Abstract
Abstract. Drainage of large areas with organic soils was conducted over the past century to free up land for agriculture. A significant acceleration of such trends was observed in recent decades in Southeast Asia, largely driven by drainage of tropical peatlands, an important category of organic soils, for cultivation of oil palm. This work presents the methods and main results of a new methodology developed for FAOSTAT, whereby the overlay of dynamic maps of land cover and the use of information about histosols allows the production of a global annual dataset of drained area and emissions over a time series, covering the period 1990–2019. This is an improvement over the existing FAO approach, which had produced only a static map of drained organic soils for the year 2000. Results indicate that drained area and emissions increased by 13 % globally since 1990, reaching 24 million hectares in 2019 of drained organic soils, with world total emissions of 830 Mt of carbon dioxide (CO2) equivalent. Of these totals, the largest contribution was from the drainage of tropical peatlands in Southeast Asia, generating nearly half of global emissions. Results were validated against national data reported by countries to the UN Climate Convention and against the well-established literature. Overall, the validation yielded a good agreement with these sources. FAOSTAT estimates explained about 60 % of the variability in official country-reported data. The predicted emissions were virtually identical – with over 90 % of explained variability – to official data from Indonesia, currently the top emitting country by drained organic soils. Also, calculated emissions factors for oil palm plantations in Indonesia and Malaysia were in the same range and very close to emissions factors derived from detailed field measurements. This validation suggests that the FAO estimates may be a useful and sound reference in support of countries reporting needs. Data are made available through open access via the Zenodo portal (Tubiello and Conchedda, 2020) with the following DOI: https://doi.org/10.5281/zenodo.3942370.
Highlights
Generally speaking, wet soil ecosystems, characterized by high levels of organic matter, which accumulates in large quantities under the anoxic conditions that exist in the presence of water
As this methodology focuses on agricultural land uses, it does not investigate the impacts of wildlife on the organic soils
We compared FAOSTAT estimates of greenhouse gas (GHG) emissions from the drainage of organic soils in Indonesia to those reported by the country for the period 2000–2016 in the second Biennial Update Report (BUR) to the Climate Convention
Summary
Generally speaking, wet soil ecosystems, characterized by high levels of organic matter, which accumulates in large quantities under the anoxic conditions that exist in the presence of water. Drainage of organic soils releases large quantities of carbon dioxide (CO2) and nitrous dioxide (N2O) into the atmosphere, as a result of the increased oxidation and decomposition rates of the underlying organic matter once water is removed. Restoration of degraded organic soils is currently a priority in several countries as part of their greenhouse gas mitigation and ecosystem restoration commitments under the UN Climate Convention (Leifeld and Menichetti, 2018; Tiemeyer et al, 2020) Measuring current trends, both globally and with country-level detail, is there-. This paper describes additional methodological developments made possible by the availability of timedependent land cover maps, resulting in the production, for the first time, of estimates over a complete time series (1990– 2019)
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