Historical streamflow droughts on the Vistula River in Warsaw in the context of the current ones
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Szkoła Gółwna Gospodarstwa Wiejskiego, Instytut Inżynierii Środowiska
Szkoła Główna Gospodarstwa Wiejskiego, Instytut Inżynierii Środowiska
Ewa Kaznowska   

Szkoła Główna Gospodarstwa Wiejskiego, Instytut Inżynierii Środowiska
Submission date: 2020-11-12
Final revision date: 2021-03-01
Acceptance date: 2021-03-19
Publication date: 2021-05-04
Acta Sci. Pol. Formatio Circumiectus 2020;19(4):53–81
Aim of the study:
The aim of the study was to investigate the size of the current low flows on the Vistula River in Warsaw in order to find out whether the alarming extreme low water levels observed correspond to extremely low flows and show any tendencies.

Material and methods:
The hydrological data starting from 1920 at gauging stations: Warszawa, Warszawa-Bulwary, Warszawa-Nadwilanówka, were analyzed. The non-parametric Mann-Kendall test at the significance level α = 0.05 was used to establish characteristic of the streamflow droughts.

Results and conclusions:
Over the last 20 years, deep streamflow droughts occurred in the following years: 2003, 2007, 2012, 2015, 2019 and 2020. Until 2019, the lowest absolute minimum from 2015 at the Warszawa-Bulwary gauging station was not exceeded. However, when considering the water levels at the Warszawa-Nadwilanówka gauging station, the absolute minimum was exceeded by 9 cm (state 102 cm) in September 2020. Minimum annual flows oscillate around the mean value and even show a statistically insignificant tendency to increase. However, the minimum water states are clearly decreasing and it is a statistically significant change (α = 0.05) caused by the deepening of the riverbed in the Warsaw section, and not by reducing the water supply. In the period 1951-2019, there was not observed the increase in the duration or deepening of the deficit volume of streamflow droughts. The summer streamflow droughts in 2019 and 2012 observed in the last decade did not reach a size similar in terms of duration and deficit volume to the average streamflow drought determined for the 1951-2000 period.