Understanding the summertime warming in canyon and non-canyon surfaces

Abstract

Urban landscapes, made of unique buildings, pavements, and vegetation, create complex influences on the atmosphere. These influences induce increased nighttime warming and daytime cooling, especially in arid regions. This study compared three types of surfaces, including rooftop, turfgrass, and canyons, in terms of surface temperature and surface energy fluxes. A 68 sq.km parcel in Phoenix, AZ was considered for comparison. The study found that the canyons' land surface temperatures (LST) were 5 °C lower than the rooftop surfaces. The turfgrass surfaces were 4 °C cooler than the canyon surfaces. Moreover, north and south (N-S) oriented canyons were 2 °C cooler than east and west (E-W) oriented canyons. No significant changes were observed in net radiation for rooftop, turfgrass, or canyon surfaces. However, conductive fluxes, warranting nighttime warming, showed higher absorption of 45 W/m2 on the rooftop surfaces, than in the canyons. The turfgrass showed nighttime cooling, as the heat absorption was 210 W/m2 lower than the rooftop surfaces and 165 W/m2 lower than the canyons. Additionally, a 50 W/m2 difference of heat absorption was observed between N-S oriented canyons and E-W oriented canyons. The study concludes that canyons are major causes of daytime cooling and nighttime warming.