Urban Biosphere

Figure 1. Spatial patterns in aboveground biomass (AGB) and carbon fluxes in the Boston area. Arrows correspond to mean annual C fluxes for 2013 (gross ecosystem exchange-green, ecosystem respiration-red, Anthropogenic emission-black) with arrow direction indicating C movement into (down) or out of (up) the ecosystem. Fraction of impervious surface area (ISA), atmospheric CO2 mixing ratio, and mean AGB are listed for reference. Pie charts show relative anthropogenic emissions source sectors (Hardiman et al 2017)

Urban areas are a heterogeneous mix of fossil and biological CO2 and CH4 emissions and biological CO2 sinks.  The magnitudes of these fluxes vary diurnally and seasonally depending on phenology, climate, land use practices, urban form, and the local energy portfolio.  Despite the dominance of fossil emissions and impervious surfaces within cities, biological activity significantly influences urban CO2 and CH4 mixing ratios, and if not properly accounted for, can bias results from atmospheric inversions (Figure 1).  However, the vegetation influences on CO2 and microbial influence on CH4 are not universal due to different bioclimatic limitations and variations in vegetation density, location of landfills, etc. Much of the literature currently treats biological carbon fluxes from urban vegetation as negligible, introducing biases of unknown magnitude into the measurement and modeling of the urban carbon cycle.

For this synthesis effort, we will produce biosphere CO2 flux estimates for target year(s) (2015~2016) for each of the study cities (Boston, DC/Baltimore, Indianapolis, Los Angeles, Salt Lake City, and San Francisco), including updating the parameterization for the different regional vegetation types. A preliminary version of this model has been created and run for the NE USA (Figure 1, building from Hardiman et al. 2017).  These model results will be used as inputs for inverse modeling analysis across cities to test sensitivity and assess the role of biological fluxes across seasons, intensities of urban development, and bioclimatic regions.

Key contact: Lucy Hutyra (lrhutyra at bu.edu)