Urban heat island mitigation strategies and lizard thermal ecology: landscaping can quadruple potential activity time in an arid city

A global warming of 2 °C is predicted to drive almost half the world’s lizard populations to extinction. Urban heat island (UHI) effects may further exacerbate the impacts of climate change on organisms that are sensitive to small changes in temperature. Currently, the Phoenix metropolitan region in Arizona, USA, is an average of 3 °C warmer than the surrounding desert. With continuing urbanization and climate change, thermal stress will become an increasingly important facet of urban ecology in coming decades. The main objective of our study was to investigate which landscaping styles and microhabitat variables can most effectively reduce the surface temperatures experienced by lizards. Using a bare lot as a control, we placed copper lizard models with data loggers in several vegetation and irrigation treatments that represent the dominant backyard landscaping styles in Phoenix (grassy mesic with mist irrigation, drip irrigated xeric, unirrigated native, and a hybrid style known as oasis). Our lizard models recorded 6915 estimates of potential body temperatures. We show that lizard activity time in summer was restricted to a few hours in un-irrigated native desert landscaping, while heavily irrigated grass and shade trees allowed for continual activity during even the hottest days. Shade, humidity, and sky view factor explained the majority of variation in temperature at a sub-meter scale. We suggest that maintaining the existing diversity of landscaping styles (as part of an ongoing UHI mitigation strategy targeted at humans) will be beneficial for lizards.