Modeling the reliability of storm water drainage systems encounters a number of methodological difficulties, especially in the selection of a reliable rainfall scenario. Many methods for creating reference hyetographs are described in the literature. The aim of the work was the analysis of the shapes of local precipitation hyetographs and the verification of the reference shapes of rainfall hyetographs used for the drainage systems designing and modeling its operation in Poland (Euler type II and DVWK models). The research material was represented by historical records of rainfall data from the measuring station located in Jelenia Góra (Poland). Rainfall were grouped due to the similarity of physical features, using various methodologies: Huff, cluster analysis using the Ward and k-means methods. The k-means method proved to be especially useful for selecting precipitation in terms of shape hyetographs. The statistical analysis of the similarity of the rainfall hyetograph shapes was performed within the separated genetic clusters, based on the parameters of mass distributions and unevenness over time. The comparative analysis allowed for the positive verification of the Euler type II and DVWK models for the tested station.

Stormwater drainage from urbanised areas has gained importance due to progressing land surface sealing and climate change. More frequent extreme rainfall events lead to overloaded drainage systems and flash floods, particularly in industrial zones experiencing rapid development. The study analysed the sewage system operation in the Special Economic Zone (SEZ) in Lower Silesia, Poland to assess the impact of climate-induced rainfall changes. Three rainfall scenarios were used: model rainfall using historic rainfall intensities, model rainfall using actual intensities, and real precipitation recorded in June 2022. Findings indicate that climate change has negatively affected the stormwater drainage system, resulting in increased overloads and flooding. Particularly, the II scenario showed a significant rise in rainwater inflow to retention reservoirs by 53.1% for ZR-1 and 44.5% for ZR-2 (compared to the I scenario). To address these issues, adaptations are needed for increased rainwater flows, including additional retention facilities, blue–green infrastructure, or rainwater harvesting for the SEZ needs.

One of the most important problems while modeling stormwater drainage systems is the choice of rainfall scenario, which will take into account the real rainfall distribution over time. This problem is particularly significant due to the climate change observed in recent decades, manifested, among others, in the increase in the precipitation intensities or changes in their structure. Taking into account these forecasts is essential to safely design sewer systems and their proper operation. The work aims to verify the Euler type II standard rainfall used so far to model sewage systems in Poland and to develop the forecasted form of this pattern in the perspective of 2050. Precipitation data from measurement stations in Wrocław were used as research material. The prediction model of maximum rainfall amounts allowed to determine the forecasted increase in intensities of short-term rainfall (for the occurrence frequencies recommended by Standard EN 752:2017 for the dimensioning and modeling of sewage systems). On this basis, model hyetographs forecasted for 2050 were prepared for Wrocław. Their choice—as a future rainfall load in hydrodynamic modeling—will allow one to meet the requirements for the frequency of flooding occurrence from sewer systems and their safe operation over several decades.

Standards for the dimensioning and assessment of reliable operations of area drainage systems under conditions of climate change

In recent years, the issue of rainwater drainage has become particularly relevant due to increasing urbanization and climate change. The increasing frequency of extreme rainfall leads to urban flooding and infrastructure damage. These events sometimes also lead to legal consequences for designers and contractors of drainage systems. The design of these systems in Poland has encountered difficulties due to the lack of a reliable, publicly available method for determining the reliable rainfall intensity. The study aims to present the PMAXTP atlas made available by the Institute of Meteorology and Water Management – National Research Institute (IMGW-PIB) as a tool for the precise determination of the maximum rainfall characteristics for a specific duration and probability of exceedance for any location in Poland. IMGW-PIB plans to update the PMAXTP atlas every 10 years to reflect climate changes and the increasing frequency of intense rainfall. The publication also presents computational examples for applications in engineering practice. Using this tool in design practice will allow for the safe and effective design of drainage systems that will be resistant to climate change and extreme weather conditions.