Urbanization alters surface energy and biogenic carbon (C) exchange processes which can exacerbate increases in near-surface temperature and complicate municipal-scale efforts to address the local causes and impacts of climate change. This dissertation integrates field- and remote-sensing datasets to evaluate the magnitude of and spatial patterns in albedo and biogenic C fluxes in the urban landscape, focusing on the region of Greater Boston, Massachusetts.
Using surface reflectance measurements from the Landsat and MODIS satellites, we show mean albedo in the Boston metropolitan region was significantly lower in core population centers than nearby rural areas, corresponding to reduced tree cover, greater impervious surface area, and higher surface temperatures. These results establish albedo decline as a gradient in landscape-scale features of urbanization, and offer context for efforts to mitigate extreme urban temperatures through raising the albedo of built surfaces.
Pairing field measurements of tree growth with LiDAR-based data on tree biomass and canopy cover, we estimate the distribution of annual woody biomass C uptake in the city of Boston. A substantial portion of tree C uptake occurred in densely developed residential areas dominated by open-grown trees as well as remnant forest fragments. Our results show that estimates based on rural tree growth may under-predict C uptake by up to approximately 50%, and quantifies the scope for policy interventions aimed toward increasing ecosystem services output from the urban forest.
Fusing measurements of soil respiration and net vegetation productivity in lawns and trees with high-resolution land surface data, we develop an improved estimate of annual biogenic net carbon fluxes in Boston at a 30 m resolution. We find forested areas of the city may be a modest net sink for C (median 2.7 GgC yr-1), but also estimate substantial C flux from intensively managed landscapes in residential areas. Estimated city-wide biogenic C was relatively small (median 600 MgC yr-1), potentially offsetting less than 1% of estimated annual fossil fuel emissions. Our results imply net biogenic C flux likely will contribute little towards efforts to reduce local net greenhouse gas emissions, but may significantly influence urban atmospheric CO2 concentrations at certain times and places
