Sydney, Feb 19 (IANS): Some of our cities could be as much as four degrees warmer than the surrounding countryside, warn scientists.

The preponderance of concrete structures and bitumen in our cities absorb and store heat, making them warmer than the surrounding areas, especially at night.

And on rainy days these hard, non-porous surfaces also prevent water being absorbed into the ground so that little moisture remains in the urban environment.

Scientists are now using thermal imaging to work out how plants can be used to reduce severe temperatures in our cities.

A team from the Universities of Melbourne and Monash is trying to establish how street trees, parks, green roofs and green facades (collectively known as green infrastructure) can interact with urban design to reduce temperatures in cities.

Their results show that leafy, green streets and irrigated open space areas were much cooler than built up urban areas without green infrastructure, according to a Monash and Melbourne statement.

Melbourne researcher Nick Williams said: "Plants are attractive, natural air conditioners so we should be using them more to cool cities.

"As well as providing shade, plants also cool cities by evaporating water through their leaves into the atmosphere."

"Irrigating green infrastructure with the abundant storm water found in our cities will increase its cooling ability and use water that would otherwise go down the drain," added Williams.