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Heat waves in Poland in the period 1951-2015: trends, patterns and driving factors

Wibig J.

Meteorology Hydrology and Water Management. Research and Operational Applications

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2018

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Vol. 6, Iss. 1

37--45

EN

Heat waves were analysed on the basis of maximum daily temperature from 24 meteorological stations in Poland. Heat waves are defined as the longest continuous period during which Tmax (daily maximum air temperature) is equal to or higher than 30°C in at least three days, the mean Tmax during the whole heat wave is equal or higher than 30°C and Tmax does not drop below 25°C during the whole period of heat wave duration. Heat waves occur in Poland from April to September with their maximums in July and August. Four-day-long heat waves are most frequent but the longest one lasted 31 days. The most persistent heat waves were in 1994 and 2015. An increasing trend in heat wave frequency and intensity is observed in Poland, however the increase is statistically significant at only about 60% of analysed stations. Four synoptic patterns favouring heat waves have been distinguished. A strong high over the Azores accompanies all of them, as well as slightly higher than normal pressure over Central Europe – this causes calm and sunny weather over Poland. Strong blocking appears over the North Atlantic during heat wave events, proofing that the development of strong heat waves in Poland is related to large scale circulation and that they are not of local origin. The analysis of the impact of soil moisture in months leading up to the development of heat waves should be the next step in analysis.

2

Changes in thermal extremes in Poland

Graczyk D., Kundzewicz Z. W.

Acta Geophysica

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2014

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Vol. 62, no. 6

1435--1449

EN

Changes in thermal extremes of the climate of Poland in 1951-2010 are examined. Warm extremes have become more frequent, while cold extremes have become less frequent. In the warming climate of Poland, the increase in the number of extremely warm days in a year and the decrease in the number of extremely cold days in a year have been observed. Also the increase of the maximum number of consecutive hot days in a year and the decrease of the maximum number of consecutive very cold and extremely cold days in a year have been observed. However, the trends are not of ubiquitous statistic significance, as the natural variability is strong.

3

Występowanie pogody gorącej w Warszawie (1951-2009)

Kossowska-Cezak U.

Przegląd Geofizyczny

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2010

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Z. 1-2

61-75

PL

W artykule zbadano liczbę dni z temperaturą maksymalną > 20°C, > 30°C i > 35°C oraz z temperaturą minimalną > 15°C, > 18°C i > 20°C w Warszawie (Okęcie) w latach 1951-2009. Stwierdzono, że częstość każdego rodzaju dni wyraźnie wzrosła po roku 1990, a z wysoką temperaturą minimalną jeszcze bardziej wzrosła w XXI wieku. Chociaż częstość gorących dni i ciepłych nocy wzrasta, to okres ich występowania w ciągu roku nie wydłuża się. Nie ma również wzrostu najwyższej temperatury maksymalnej i minimalnej. Po roku 1990 wzrosła częstość fal upałów. Stwierdzono, że występowaniu bardzo wysokiej temperatury maksymalnej sprzyja cyrkulacja z sektora SE - S - SW, a wysokiej temperaturze minimalnej - cyrkulacja S i NE. Temperatura minimalna > 18°C na Okęciu przy cyrkulacji NE jest prawdopodobnie spowodowana napływem ciepłego powietrza znad miasta (prą miejskiej wyspy ciepła).

EN

The study focused on the number of days with maximum temperatures in three ranges, i.e. >25°C, >30°C and >35°C and with minimum temperatures also in three ranges, i.e. > 15°C, >18°C and >20°C, as recorded at the Okęcie weather station in Warsaw during the period 1951-2009. It was found that the frequency of each of these categories of days clearly increased after 1990 and that the frequency of high minimum temperature days increased again in the 21st century. Interestingly, while the frequency of hot days and warm nights increased, the extremely high values of maximum and minimum temperatures did not, nor did their seasons of occurrence change. What did increase was the frequency of heat waves after 1990. Very high maximum temperatures were more likely to occur in air circulating from the SE, S or SW and high minimum temperatures were more likely when the advection was from the S and NE. Days with minimum temperatures >18°C that occurred in the NE circulation might be linked to a movement of a hot island pushed from over the city center towards the weather station, which is located in the SW outskirts of Warsaw.