Climate experts are urging the UK Government to consider the impact of urban sprawl on the weather.

Cities are potentially as big an influence on local rainfall and temperatures as more general, large-scale changes in the climate, they say.

Skyscrapers and closely packed houses are of particular concern, a panel of UK climatologists told the British Association's science festival in Leicester.

Both designs of building could increase local rainfall by creating low-level turbulence in the air, said Professor Chris Collier of the University of Salford in Greater Manchester.

Another issue is so-called "heat islands" created by hot air from factories, cars, and people crammed into cities.

The centre of Manchester, for example, is warmer than surrounding rural areas by about 8 degrees Celsius.

This could change the way the air circulates, leading to an increase in rainfall in certain areas of the city, said Professor Collier.

New approach

Such factors must be taken into account by ministers when they plan increases in housing density, say in the South East of England, he said.

"The way in which the buildings are designed and built will have an impact on local weather," he told BBC News Online. "People need to understand that when you change the building fabric and building density, there will be an impact on local weather.

"We need to investigate it more," he added. "Because those changes could approach the size of the changes that you can get from climate change."

The "heat island" effect in major cities has been recognised for some years and has become a major subject for research. Only last month, scientists in Tokyo warned of the difficulties Japan's first city would face from local increases in temperature.