Current flood models do not account for cities’ impact on local rainfall patterns, which could end up causing urban planners to significantly underestimate the impact and frequency of floods in urban areas, according to a new Purdue study.
The study showed that impermeable surfaces such as concrete can affect how a rainfall spreads across an area, sending runoff into drains and waterways—along with pollutants—instead of infiltrating it, and failure to incorporate this information into flood models could result in the strength, timing and duration of floods being underestimated by as much as 50%, as well as affect water quality.
Previous research suggested that if 5% or more of a watershed is covered with impervious surfaces, local hydrology begins to change, with exponentially greater affects for larger areas of impervious surface.
Simulations showed that a region's hydrological response depends on two factors: the amount of impervious coverage and the spatial pattern of rainfall—e.g,. whether rain falls across the watershed in a random way or is more centralized over impervious areas.
Read more about this study and its findings.