engleski

Trends and variability in precipitation extremes along the eastern Adriatic

The paper should contribute to the knowledge of the eastern Adriatic extreme precipitation climatology within the LOP studies and the chapter WG3 Heavy rainfall, flash-floods and floods – topic 3.2a Quantitative precipitation estimation. The fact that precipitation change is highly variable regionally increased the need for more accurate regional and local precipitation change analysis to improve the analysis of impacts. Many of these impacts will be felt through extreme events. These increase a demand for determining from the observational record whether there have been significant changes in amount, frequency and intensity of extreme precipitation. Spatial differences in precipitation extremes trends indicated in earlier study based on centennial scale analysis at three locations at the eastern Adriatic, initiated further analysis based on denser network for the second half of the 20th century and the first decade of the 21st century. The spatio-temporal change in seasonal and annual precipitation is analysed for 23 Croatian rain gauge stations on the islands and the coast. Change in extreme precipitation conditions is investigated by trend analysis of seven indices of precipitation extremes proposed by World Meteorological Organization (CCl and CLIVAR). They are calculated using daily and multi-day precipitation data. The data series from the period 1953-2009 meet the criteria for calculating the indices. Trend for each station is estimated by means of Kendall’s tau method and the statistical significance is tested using the non-parametric Mann-Kendall test. The overall significance is assessed by Monte Carlo method. In order to evaluate the intensity and frequency of more rare events, the Generalized Extreme Value (GEV) distribution is applied to the time series of annual maxima of 1-day and 5-day precipitation amounts. Since the middle of 20th century a general decrease in annual precipitation is found, becoming stronger from north to south. Seasonal trends are found to be less homogeneous, both in direction and magnitude. Overall significant increase in the frequency of dry days is accompanied by slight change in the frequency of wet and very wet days. According to the daily intensity index, positive trends dominate over the analysed area. In spite the total precipitation decrease, part of annual precipitation amount coming from very wet days is increased. The 1-day and 5-day annual maxima showed large interannual variability. GEV distribution shape parameter has mainly negative values meaning that for the longer return periods the return values are likely to be overestimated. The estimates of 20-year return values calculated for 30-year moving periods indicate a strong influence of the upper outliers. An appearance of the upper outliers during the observed 60 years is discussed according to the 20-year return value.

precipitation extremes; trend; GEV distribution; eastern Adriatic

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