Estimation of droughts and floods occurrences in central Poland under climate change scenarios

Droughts and floods are the most hazardous disasters to affect the landscape and human communities. Climate change is increasing their frequency and intensity all around the world. In this research, we study the impact that climate change in central Poland (Toruń) is having on the frequency of meteorological droughts and risk of floods occurrence in the region, based on the standardised precipitation index (SPI) as one of the most common and effective indices. Although the SPI was developed for monitoring droughts, previous studies have shown that it can also be applied to recognise wet and normal conditions. Therefore, in this study, we attempt to determine the relationship between SPI values and high flood risk. First, by an average mean ensemble of several general circulation models (GCMs), precipitation for a future period (2026–2100) in Toruń was projected under two climate change socio-economic pathway scenarios (SSPs), SSP1-2.6 and SSP5-8.5. Then, based on the projected precipitation for the future period, the SPI values were calculated. The results indicated that, in general, the precipitation in the study area will increase for scenarios SSP1-2.6 and SSP5-8.5.

Estimation of future meteorological drought based on SPI calculation showed that the frequency of the “Extremely dry” (SPI ≤ ˗2.0) and “Severely dry” (˗1.50 ≤ SPI < ˗2.0) categories will decrease under scenarios SSP1-2.6 and SSP5-8.5, while the frequency of the “Moderately dry” category (˗1.0 ≤ SPI < ˗1.50) will increase for scenarios SSP1-2.6 and SSP5-8.5 relative to the historical reference period (1991–2014).

Estimation of flood risk occurrences in the future period based on SPI values showed that the frequency of “Extremely wet” (SPI ≥ 2.0) will increase for SSP1-2.6 and SSP5-8.5, excluding the future periods 2076–2100 in SSP1-2.6 and 2026–2050 for SSP5-8.5. The frequency of “Very wet” (1.50 ≤ SPI < 2.00) will increase for both scenarios. It is also expected that frequencies of other categories including “Moderately wet” (1.00 ≤ SPI < 1.50), and “Near normal” (˗0.99 ≤ SPI <1) will slightly decrease for both scenarios.

To conclude, a decrease in the frequency of “Extremely dry” and “Severely dry” categories and an increase in the frequency of “Extremely wet” and “Very wet” showed that the occurrence of floods is more probable than droughts in the study area in the future period.

The work was supported by the National Science Centre, Poland project No. 2020/37/B/ST10/00710.