engleski

Trends and variability in precipitation extremes along the Eastern Adriatic

The spatial-temporal change in seasonal and annual precipitation during the second half of the 20th century and the first decade of the 21st century is analysed along the eastern Adriatic 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 for 23 rain gauge stations on the islands and the coast. 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.

trends; variability; extremes; Adriatic

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