GLOBAL SYMPOSIUM ON SOIL ORGANIC CARBON, Rome, Italy, 21-23 March 2017 An expert system model for mapping tropical wetlands and peatlands

Our understanding of wetlands’ services is currently constrained by limited knowledge on their distribution, extent, volume, inter-annual flood variability, and disturbance levels. We here present an expert system to report on wetland and peat areas, depths and volumes, which relies on three biophysical indices that capture three fundamental properties of wetlands: 1. Long-term water supply exceeding atmospheric water demand; 2. Annually or seasonally water-logged soils; 3. A geomorphological position where water is supplied and retained. Tropical and subtropical wetlands cover 4.7 million km2. In line with current understanding, the American continent is the major contributor (45%) and Brazil, with its Amazonian inter-fluvial region, contains the largest tropical wetland area (800,720 km2). Our model suggests, however, unprecedented extents and volumes of peat in the tropics, mainly outside Asia: 1.7 million km2 and 7,268 (6,076-7,368) km3, which more than three-fold current estimates. Unlike current understanding, South America (particularly Brazil) contributes the most to tropical peat area and volume (ca. 44% for both) partly related to some yet unaccounted extended deep deposits but mainly to extended but shallow peat in the Amazon Basin. Asia has a second place (38% for both tropical peat area and volume). Indonesia is the main regional contributor and still the holder of the deepest and most extended peat areas in the tropics. Africa hosts much more peat than previously reported but climatic and topographic contexts leave it as the least peat forming continent.