By advecting thermal energy into soil, precipitation regulates the near-term global warming potential of thawing permafrost.
In Interior Alaska, at a thawing wetland complex located within a black-spruce permafrost forest, we measured carbon, water, and energy exchange between the land and the atmosphere over three years (2014, 2015, 2016). The dataset is unique because the study captured an average precipitation year and two years with abnormally high rainfall. Researchers from the University of Washington found that interactions between rain and deep soil temperatures controlled methane emissions. When wetland soils were warmed by spring rainfall, methane emissions increased by ~30%.
Northern regions are expected to receive more rainfall in the future. By warming soils and increasing methane release, this rainfall could increase near-term global warming associated with permafrost thaw.
Because the world is getting warmer, permanently frozen ground around the Arctic, known as permafrost, is thawing. When permafrost thaws, the ground collapses and sinks. Often a wetland forms within the collapsed area. Conversion of permanently frozen landscapes to wetlands changes the exchange of greenhouse gases between the land and atmosphere, which impacts global temperatures. Wetlands release methane into the atmosphere. Methane is a potent greenhouse gas. The ability of methane to warm the Earth is 32-times stronger than that of carbon dioxide over a period of 100 years. In this study, researchers found that methane released from the thawing wetland was greater in rainy years when rain fell in the spring. The data indicated that when it rained, water from the surrounding permafrost forest flowed downhill, entered the wetland, and rapidly altered wetland soil temperatures down to deep depths (~80 cm). Rain has roughly the same temperature as the air, and during springtime in northern regions, the air is warmer than the ground. The microbial and plant processes that generate methane increase with temperature. Therefore, wetland soils, warmed by spring rainfall, supported more methane production and release. This study identifies an important and unconsidered role of rain in governing the radiative forcing of thawing permafrost landscapes.
BER Program Manager
Daniel Stover SC-23.1
Terrestrial Ecosystem Science
Office of Biological and Environmental Research
Rebecca B. Neumann
Associate Professor, Civil & Environmental Engineering
University of Washington, Seattle, WA
This material is based on work supported, in part, by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under Award Number DE-SC0010338 to R.B. Neumann and the U.S. Geological Survey Land Change Science Program. Considerable logistic support was provided by the Bonanza Creek LTER Program, which is jointly funded by the National Science Foundation (NSF; DEB 1026415) and the U.S. Department of Agriculture Forest Service, Pacific Northwest Research Station (PNW01-JV112619320-16).
Neumann, R. B. et al. “Warming effects of spring rainfall increase methane emissions from thawing permafrost.” Geophysical Research Letters 46(3), 1393–1401 (2019). [DOI:10.1029/2018GL081274]
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