## 4 Results  
Firstly, both cities were analysed in terms of historical flood events. Numerous sources, dating back to the early 20 th century, indicate that both areas have experienced flash floods and riverbank overflows caused by prolonged and heavy rainfall. Additionally, Wyszkow, due to its location within a meandering river valley, is periodically affected by floods resulting from ice blockages that obstruct the river's flow. Recent data from emergency responses to urban flooding caused by heavy rainfall have provided valuable insights into flood-prone areas, highlighting specific locations and occurrences of interventions concerning critical infrastructure and residential zones. The average soil sealing within urban zones is 38.6% in Bielsko-Biala and 47.1% in Wyszkow (Figures 5 and 6), while the total area of sealed soil accounts for 35.8% and 36.9%, respectively. The map illustrating the spatial distribution of impervious surfaces highlights an ongoing suburbanisation process, with land development expanding towards the outskirts. This expansion has resulted in a notable increase in impervious surfaces, even in areas that were previously uninhabited, such as uphill and forested regions in the southern part of Bielsko-Biala. In Wyszkow, the highest levels of imperviousness are observed in the northern part of the city, where industrial and service facilities, including large-scale halls, are concentrated. Furthermore, residential areas are noticeably sprawling towards the riverbanks, exacerbating the risk of flooding in these zones. This trend underscores the necessity of strategic urban planning to address the challenges posed by increasing imperviousness and associated hydrological risks. Figure 5: The spatial distribution of soil sealing in Bielsko-Biala City. The flood hazard in Bielsko-Biala, resulting from riverbank overflow during extreme precipitation events with a 1-in-100-year return period, is illustrated in Figure 7. This is accompanied by an analysis of the depth of non-drained urban basins, presented in Figure 8. Comparable data are provided for Wyszkow in Figures 9 and 10, respectively. In addition, for Wyszkow, spatial data on intervention sites related to local flooding events, as recorded by the Firefighter Department, are also incorporated to enhance the assessment of flood-prone areas. This representation highlights both the areas within the city susceptible to flash flooding and the regions near riverbanks vulnerable to river flooding. In Bielsko-Biala, the areas prone to river flooding cover approximately 0.84 km\({}^{2}\) and are primarily concentrated near the Biala River. The non-drained urban basins in Bielsko-Biala encompass an area of approximately 0.67 km\({}^{2}\), with buildings located within these basins facing significant flooding risks during heavy rainfall due to water accumulation in urban depressions. In comparison, the city of Wyszkow appears to face greater flooding risks, both from flash flooding and water accumulation in local depressions, which span an area of 0.93 km\({}^{2}\), as well as from river flooding. The area threatened by river flooding in Wyszkow extends over 3.88 km\({}^{2}\), underscoring considerable vulnerability to hydrological risks. A detailed analysis of non-drained urban basins, areas prone to river flooding, and intervention points identified by local firefighters provides precise locations where action is required. These measures may include small-scale nature-based solutions or more advanced technical infrastructure designed to mitigate river flooding and its associated impacts, depending on the areas at risk and the depth of potential flooding within the basins. Figure 6: The spatial distribution of soil sealing in Wyszkow City. Figure 8: The localisation and depth analysis of potential non-drained urban basins in Bielsko-Biala City. Figure 7: Flooding threats in Bielsko-Biala City include risks from non-drained urban basins as well as overflow from riverbanks.