City residents with mental or behavioural disorders – especially those with dementia – are most at risk of dying when temperatures reach 24.5 degrees Celsius or above, a study by local universities has shown.After studying more than 133,000 deaths recorded in the summer months between 2007 and 2014, researchers with University of Hong Kong (HKU) and Polytechnic University (PolyU) found that Hongkongers with mental problems have a lower ability to adapt and prepare in environmental extremes,…