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Trend analysis of extreme and average rainfall in Crete

Renieri Styliani

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Summary

Climate change has affected the climatic conditions of the planet, so a large part of the scientific community studies this effect in different parts of the planet. For the island of Crete there is no clear picture of climate changes and the questions we want to answer are what is the trend of extreme rainfall events, if there is an increasing trend in the duration of extreme rainfall events and the number of extreme events.In this thesis a study was made of the trends of extreme and average values of rainfall on the island of Crete for the time period 1973-2011. For this purpose, the rainfall data of 49 meteorological stations from all over the island were used. For each station, precipitation indices and their trends were calculated as defined by the World Meteorological Organization expert group on Specific Climate Indicators (ET-SCI). Their indices and trends were calculated with the help of Climpact system software. Finally, plots of the indices in relation to time were created for the statistically significant stations and maps illustrating the trends of these indices in relation to the significance per decade.By studying the results of the graphs, the average values of the trends and the maps in combination, we were led to various conclusions. The average annual rainfall was estimated at 813mm, the rain heights decrease from north to south and from west to east. Also, based on the statistically significant trends, it seems that the average annual rainfall and the duration of intense and extreme rain events have decreased, while the extreme phenomena show increasing intensity. An increase in the amount of rain per day of precipitation and the maximum amount of rain for one-day, three-day and five-day precipitation was also observed, that is, more rainfal precipitates in a short period of time.Due to the peculiarity of the soil and the individual climate types that prevail on the island, the above conclusions differ for some areas of Crete. More specifically, in the prefectures of Chania and Rethymno, the duration of intense phenomena seems to have decreased and the height of extreme rainfall has increased, while in the southern part of the prefecture of Heraklion, where all the indices that calculated for the stations in that region show a downward trend, drought phenomena are observed .Finally, the average annual rainfall in the area of ​​Crete showed a downward trend , for the period 1973-2011, which is in agreement with the decreasing rainfall of the Greek region according to the literature, while the trends of extreme phenomena, although locally mixed, appear an average increase.

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