This is the first thermal satellite image of Hong Kong taken in summer - and it shows just how hot the nights can get in urban areas. The high-resolution image, taken by Nasa's Terra satellite at 10.40pm on August 4, shows broad swathes of Kowloon sweltering in temperatures of 32 degrees Celsius or higher (shown as white and red on the map). It was taken for researchers at Polytechnic University who are studying the urban heat island effect in Hong Kong - the tendency for densely populated urban areas to become much warmer than nearby rural areas. Janet Nichol, associate professor in its department of land surveying and geo-informatics, said the picture - taken during a record-breaking 12-day period of very hot weather - was the shape of things to come. 'The temperatures are exceptionally hot for the night ... It is a very, very good example of the extreme of the urban heat island effect we might expect in future. Based on predictions of a three degree increase in air temperature in Hong Kong by 2050, these periods may become quite commonplace in the next 10 years.' Professor Nichol, who runs the project with Dr Lam Ka-se, of the department of civil and structural engineering, said the image was taken using a novel technique that is accurate to within 10 metres - nine times the resolution of a typical satellite image. The variation is caused by the greater heat absorbency of man-made materials and concentrations of tall buildings which limit air flow. Professor Nichol said the urban heat island had expanded markedly into Hung Hom and Whampoa and towards West Kowloon since the team's first satellite picture of Hong Kong was taken in January. The 490-metre-high International Commercial Centre and subway station under construction at Union Square could be factors, while air conditioners were a likely contributor in mixed residential and commercial areas. 'We didn't expect to see any heat island effect in the Union Square area because it is near the coast,' she said. 'This could be the start of a general expansion of the heat island towards southwest Kowloon.' Residents of Tai Kok Tsui are campaigning against plans to build a 40-storey tower block they say will complete a 'great wall' of buildings that will block the area's last air corridor.