Taking advantage of meteorological data which come from automatic stations, published by WIOŚ, it was tried to assess the intensity of urban heat island in Warsaw. This was based on air temperature values measured at the height of 2 m above the ground which were gathered in a period from IX 2003 to VIII 2006 in four urban background stations in Warsaw, one of them in Piastów and one regional background station in Legionowo. The last one was situated behind the influence of Warsaw agglomeration. On the base temperature values the differences between each of Warsaw and Legionowo stations were stated what allowed to define the intensity and the time of occurrence of the urban heat island. The schedule of frequency of those differences was made and the special graphs shows development and disappearance of the heat island in various parts of the day depending on different seasons.

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