of the city during the afternoon rush hour on July 8, 2013 flooding city streets, subway tunnels, basements and knocking out power for over two million residents, stranding commuters, some having to be rescued from a submerged train. A daily rainfall record of was set at Pearson Airport, most falling in an hour and a half. Flood insurance claims are likely to exceed the 2005 storm due to a wider area affected. In the springs of 2017 and 2019, heavy rain combined with snowmelt led to the water levels of Lake Ontario to rise to record levels, flooding parts of the Toronto Islands and closing it to the public. The most severe heat wave in Toronto occurred in 1936, during the 1936 North American heat wave, when downtown temperatures in Toronto exceeded on three consecutive days (July 8 – 10), with nighttime temperatures not falling below . The city was ill-equipped at that time to handle such a prolonged extreme heat wave, and heat stroke claimed 225 lives in the city, not counting indirect deaths from causes such as drowning. The hottest month recorded, however, was July 1921, when the average maximum temperature downtown was , with a monthly mean temperature of , this was equalled in July 2020. At Toronto Pearson International Airport, the highest monthly maximum average was in July 1955, however the highest mean of was set in July 2020, records there began in 1937. The highest humidex (combined feel of temperature and humidity) reached at the airport during the heat wave of July 1995, downtown it reached on July 21, 2011 during the 2011 North American heat wave. The coldest minimum temperature of was recorded on January 10, 1859. The coldest temperature recorded at the airport was on January 4, 1981, and the coldest windchill recorded was on the same day. The coldest month overall was at the airport in February 2015 and at downtown in February 1875. Other notable cold waves occurred in January 1994 and February 1934. Winter cold snaps pose a danger as they often come with high winds, leaving the city's homeless population very prone to frostbite and hypothermia. Upward temperature trend Based on public records provided by Environment Canada, the average annual temperature has increased at Pearson Airport over a period of 30 years. If compared with the thirty-year normals from 1971 to 2000, more of this increase occurred at night: