Characteristics of tropical nights in the Warsaw area from 1951 to 2024

Abstract An analysis of tropical nights (TNs) – namely, nights during which the air temperature does not fall below 20°C – showed a significant increase in number in the Warsaw metropolitan area during the multiannual period 1951–2024, especially since the late 1980s. Over the course of a year, TNs occurred from May to August, most often in July (47% of cases), but they are becoming increasingly common from as early as June. TNs have been observed to occur increasingly frequently in sequences of several days – of up to five in a row. There were 20 cases when TNs occurred at all four stations studied at the same time, and as many as 16 of these were noted in 2010–2024. The greatest number of TNs were recorded at stations in the centre of Warsaw, close to built-up areas, and the lowest at stations far from the centre, confirming that the urban heat island has a significant influence on the occurrence of TNs.