Triangular cities appear to experience the least amount of rain compared to square or circular ones, a new study has found. The authors behind it believe the way wind and weather interact with shape in city environments could be a consideration when designing the urban spaces of the future which will need to be more tolerant to the effects of the climate crisis.

Floods in cities are an increasing concern as changes to the climate exacerbated by human activity mean we are experiencing an increasing number of extreme weather events. Cities are particularly vulnerable to things like flash floods as the vast expanses of concrete jungle (where dreams are made of) have poor drainage.

A new research article published in Earth’s Journal explored whether the shape of a city could influence the weather, representing the first investigation of its kind into the way urban rainfall differs from that seen at inland and coastal environments. The authors were inspired to look into the influence of shape after noticing that some of Earth’s seemingly wetter cities, like London, were also circular.

Looking at circular, square, and triangular cities (like Dallas, New York, and Los Angeles, respectively) they compared the results of Weather Research and Forecasting models and eddy simulations of air currents to see how shape could influence the weather. They also compared this to outer-city areas both inland and along coastlines.

The results revealed that the influence of shape is greater in cities in coastal settings as airflow from the city interacts with sea breeze. Circular cities had the most rainfall being 78.6 percent higher than that seen in triangular ones.

Overall, rainfall volume and intensity revealed a rain-attracting-shapes ranking of circular > square > triangular, with triangular cities receiving the least and calmest variety of rain overall.

“With the consideration that climate change will intensify rainfall hazards in the future, global cities have spent vast resources to study and implement a variety of infrastructures as adaptation strategies,” write the study authors. “Our results identify a hitherto poorly understood but an important role of urban layout especially in the coastal regions. Circular city shape shows potential risks of extreme rainfall and resultant flood risk.”

The authors however note that the findings aren’t without their limitations and hope to tackle some of these by next investigating the impact of city shape under a variety of wind conditions. For now, they conclude the study constitutes food for thought in the way we can address some issues of sustainability when developing our urban spaces.

“This study provides the first investigation of the impact of city shape on urban rainfall in inland and coastal environments... The finding is valuable for sustainable and resilient city planning especially for those undergoing expansion.”