Spatio-temporal analysis of short-term rainfall extremes in Croatia

Extreme rainfall events of short duration and their possible intensification in the future may induce large implications in the existing engineering structures and water risk assessment. In Croatia, the sub-daily time scale (6 hours and 12 hours) is used to select an appropriate threshold value to define yellow, green and red alarming categories in the Meteoalarm rainfall warning system. The study aims i) to provide the general climatology of short-rainfall extremes to analyse regional variability in precipitation extremes, and ii) to update the alarming rainfall thresholds in Croatia and to upgrade the alarming system from regional (presently 8 regions) to the county level (21 counties). The short-term (from 5 minutes to one hour) and sub-daily (from 2 to 24 hours) precipitation amounts are analysed in terms of their spatial and temporal characteristics. The study comprises the ombrographic station network of 56 stations, evenly distributed over Croatia, with datasets covering the period 1961-2019. For each duration, the Generalized Extreme Value (GEV) distribution is fitted to the annual-maxima precipitation amounts, employing both the stationary and non-stationary model. Spatial distribution of the corresponding 2, 5, 10, 25, 50 and 100 years return values shows a clear distinction between the continental and maritime regions for each duration of rainfall with a pronounced maximum in the northern Adriatic (Kvarner) region. The implications on the current rainfall thresholds in the alarming system and new proposals will be discussed. Additionally, the changes in characteristics of short-term precipitation extremes will be presented providing the climatological background for climate change adaptation activities and impact assessment in Croatia.