Weathermen find that life is wetter in the suburbs

Rain, the Bible tells us, falls equally on the just and the unjust. But new research adds that more of it drops on people living near cities.

Rain, the Bible tells us, falls equally on the just and the unjust. But new research adds that more of it drops on people living near cities.

The studies, carried out both in Britain and across Europe, show that cities create rain which is then dumped on suburbs and nearby countryside.

The British rain research - carried out, aptly enough, in Manchester, and published in the journal Atmospheric Research - suggests that both the shape of cities and the way they heat up the air around them swells rain clouds, which are then blown by the wind to drop their contents nearby.

Partly because of this and partly because of the hills around it, the centre of Manchester is relatively dry, insists Dr Alan Gadian, a lecturer in atmospheric physics at the University of Manchester's Institute of Science and Technology and one of the authors of the study. "In the city itself rainfall is relatively low," he says. "It is when you go out about five miles to places like Stockport that you get a lot of it." He has even studied an incident in the 1960s where, he believes, Manchester was partly to blame for a torrential downpour that hit Halifax, some 25 miles away.

Dr Gadian and a former colleague, Dr Jutta Thielen, say that cities heat up the air around them by several degrees, both because of the energy burnt in cars and buildings and because tarmac and concrete absorb and then release this heat. This causes columns of warm air to rise into the atmosphere carrying moisture high enough for clouds to condense and form rain. Tall buildings and other "rough" features in cities can have a similar effect by obstructing the air and creating turbulence.

The scientists have refined their findings using a computer model of rainfall in Paris, but believe it would apply to cities all over the world. The findings could also explain why people living near cities often get drenched by unforeseen downfalls because, the researchers say, weather forecasts work on a much broader scale and miss such local effects.