A city’s skyline — the distinctive shapes and arrangements of its buildings — impacts the protection of its population during floods. When the streets flood, pedestrians may be swept under the present and injured or killed. With climate change and rising urbanization, the likelihood and severity of urban flooding are increasing.
Not all city blocks are created equal. In Physics of Fluids, an AIP Publishing journal, researchers from Beijing Normal University, Beijing Hydrological Center, and the China Institute of Water Resources and Hydropower Research investigated how city design contributes to pedestrian safety during flooding.
“Climate change results in an increasing trend of maximum precipitation events when it comes to frequency and intensity,” said writer Zhong-Fan Zhu. “Rapid urbanization alters the hydrological properties of the underlying surface in urban areas. For instance, previous forestland, wetland, and agricultural land have been paved to construct impervious, urban lands. These aspects contribute to frequency occurrences of urban flood events.”
The researchers experimentally identified the flood conditions that make pedestrians vulnerable and utilized computer simulations of various city block patterns, constructing heights, and street widths to evaluate the configurations that best protect people.
Each city has unique buildings and constructing configurations. The team simulated three different urban block layouts: buildings neatly arranged and equally spaced in columns and rows, buildings offset and staggered, and a square tightly outlined by buildings with just 4 buildings enclosed inside.
When buildings are arranged in a line, as within the grid and enclosed layout, they supply a zone of safety by blocking a number of the water and wind. The staggered approach has none of this protection and more danger zones because of increased water and wind circulation.
Altering the constructing shape can even protect pedestrians. Rounding or adding recesses to constructing corners significantly reduced areas of dangerously high floodwater and windspeed. Nevertheless, this intervention also somewhat decreased the protection zone.
Wind was a critical, yet complex, think about determining safety.
“In some cases, the floodwater doesn’t cause pedestrian instability, but adding the wind force will result in a dangerous situation,” said Zhu. “Nevertheless, in other cases, the wind will help to take care of pedestrian stability and protect against floodwater. It looks like that wind is sort of a ‘double-edged sword.'”
Different constructing height arrangements may also help mitigate the negative impacts of wind.
Cities seeking to expand should consider enclosed block arrangements, buildings with rounded and even circular footprints, and potentially seek the advice of with a physicist.
