Caitlin Semmens

The aim of my research is to investigate how the spatial heterogeneity or "patchiness" of urban surfaces affects turbulent exchange in cities. Much of our understanding of land-atmosphere interactions is rooted in direct flux measurements by the eddy covariance (EC) method. This stationary, tower-based approach has become the standard tool for monitoring the terrestrial carbon cycle, trace gas emissions, and the water balance. However, despite its use in many cities globally, the EC method was initially developed for ecosystems like croplands and forests, where the source area has a uniform or homogeneous distribution of sources and sinks. This is not the case in urban ecosystems, where emission sources of heat, water, and trace gases vary both spatially and temporally. To date, few studies have addressed source heterogeneity on the ability to measure fluxes in urban settings. And there have been no studies that analyze long-term urban flux data seasonally, and relate it to remotely-sense geospatial information. Properly describing the unique surface-atmosphere exchanges of heat, momentum, water vapour, and trace gases in cities is critical for urban-scale weather and air pollution forecasting.