(a) Scale effects: Effects of reflective material can change with the scale of its deployment. An illustration of the scale effect is shown in Fig. 1. Intuitively, reflective materials applied on a single building will not exhibit same hydrothermal behavior as those on the entire city, and vice versa. Consider the limiting case: does perfect knowledge of the thermal characteristics of reflective materials on a single building ( Fig. 1c) necessarily allow us to quantify the effect of changing albedo of all roofs in a city ( Fig. 1a), by simply “summing up” numerical modeling results representing street canyons ( Fig. 1b)? For example, a study by Botham et al.  found that placement of a single white roof could enhance local vertical mixing, increased surface temperature on building walls by bringing warm air from other roofs to the street level. When white roofs were deployed on all buildings, this RGD Peptides phenomenon disappeared that temperatures on all urban facets were decreased. In terms of hydroclimate, large-scale deployment of reflective roofs reduces vertical mixing significantly, leading to reduction in regional precipitation and cloud formation  and . When reflective roofs are applied over a single building, this impact will not happen as the reduction of mixing is not strong enough to affect overall turbulent fluxes arising from the city. This apparent size effect necessitates the use of different experimental and numerical tools for characterizing and simulating reflective materials at different scales. Moreover, among the existing large-scale studies (i.e., city, continental, and global scale), it is usually assumed that reflective materials are installed over the entire urban areas, neglecting the spatial distribution inside the city. More practical scenarios need to be considered for future numerical modeling to overcome errors associated with this simplification.