Reconstruction of Inundation and Greenhouse Gas Emissions from Siberian Wetlands over the Last Half-Century

Changes in greenhouse gas emissions such as methane (CH4) and carbon dioxide (CO2) from high-latitude wetlands in a warming climate may have important implications for projections of global warming, due to the large amounts of carbon stored in highlatitude soils and the high greenhouse warming potential of methane. As much as 1/3 of global natural methane emissions come from high latitudes. Efforts to monitor high-latitude greenhouse gas emissions are hampered by the sparseness of in situ data at high latitudes, especially in Northern Eurasia. While biogeochemical modeling can provide estimates of greenhouse gas emissions in such areas, the lack of in situ measurements also makes it difficult to constrain these models. Fortunately, emissions of greenhouse gases, especially methane, are sensitive to hydrologic variables such as inundation that now can be observed via passive microwave and synthetic aperture radar remote sensors. Here we apply a combination of large-scale hydrologic/biogeochemical models and remote sensing observations across the West Siberian lowlands to estimate soil moisture, inundation, and greenhouse gas fluxes. Our modeling framework consists of the Variable Infiltration Capacity macroscale hydrological model (VIC), extended to include carbon cycling and coupled to a methane emissions model. In particular, our modeling framework includes a parameterization of the spatial distribution of soil moisture, which allows us to compare our simulated emissions to both large-scale remote sensing observations and point-scale in-situ observations. We have calibrated this framework using observed streamflow, inundation products derived from PALSAR and AMSR-E, and in situ water table and greenhouse gas emissions observations. Using the calibrated model, we examine the interannual variability of simulated inundation and greenhouse gas emissions across W. Siberia for the period 1948-2007. Figure 1: VIC overview and the VIC lake and wetland algorithm schematic. Land Surface Hydrology Model • Variable Infiltration Capacity (VIC) Model (Liang et al. 1994) • Water and energy balance closure • Macroscale: grid cells range from 10 to 100 km • Statistical parameterizations of sub-grid variability in soil moisture, land cover • Lake/wetland model (Bowling, 2002) handles changes in lake extent • Grid cell average water table computed as sum of total column soil moisture deficit • Extended to handle carbon cycling with Farquhar photosynthesis, plant respiration, and NPP from BETHY (Knorr, 2000) Sub-grid Variability of Water Table and Inundation • Uses topographic wetness index formulation from TOPMODEL (Beven and Kirkby, 1979) • Relates local water table position to local topography and the average water table depth of the region Methane Model • Walter and Heimann (2000) with modifications described in Walter et al (2001a ) • soil methane production, and transport of methane by diffusion, ebullition, and through plants modeled explicitly • methane production occurs in the anoxic soil from the bottom of the soil column to the water table • methane production rate controlled by soil temperature and NPP (both from VIC) • methane oxidation also taken into account Reconstruction of Inundation and Greenhouse Gas Emissions from Siberian Wetlands over the Last Half-Century Theodore J. Bohn1, Erika Podest2, Ronny Schroeder2, Kyle C. McDonald2, Chun-mei Chiu3, Laura C. Bowling3, Mikhail Glagolev4, and Dennis P. Lettenmaier1 1University of Washington, Seattle, Washington, USA; 3JPL-NASA, Pasadena, California, USA; 3Purdue University, West Lafayette, Indiana, USA; 4Moscow State University, Moscow, Russia AGU Fall Meeting, San Francisco, CA, December 17, 2009 1. Modeling Approach High Biomass/Non-wetland Agriculture Low Biomass/Non-wetland Wetland Open Water 81 82 83 84