Abstract
Several episodes of extreme precipitation excess and extreme precipitation deficit, with considerable economic and social impacts, have occurred in Europe and in Poland in the last decades. However, the changes of related indices exhibit complex variability. This paper analyses changes in indices related to observed abundance and deficit of precipitated water in Poland. Among studied indices are maximum seasonal 24-h precipitation for the winter half-year (Oct.–March) and the summer half-year (Apr.–Sept.), maximum 5-day precipitation, maximum monthly precipitation and number of days with intense or very intense precipitation (respectively, in excess of 10 mm or 20 mm per day). Also, the warm-seasonal maximum number of consecutive dry days (longest period with daily precipitation below 1 mm) was examined. Analysis of precipitation extremes showed that daily maximum precipitation for the summer half-year increased for many stations, and increases during the summer half-year are more numerous than those in the winter half-year. Also, analysis of 5-day and monthly precipitation sums show increases for many stations. Number of days with intense precipitation increases especially in the north-western part of Poland. The number of consecutive dry days is getting higher for many stations in the summer half-year. Comparison of these two periods: colder 1961–1990 and warmer 1991–2015, revealed that during last 25 years most of statistical indices, such as 25th and 75th percentiles, median, mean and maximum are higher. However, many changes discussed in this paper are weak and statistically insignificant. The findings reported in this paper challenge results based on earlier data that do not include 2007–2015.
Highlights
According to the Clausius-Clapeyron law, there is more room for water vapour in the warming atmosphere; potential for intense precipitation grows
Heavy precipitation indices are projected to increase in all regional domains (Hay et al 2016), while a strong increase in dry-day frequencies is projected over land regions, which are experienced by problems with scarcity of water, e.g. in the Mediterranean region (Polade et al 2014)
Comparison of two periods: colder 1961–1990 and warmer 1991–2015, revealed that, during the last 25 years, most statistical indices, such as 25th and 75th percentiles, median, mean and maximum were higher. This holds for the maximum 5-day and maximum monthly precipitation total
Summary
According to the Clausius-Clapeyron law, there is more room for water vapour in the warming atmosphere; potential for intense precipitation grows. Frequency and intensity of heavy precipitation events has likely increased in North America and Europe, as a result of anthropogenic forcing, which leads to an intensification of the water cycle. The so-far change-detection exercises do not show a ubiquitous and consistent signal in extremely high precipitation at the continental (European), regional or national levels. Updating change-detection efforts in order to interpret the climate-change signal is of considerable importance and interest. Investigation of observed changes is an important task to enable better interpretation of possible future trends. Increase of the extreme abundance of water has potential impacts, including floods, erosion, flash floods and inundation.
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