engleski

Extreme precipitation and related weather types over Croatia in the period 2001-2011

In this study a classification of weather types over Croatia for cases with extreme precipitation during the period 2001-2011 is done. Croatia is divided in six sub-regions, and the criterion for a daily extreme precipitation is different for every sub-region and is based on climatological return period of 5 or 10 years. The return value is defined as a value that is expected to be equalled or exceeded on average once every interval of time (T) (with a probability of 1/T). In this study te return values are estimated by fitting the Generalised Extreme Value Distribution (GEV) to the highest annual one-day precipitation amounts. The analysed data series cover the 1961-2010 time period. The maximum likelihood method was used for the estimation of three GEV parameters. In the 2001-2011 period, 57 extreme precipitation events were observed. The highest daily amount (188, 2 mm) was measured at the climatological station Lokve Brana, in the Mountainos part of Croatia, in winter. The extremes occur from May till December, and are most frequent in August (22 %) and September (22 %). From February till April, and also in July extremes were not recorded, and only one event with extreme precipitation was recorded in January. The South Adriatic (with islands) is a region with highest number of extremes according to climatological threshold. The clasification of weather types (developed by Poje, 1965) for cases with extreme precipitaton is done according to surface and upper-level pressure fields. The method is subjective, based on experience of forecaster. This approach is highly sensitive to minor differences in the route or location of synoptic systems in conjuction with the complex topography and sea-land exchange. Out of 29 weather types, 16 were detected during days with extreme precipitation. Even 65 % of detected weather types were connected with the influence of the depression. The most frequent (35%) weather type is C1 – eastern (front) sector of cyclone where the center is positioned westward of Croatia, most often over Gulf of Genoa and the North Adriatic. Upper-level pressure charts were analyzed to determine the prevailing large-scale flow that existed in the days with extreme precipitation. The most common flow regime is the SW, observed with a frequency of approximately 35 %. The SE flow also occurs with a relatively high frequency (26 %). The overview of synoptic situations in cases where daily amount of precipitation exceed values of 100-years return periods is done.

HPE; GEV distribution; weather types; Croatia

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