Future Precipitation Changes And Their Implications For Tropical Peatlands - GRL

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<1> Carbon (C) in tropical peatlands over Southeast Asia and Amazonia, if released to the atmosphere, can substantially increase the growth rate of atmospheric carbon dioxide. Over Southeast Asia, where the most extensive tropical peatlands in the world occur, 11 climate models for the IPCC Fourth Assessment show an overall decrease of rainfall in future dry seasons. Over Amazonia, future rainfall changes in dry seasons are highly uncertain; five models predict increased rainfall, and the remaining models predict the opposite. We have further examined the UKMO-HadCM3, GISS-ER, and GFDL-CM2.1 models. Over Southeast Asia, all three models predict similar decreases of rainfall and evaporative fraction, implying an increase of water table depth and surface dryness during the dry season south of the equator. Such changes would potentially switch peat ecosystems from acting as C sinks to C sources. Over Amazonia, the two models with the best simulations of current rainfall produce conflicting results for the future of peat stability.

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<3> As the earth's climate changes in the 21st century, we do not know whether tropical peatlands will continue accumulating C or will shift and begin releasing C to the atmosphere because of anticipated changes in rainfall and surface dryness. If more frequent drought events were to occur in the future associated with less rainfall and higher temperatures, the groundwater level would decrease, leading to a more flammable environment and accelerated oxidative loss of peat . On the contrary, if future climates over tropical peatlands were more humid, then peatlands might continue removing C from the atmosphere. Therefore knowing how rainfall will change in tropical peatlands should clarify the future nature and magnitude of this carbon-climate feedback.

<4> Apparently, no studies have addressed how changes in future rainfall would impact tropical peatlands. Using the 11 coupled ocean-atmospheric models of the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), we analyze current and future climate over the two largest regions of threatened tropical peatland, i.e., Southeast Asia and Amazonia. Southeast Asia has the most extensive tropical peatlands in the world with an estimated area between 20 and 30 M ha largely distributed in Indonesia (Sumatra, Kalimantan, and Papua) and Malaysia (Peninsula Malaysia, Sarawak, and Sabah) . Small peatland areas remain in the Philippines, Thailand, Vietnam, and Brunei. The peatland area over Amazonia is estimated to be about 2.8 M ha largely occurring in the middle Amazon and marshy plains near the Bolivian border, and to a lesser extent in Venezuela and Colombia . Depths in excess of 10 m are characteristic of peatlands in Southeast Asia and less in Amazonia.

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<18> We have analyzed changes in the dry season rainfall over Southeast Asia and Amazonia peatlands as part of the global climate change predicted by 11 models participating in the IPCC AR4 under the SRES A1B scenario. Over Indonesian peatlands, where the most extensive peatlands in the world occur, 7 models predict a decrease of future rainfall during the dry season. In addition, 9 of the 11 models suggest a greater interannual variation of future dry season rainfall. The more consistent decrease of rainfall during the dry season is found in South Sumatra and southern Borneo where most peatland in Indonesia is located. Water table depth and net solar flux are predicted to increase and EF is predicted to decrease over southern Indonesia accompanying rainfall decreases.

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