Urban fog

E. Linacre


Measurements in Munich have shown that radiation fog in winter is least in the city centre (about 25 days each year), and most frequent (around 60d/a) in the rural outskirts 10 km away (1). Observations show that the difference is largely due to a temperature difference (urban heat island effect), not to dewpoint difference. The incidence of fog in the city centre erratically declined a little during 1961-1990, but increased slightly in the outskirts. However, there was a considerable reduction in the suburbs, at 5 km from the city centre, from about 60d/a to about 20d/a. This is attributed to urbanization of the suburban areas, and a strengthening of the nocturnal breeze from the country to the city centre as urban heating increased.



(1) Sachweh and F. Koepke 1997. Fog dynamics in an urbanised area. Theor. Appl. Climatol., 58, 87-93.