Impacts of urban albedo increase on local air temperature at daily through annual time scales: Model results and synthesis of previous work

We use urban and soil-vegetation surface parameterization schemes combined with one-dimensional (1-D) boundary-layer mixing and radiation parameterizations to estimate the maximum impact of increased surface albedo on air temperatures within and immediately above the urban canopy. Impacts of extensive albedo increases in two Chicago IL neighborhoods are modeled. Clear-sky summertime reductions of diurnal maximum air temperature for residential and downtown core neighborhoods are significant; however, realistic impacts will be smaller because the 1-D modeling approach ignores advection. The analysis is extended to seasonal and annual time scales in the residential neighborhood. Annual cooling degree day decreases are approximately offset by heating degree day increases and the frequency of very hot days is reduced. Despite the variability of modeling approaches and scenarios in the literature, a consistent range of air temperature sensitivity to albedo is emerging; a 0.10 average increase in neighborhood albedo (a 0.40 roof albedo increase for a roof area fraction of 0.25) generates a diurnal maximum air temperature reduction of approximately 0.5 °C for “ideal” conditions, i.e., a typical clear-sky mid-latitude summer day.