Development of a coupled biogenic emission module in an earth system model

Abstract:

We couple a biogenic emission module (Model of Emissions of Gases and Aerosols from Nature, MEGAN) to a dynamic land-vegetation model (LM3), a component of the GFDL chemistry-climate model (AM3-LM3), to examine the possible impacts of land use and land cover change on biogenic VOC emissions and therefore atmospheric composition. The biogenic emissions are calculated in each subgrid vegetation and land use tile in LM3, based on parameters including vegetation type, leaf area index, canopy air temperature, and soil moisture. The LM3-MEGAN model computes global isoprene emissions of ~520 Tg C/yr in the year of 2005, comparable to previous estimates. We find that isoprene emissions in this coupled system depend strongly on the diurnal range of canopy air temperature simulated by LM3, leading to significantly higher isoprene emissions than obtained by running MEGAN with atmospheric temperatures from AM3 (~ 380 Tg C/yr). We also find that isoprene emissions simulated by LM3-MEGAN over the eastern United States vary significantly from year to year, although global emission totals remain stable over the same period. Preliminary analysis indicates that this large interannual variability results mainly from strong variations in soil moisture over the US as a result of precipitation changes. LM3-MEGAN will be further evaluated against satellite HCHO columns as well as isoprene fluxes measured at surface sites. We will then apply the LM3-MEGAN-AM3 modeling system to investigate the impacts of land-use change on air quality and radiative forcing in past, present and projected future atmospheres.