Microclimate Patterns of Residential Landscapes Across the US

Abstract:

Urban development has altered the physical and biological properties of native ecosystems worldwide. Research on the environmental outcomes of development continues to increase in scope. Climate phenomena, such as the Urban Heat Island (UHI) and Park Cool Island (PCI), are frequently used to illustrate how cities and managed landscapes differ from rural lands. The UHI describes the disparity between urban and rural temperatures, and results from heat retention within the built environment. These effects may be locally mitigated by vegetation (PCI). While the UHI is a useful tool for examining cities on a large scale, the methods are often too coarse to describe what individuals experience. We wondered: What large-scale climate trends are detectable at microclimate levels? Are microclimate patterns within residential landscapes typical, or are they geographically variable? To investigate, we installed sensors to monitor the air temperature within yards (residential landscapes) and native landscapes of 6 US cities from unique climate zones; Los Angeles, Phoenix, Minneapolis, Baltimore, Miami, and Boston. We hypothesized that microclimate trends would be similar among cities, and that microclimate patterns would predominate over large-scale climate trends within residential landscapes, especially when atmospheric mixing is low.

Air temperature data collected between Aug. 2012 and July 2014 reveal that residential landscapes experience significantly different temperatures than native landscapes (pre-sunrise). The differences drive cities toward similarity, despite the variability of climate zones. The 6 cities also experience similar patterns of diurnal temperature fluctuations. Daily temperature ranges in yards are significantly greater than in their corresponding native landscapes during cooler months (p < 0.05; Oct – Mar, except Boston; no difference), and greater (p < 0.05; Baltimore and Miami) or not significantly different from May - September. Our results suggest that microclimates in residential landscapes can create local heat sinks within the built environment that may alleviate UHI effects in some cities. Additionally, microclimates found in yards follow similar trends among cities, which can contribute to homogenization of urban environments across the US.