Pedestrian Wind Comfort: How much topology should I include if I am studying a site in hilly or mountainous terrain?

As an educated estimate, 3-5 times the reference height of the site of interest should define the amount of terrain that should be included. For example, if there is a 1000 meters high mountain then try to include at least 3000-5000 m of terrain.
Kindly be aware, that this could be a computationally expensive approach