Urban ecosystems play a central role in global and regional climates by disrupting the surface energy balance and modifying nutrient and water cycling. Cities recognize the need for urban design strategies that address urbanization-induced climate stress but are limited by a lack of ecological knowledge to guide best practices in urban planning and design for climate adaptation. This dissertation combines remote sensing, field data collection, stable isotope analysis, and ecosystem modeling techniques to advance our understanding of core processes related to vegetation, heat, and water within urban climate systems.
Combining and adapting models of photosynthesis, stomatal conductance, and evapotranspiration, we produce and validate fine spatiotemporal resolution estimates of latent heat flux from urban vegetation that account for unique urban climatological and physiological processes. The innovative modeling framework captures spatial heterogeneity in cooling benefits across the complex landscape of cities at a scale useful for informing policies aimed at mitigating urban heat exposure.
We assess the effectiveness of urban greening and albedo manipulation to reduce surface temperatures across climate types in a spatial regression modeling framework. We find significant variability in the surface cooling efficiency of different vegetation forms, with tree cover cooling impacts approximately four times as strong as grass cover cooling impacts. Our results identify surface moisture as a powerful control on vegetation cooling efficiency, highlighting the role of background climate in selecting climate adaptation strategies.
Using observed relationships between tree cover, albedo, and surface temperature, we demonstrate the importance of urban land cover composition in guiding effective climate adaptation strategies. Residential regions that are most vulnerable to extreme heat in Boston, Massachusetts are characterized by low canopy cover, few opportunities for tree planting, and a large proportion of flat, dark roofs, making white roof programs a promising strategy for reducing heat exposure disparities.
In a field study of unirrigated street trees, we identify precipitation as the primary water source for trees confined to tree pits in a mesic city, supporting the storm water mitigation function of urban vegetation. However, the high proportion of water utilized from precipitation demonstrates the potential vulnerability of street trees to drought stress and points to water supplementation during dry periods as a possible key improvement in urban greening initiative implementation. Altogether, the results presented in this dissertation provide novel information to guide improved urban sustainability, resilience, and equity in a changing climate.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49148 |
| Date | 13 August 2024 |
| Creators | Smith, Ian Andrew |
| Contributors | Hutyra, Lucy R. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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