Drainage of organic soils and GHG emissions: validation with country data

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.