Transport of thermal energy by rain in thawing permafrost landscapes - Becca Neumann, University of Washington

Becca Neumann, Associate Professor, Civil & Environmental Engineering, University of Washington

Abstract: Northern high latitudes are expected to get warmer and wetter. There is consensus that warming will intensify permafrost thaw and increase wetland methane emissions, facilitating a positive climate feedback. However, the effects of increased precipitation are uncertain. At two different thawing wetland complexes in Alaska, we found that rain rapidly altered soil temperature, both within the permafrost plateau and within the thaw wetland. To a first approximation, rain has the same temperature as air, and when air and soil temperatures are mismatched, rainwater inputs can rapidly change subsurface soil temperatures through thermal conduction. At one site, we found that when wetland soils were warmed by spring rainfall, methane emissions increased by ~30%. The warm, deep soils early in the growing season likely enhanced both microbial and plant processes that increased emissions. At the other site, data showed rapid thaw of frozen soil within the permafrost plateau during a large rain event. This result indicates, but does not prove, that thermal transport by rain could be an important mechanism for thawing permafrost. The collective datasets clearly demonstrate the ability of rain to advect thermal energy into soils, and indicate that through this mechanism, rain notably affects the radiative forcing of thawing permafrost landscapes.

About the Speaker: Becca joined the Civil and Environmental Engineering Department at University of Washington in 2011 and is currently an associate professor. She leads the hydro-biogeochemistry research group, which investigates how hydrologic, chemical and biological processes interact in soils, aquifers and surface waters to control the movement and concentration of chemicals in air, water, plants and animals. The group harnesses knowledge and techniques from multiple disciplines to tackle societally relevant topics, such as food and water quality and global climate change. Prior to UW, Becca was a NOAA Climate and Global Change postdoctoral fellow at Harvard University and a Ph.D. student at the Massachusetts Institute of Technology. She worked as an environmental engineering consultant for EG&G Technical Services before graduate school, and received her B.S. in Civil and Environmental Engineering and B.A. in Art and Art History from Rice University. Outside of work, Becca enjoys hiking, skiing and rock climbing with her husband and two kids.

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Start date
Tuesday, March 16, 2021, 3 p.m.