Does it ever feel like the rain always falls where you live? You may have a point. It has long been known that urban environments modify their own weather, and a study has confirmed that cities also modify the weather in the surrounding area, with communities living downwind of a city more likely to bear the brunt of the rain.
Acres of tarmac, skyscrapers and miles of suburbs all alter the amount of solar energy that land absorbs and re-radiates. The built environment modifies the weather that a city receives; but how far does a city’s influence over the weather extend?
Qi Li, from Cornell University in New York, and colleagues monitored summer rainfall patterns over a 60km (37 mile) radius of 27 US cities over a six-year period. Their results, published in Earth’s Future, found that more than 80% of cities they monitored had a significant increase in rainfall in the downwind direction.
Dallas, Charlotte, Washington DC, Baltimore and Columbus showed the strongest effect, while coastal cities and unusually shaped cities bucked the trend.
The study found that the higher the wind speed, the further the city’s influence over rainfall extended, with the heaviest rain falling in a 20-40km radius downwind of a city. And in general, the larger the city, the greater its rainfall enhancement effect.
