engleski

Short-term heavy rainfalls and their causes, Istra, Croatia

The area of the Istra peninsula at the Croatian eastern Adriatic coast with its few small rivers belongs to the Adriatic catchments. Floods that appear as a consequence of heavy rainfall harm mainly agricultural valleys. This paper deals with the investigation of magnitude (design parameter) and causes (forecasting input) of rainfall extremes over this region (coastal and inland sites). The appearance of rainfall extremes during the year and their connection with the pattern of the maritime or continental annual course of precipitation is analysed. Extreme value analysis (GEV) according to Jenkinson has been applied to rainfall maxima for intervals t up to two hours that are relevant for surface drainage. Estimates of maxima that can be expected for different return periods T are important input data in design calculations of hydro-technical infrastructures in order to reduce climatic risk. According to the coefficient of variation the difference in spatial variability of short-term maxima is indicated. The calculated values of the parameters R0, k and  of the Jenkinson distribution according to the 1962-2002 data series are presented for two stations (Pula - coastal and Abrami - inland) and intervals of 10-, 20-, 30-, 40-, 50- 60- and 120-minutes. The expected maxima RtT, namely the design values for each interval (t) and desired return periods (T) were calculated. This has been done for the return periods of 10, 20, 50 and 100 years, namely for those supposed not to be exceeded with the 90%, 95%, 98% and 99% probability. Weather types causing rainfall maxima over threshold for all observed intervals have been determined according to Poje classification and the analysis for the Northern Adriatic. The basic characteristics of weather types are presented by surface fields of air pressure and in some cases at 850 hPa. Frequency of weather types was calculated for two locations, at the coast and in the central part of the Istra peninsula. Three episodes of heavy rainfall followed by floods are analysed in more detail.

short-term heavy precipitation; extreme value analysis; weather types; Istra peninsula; Croatia

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