Where Are White Roofs More Effective in Cooling the Surface?

Abstract

By reflecting more sunlight, white (cool) roofs experience lower surface temperatures and produce less heating of the surrounding air. The effectiveness of cool roofs, quantified by the surface temperature difference between cool and regular roofs (ΔTs), is known to vary spatially. A common perception is that ΔTs is controlled by solar radiation that reaches the roof surface. Here we use an Earth System Model and a surface energy balance model to show that the spatial variability of ΔTs, when normalized by the albedo difference between cool and regular roofs Δα, is also controlled by an energy distribution factor that encodes the efficiencies of surface energy balance components in dissipating heat. Our results suggest that painting the roof white is more effective when the roof has less water-holding capacity and smaller thermal admittance and is located in places with more solar radiation, less precipitation, and lower wind speed.