with value-added variables (i.e., partitioned gross primary productivity)—are part of global datasets used for model validation and benchmarking for decades40,41. In this regard, AMP collaborates with international partners like ICOS to develop the ONEFlux (Open Network-Enabled Flux) codes, fostering the creation of the FLUXNET2015 data product42. Furthermore, AMP is leveraging the high-quality standardized BASE data product as input to the ONEFlux codes to produce the next-generation FLUXNET data product for AmeriFlux sites. Additionally, the infrastructure and workflows developed for the BASE data-processing pipeline are being extended to produce the FLUXNET product (Fig. 2). As of 2022, AMP released the new AmeriFlux FLUXNET data product for 79 AmeriFlux sites. AMP anticipates continuing to release and update the AmeriFlux FLUXNET data products in coordination with other flux network partners43. The FLUXNET-CH4 community data product demonstrates another example of an extended product based on the BASE data product44,45. Among 81 sites included in the FLUXNET-CH4 data product, 45 are AmeriFlux sites that make their data available through the BASE data product.

AmeriFlux BASE data also facilitate syntheses that utilize data from multiple sites, a unique tool for scientific discovery. Recent examples include fundamental research13,46,47,48, model evaluation and benchmarking49,50, remote-sensing validation51,52,53,54, machine learning55,56, and science education57.

Future direction of the data pipeline

The AmeriFlux BASE data-processing pipeline design considers the network’s unique aspects, such as distributed site teams, diverse instrumentation and processing routines, which distinguishes it from those implemented by other flux networks30,31,58,59. The data-processing pipeline incorporates many features (e.g., visualization, QA/QC report summaries, central communication tracking) to facilitate interactions with individual site teams. While the Format QA/QC assessment was fully automated earlier in the pipeline development, the Data QA/QC assessment remains a semi-automated process. The Data QA/QC module automatically generates statistics and figures, and AMP team members evaluate results and synthesize identified issues into a concise, readable, and actionable report. Full automation is challenging to achieve. For example, a single data issue can trigger warnings in multiple QA/QC checks. Thus, identifying and interpreting the root cause can be non-trivial. Without a concise report, the figures and statistics alone are difficult for data providers (particularly new site teams) to interpret and take appropriate action. At the same time, manual review by AMP is unsustainable, given the expected network and data-submission growth. Further development on fully automatic and self-interpretable Data QA/QC reports and training for site teams is in progress to further reduce the turnaround time and keep pace with the network growth and continuous data updates.

While most AmeriFlux sites’ data concentrated on about 60 common variables (e.g., fluxes, radiation, meteorology, soil, Fig. 4), research innovation has promoted the discussion of new variables and/or metadata. We partner with the AmeriFlux community members and other networks to develop new variables and their corresponding metadata and data check and processing routines. For example, to support the activities in the Year of Methane in 2018–2019, we worked with the Global Carbon Project, FLUXNET, and ICOS to add new aquatic variables (e.g., water temperature, dissolved oxygen) to the FP Standard. Most recently, the Year of Remote Sensing also facilitated the addition of new tower-based spectral variables, e.g., Near Infrared Vegetation Index60. The pipeline is designed to seamlessly support these new types of continuous measurements as they are added to the FP Standard. If new variables require additional quality assessments, the Data QA/QC module can be easily extended due to its modular design.

Methods

Data collection and processing at individual sites

AmeriFlux flux-met data’s life cycle begins with data collection at each field site using a suite of automated instruments. The instruments may vary from site to site but include eddy-covariance instruments (i.e., sonic anemometer, gas analyzer) and a selected set of meteorological, soil, and biological sensors. The data streams are recorded continuously (e.g., 10–20 Hz for flux measurements, 1-0.1 Hz or slower for others) by the data acquisition systems (e.g., logger, computer) and retrieved via physical visits or remote connection (e.g., cellular modem, radio transfer, Ethernet, satellite). Next, the site teams apply quality control and process the high-frequency data using selected software or in-house codes to produce flux-met data at a half-hourly or hourly resolution. Previous comparison studies showed that software selection generally led to marginal differences29,61,62,63 although the differences in the corrections implemented could also lead to systematic biases (e.g., spectral corrections function of air humidity64). Yet, the selection of corrections applied in the flux calculation (e.g., coordinate rotation, despiking, time lag optimization, spectral corrections), judged and augmented by individual researchers, can vary among sites based on sites’ characteristics (e.g., climate, canopy heights, tower structures, instrument types, and setup). Last, the data are checked and filtered by the site teams before uploading to the AmeriFlux website. Gap-filling is not required, but gap-filled variables can be provided in addition to non-filled ones.

AmeriFlux BASE data-processing pipeline

The goal of the AmeriFlux BASE data-processing pipeline is to provide high-quality flux-met data in a standardized format that enables a broad range of Earth science research and educational activities. Our approach requires site teams to process high-frequency observations into half-hour or hourly fluxes (described above), prepare them in a standardized format (details below), and then submit these data to the AmeriFlux website. Upon submission, our semi-automated BASE processing pipeline is initiated and performs QA/QC checks (Fig. 2). If the submitted data pass the QA/QC checks, the resulting BASE data product is published, i.e., made publicly available on the AmeriFlux website. All data uploads are logged, all communications are tracked, and the data provenance is maintained.

The BASE processing pipeline consists of 3 modular components: Format QA/QC, Data QA/QC, and BASE Publish (Fig. 2). The automated portions of the pipeline are primarily written in Python (see Code Availability for the code repository). The pipeline logs the processing status of all data submissions and published BASE data products in a SQL database. All detected data issues and communication between the site team and AMP are recorded in information technology JIRA Service Management.

The Format QA/QC module assesses compliance of submitted data files with the AmeriFlux FP-In (Flux Processing In) standardized format65. It makes one attempt to automatically correct minor issues if discovered (Fig. 6). The site teams receive a Format QA/QC report within a few hours after submission (Supplementary Figure S3). The FP-In format follows the timestamp, variable name, units, and data formatting conventions of the global FP (Flux Processing) format, namely a comma-delimited file with variables in columns at a timestep of half-hour or an hour in rows. The minimum variables required are the start and end timestamps and one carbon flux observation (FC or FCH4). However, most site teams also submit gas concentrations, gas and energy fluxes, basic meteorological observations (e.g., air temperature, wind speed and direction), and radiation observations. In requiring the FP-In format, the automated pipeline code can attempt fully automatic correction of various minor errors, including filling the skipped time intervals with the missing value designator −9999, fixing incorrect variable names, changing the file format to CSV, etc. Site teams can submit a site’s full data record, replacement data for previously submitted data, or new data that extend the site’s record.

Fig. 6
figure 6

Format QA/QC workflow. Once a flux-met file is uploaded, the Format QA/QC module is automatically executed to assess format compliance with the required AmeriFlux FP-In format. A single autocorrection attempt is made if format issues are found (1 in the figure). An automated email is sent to the uploader that indicates the overall status (2), site team action, and links to Format QA/QC Reports detailing any format issues. The figure is adapted from Faybishenko et al.70.

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The Data QA/QC module assesses the quality of flux-met data uploaded to AmeriFlux. It is a secondary data quality assessment that is independent of and complementary to the data quality checks performed by site teams prior to upload. The Data QA/QC follows a similar methodology to the FLUXNET2015 dataset42,66 but includes additional checks based on data user feedback (e.g., emails, workshops). Also, its design considers the long history of AmeriFlux data repositories and the diverse ecosystems and climates of AmeriFlux sites. For example, specific checks were developed to detect spurious trends and shifts in long-term records. Site-specific plausible ranges were constructed for each site to accommodate the wide range of climatic and ecosystem conditions. Last, the Data QA/QC uses data visualization and a ticket-tracking system (i.e., JIRA Service Management) to facilitate communication with site teams. Six Data QA/QC check modules are implemented currently: timestamp alignment, physical range, multivariate comparison, diurnal-seasonal pattern, USTAR filtering, and variable coverage (Table 2). Details and example figures of each module are provided in Supplementary Materials (Supplementary Text S1, Supplementary Figures S4-S17). AMP also hosts workshops and webinars for site teams to learn about the QA/QC (recordings available at https://ameriflux.lbl.gov/community/amp-webinar-series/).

Table 1 A list of the AmeriFlux site ID (316) used in the wavelet power spectra analyses.
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Table 2 Summary of the target issues for each Data QA/QC module.
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Once passing Format QA/QC, the uploaded files are combined with a site’s previously published BASE data product to form a complete data record (Fig. 7). Data QA/QC modules are executed and automatically generate figures and summary statistics (e.g., Supplementary Figure S18). The module execution time is typically within a few hours for a site’s data. Then, AMP conducts Data QA/QC reviews of sites in batches ranging from weekly to monthly and synthesizes the identified issues into a concise, actionable report (e.g., Supplementary Figure S19). While varying among cases, the average time for Data QA/QC review is typically less than an hour for each site. The report also explains the background of Data QA/QC and provides links to all summary statistics and figures generated. If there are identified issues, AMP notifies the site team of corrections needed. Otherwise, the data are queued for BASE data publication.

Fig. 7
figure 7

Data QA/QC workflow. After passing Format QA/QC, uploaded files are combined with, if any, previously published BASE files (1). The automated Data QA/QC codes generate statistics and figures that AMP reviews (2). If the data trigger any potential issues, AMP notifies the site team of corrections needed (3). Otherwise, the data are queued for BASE generation and bundled with BADM for publication (4).

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The BASE Publish module occurs after data pass the Data QA/QC, typically in batches once every 1–2 months for both new sites publishing for the first time and returning sites updating data. AMP formats the flux-met data in the FP Standard format, bundles them with Biological, Ancillary, Disturbance, and Metadata (BADM, details below), and versions the bundled data. In addition, the module obtains Digital Object Identifier (DOI) for new data and updates metadata for existing DOIs before making the BASE data product available on the AmeriFlux website. The BASE data product is organized by sites, with one zipped file containing both BASE and BADM data of an AmeriFlux site. Details of the file format and structure are provided in Supplementary Text S2.

In addition to data search and download access, the AmeriFlux website also supports a suite of web-based features for showing each site’s general information, data citation, download logs, images, publications, and related data (e.g., prevailing wind visualizations). Each site with published BASE data that has been assigned a DOI can edit its contributor lists. Last, external links to the sites’ cut-outs of remote-sensing and gridded products, such as MODIS, VIIRS, ECOSTRESS, and Daymet, are also provided through collaborative agreements with Distributed Active Archive Center (DAAC) at ORNL. See Supplementary Text S3 for a quick guide for BASE data use.

BASE data policy

Starting in Fall 2021, AMP worked with AmeriFlux site teams to adopt the new AmeriFlux CC-BY-4.0 Data Use License, which allows data to be shared under the widely-used Creative Commons BY 4.0 license (CC-BY-4.0). As of the end of 2022, 406 AmeriFlux sites (~69% of registered sites) have adopted the CC-BY-4.0 Data Use License. Among 444 sites with BASE data, 344 sites (~77%) are under the CC-BY-4.0 license. The CC-BY-4.0 license makes AmeriFlux data more compatible with other flux networks (e.g., ICOS, OzFlux, and NEON) and more consistent with the FAIR (Findable, Accessible, Interoperable, and Reusable) principle of accessibility, which is now widely encouraged or required by many journal publishers and funding agencies.

Relevant metadata supporting base data

Biological, Ancillary, Disturbance, and Metadata (BADM) are non-continuous information that characterizes a site and complements the BASE flux-met data. BADM includes general site descriptions, metadata about the instruments, maintenance and disturbance events, and biological and ecological data67. See the AmeriFlux website for a complete and updated list of all BADM groups and variables68.

To support AmeriFlux BASE data use, AMP developed and released multiple new BADM sets, including the Measurement Height data, which provides information on BASE data measurement heights/depths and instrument models. The Measurement Height information is provided directly by the site teams or pulled by AMP from historical records and is updated in conjunction with the BASE Publish schedule.