The value of monthly ground reflectance is considered as 0.2 in the
standard simulations. This value is resulted from the combination of
ground reflectivity of pervious and impervious surfaces and based on
equation (1):
\begin{equation}
\rho_{\text{GR}}=\rho_{GR\_p}f_{GR\_P}+\rho_{GR_{\text{imp}}}(1-f_{GR\_P})\nonumber \\
\end{equation}
where PGR is ground reflectance, PGR_P and PGRimp refer to road pervious and impervious fGr_P is road area function. Moreover, the ground reflectance value is affected by ground surfaces cover by snow situation \cite{Clarke_2002}. Since this
study is only focused on the cooling season (for shading design
purposes), the effect of snow is ignored in the presented calculations.
The range of uncertainty in ground reflectance is extracted from Sun et
al. \cite{Sun_2013}. According to this study, the range of ground reflectance
could vary between 0.05 and 0.45 with a center point of 0.25. This value
can be represented through a triangular probability distribution displayed
in Fig.4 .