PROBABLE RAINFALL IN GDAŃSK IN VIEW OF CLIMATE CHANGE

Abstract

One of the manifestations of climate changes is the occurrence of a greater number of precipitation events, characterized by greater rain intensity that affects the economic stability of cities. Gdansk is an example of a city in which such events have occurred since the beginning of the twenty-first century. Due to the altitude differences in the area of Gdansk city (between –2 m and 180 m a.s.l.), the occurrence of extreme atmospheric precipitation almost immediately causes hydrological effects in the water network consisting of several streams of montane character, which flow eastwards from the plateau of the Kashubian Lakeland. Meteorological stations of the National Meteorological Service (IMGW-PIB) are located in the coastal zone (Port Polnocny/Northern Port, Świbno) and in the highest part of the city (the Rebiechowo airport). Because this is insufficient, the city of Gdansk has been expanding the local rain monitoring network since 2001, currently having reliable 10-year observation data sequences. The said network is operated by the Gdansk Water municipal company. Climate changes resulting in different characteristics of rainfall episodes in Gdansk naturally influence the determination of the probability of their occurrence. According to the rainfall model developed by Bogdanowicz and Stachy at the turn of the 20th and 21st centuries, at least 4 rainfall events lasting for over 8 hours in the last 17 years should be classified as a 100-year rain event. One of these extended the parameters of a 300-year rain event; whereas we asses the rain in the year 2016, when even 170 mm of rainfall was recorded on July 14, as at least a 500-year rain event. During this period, several-minute events were also recorded, which also exceeded the parameters of a 100-year rain event. The paper presents precipitation models for the region of Gdansk. Based on the maximum annual daily rainfall from Rebiechowo meteorological station from the years 1974–2017, an analysis of changes in precipitation values corresponding to certain probabilities of occurrence was conducted. An assessment was also made of the projected decrease in the value of precipitation in relation to hydro-technical constructions, road-engineering structures, and rainwater drainage systems in view of changing legal regulations, as well as the latest trends related to the management of rainwater.