is slightly milder than locations further inland. Winters are cool with frequent cold days, while the summers are mild to warm, with occasional hot temperatures. Temperature rises above 30 °C on average 4 days each summer, while (night) temperatures can drop below -5 °C during winter for short periods of time, mostly during periods of sustained easterly (continental) winds. The following climate data is from the airport, which is slightly cooler than the city, being surrounded by water canals which make the climate milder and with a higher relative humidity. The city has an urban heat island, especially inside the city centre. Demographics Rotterdam is diverse, with the demographics differing by neighbourhood. The city centre has a disproportionately high number of single people when compared to other cities, with 70% of the population between the ages of 20 and 40 identifying as single. Those with higher education and higher income live disproportionately in the city centre, as do foreign-born citizens. 54% of city centre residents are foreign-born, compared to 45% in other parts of the city, while in the city centre 70% of businesses are run by foreign-born people. Nonetheless, this is not a comment on income, as 80% of homes are rented in the city centre. Composition The municipality of Rotterdam is part of the Rotterdam-The Hague Metropolitan Area which, as of 2015, covers an area of 1,130 km2, of which 990 km km2 is land, and has a population of approximately 2,563,197. As of 2019, the municipality itself occupies an area of 325.79 km2, 208.80 km2 of which is land, and is home to 638,751 inhabitants. Its population peaked at 731,564 in 1965, but the dual processes of suburbanization and counterurbanization saw this number steadily decline over the next 2 decades, reaching 560,000 by 1985. Although Rotterdam has experienced population growth since then, it has done so at a slower pace than comparable cities in the Netherlands, like Amsterdam, The Hague and Utrecht. Rotterdam consists of 14 submunicipalities: Centrum, Charlois (including Heijplaat), Delfshaven, Feijenoord, Hillegersberg-Schiebroek, Hook of Holland, Hoogvliet, IJsselmonde, Kralingen-Crooswijk, Noord, Overschie, Pernis, and Prins Alexander (the most populous submunicipality with around 85,000 inhabitants). One other area, Rozenburg, does have an official submunicipality status since 18 March 2010. Since the status of a submunicipality was lifted on 19 March 2014, it became an integral part of the municipality of Rotterdam . The size of the municipality of