• Energy Research

Aim of the study: The city of Gdańsk faces changing climatic conditions that result in a higher frequency of extreme weather events. In response to the increasingly frequent appearance of flash floods, scientific research was carried out on changes in the probability of the occurrence of maximum daily precipitation in Gdańsk. The purpose of this paper is to show the role of hydrological research (science), decisions of local authorities and the engagement of residents in the process of adapting Gdańsk to climate change. Material and methods: The hydrological analysis was carried out using rainfall observations from the Gdańsk Rębiechowo station (1974-2021). Log-normal distribution was used as a statistical model for the precipitation probability distribution. To show the role of the city authorities’ decisions, the methodology developed and used by Gdańsk Water company for rainwater management was presented. To emphasize the importance of city residents in climate adaptation process, the methods adopted by city authorities to involve citizens in the advisory process are discussed, namely Civic Panels and the Gdańsk Climate Change Forum. Results and conclusions: The probability distributions of maximum precipitation for different periods were developed, showing a substantial increase of precipitation with a probability of p=1%. Consequently, changes were introduced in the rainwater management practices by the company Gdańsk Water. Being aware of rising flood hazard, Gdańsk City Hall has embraced a plan for adapting the city to climatic changes by 2030. The local authorities decided to involve citizens in the decision-making process. To this end, discussion panels were organized, and the Gdańsk Climate Change Forum was initiated.

Abstract Computational examinations of the flow field in an open channel having a single Backward--Facing Step (BFS) with a constant water depth of 1.5 m were performed. The e ects of the expansion ratio, and the flow velocity along the reattachment length, were investigated by employing two di erent expansion ratios of 1.5 and 2, and eight various flow velocities of 0.5, 1, 2, 3, 4, 5, 7.5 and 10 m/sec in the Computational Fluid Dynamic (CFD) simulations. Commercially available CFD software, ANSYS FLUENT, was used for calculations. The simulation outcomes were verified using experimental results. Moreover, analyses were performed by using two equation turbulence closure models, K-ɛ family (standard, RNG and realizable), and K-ω family (Wilcox’s and SST K-ω). The analyses have revealed that the reattachment length increases with an increase in the expansion ratio, the flow velocity and the Reynolds number. The results obtained for two expansion rates and eight di erent flow velocities have shown insignificant di erences between one turbulence closure model and the others. Furthermore, it was observed that both velocity and expansion ratios have an e ect on the reattachment zone size.

Aim of the study: The current paper aims to give a detailed evaluation and analysis of some extreme rainfall events that happened in the last decade in terms of spatial and temporal rainfall distribution, intensity rate and exceedance probability. Moreover, it examines the effects of each analysed aspect on the resulting flash floods in the study area. Material and methods: American Meteorology Society (AMS) in their glossary of meteorology divided rainfall intensity types into four groups (light, moderate, heavy, and violent). Also, for estimating the exceedance probability, Lognormal distribution was applied as a statistical model of the precipitation probability distribution function. Results and conclusions: Out of six episodes, five of the analysed events were classified as heavy rainfalls. However, the duration of heavy rainfalls was not more than two hours. Four events of maximum daily rainfall (for a 39-year dataset) were rated from 1 – 10% of exceedance probability. To conclude, the current study can be an initial step in modelling hydrological events in the study area and in the process of transforming precipitation into the outflows of urban basins in the future.