Severity-duration-frequency analysis of droughts and wet periods in Greece

There is an escalation in the frequency and severity of extreme events due to a number of environmental and/or anthropogenic factors. Droughts and exc eptionally wet periods are regional phenomena, which are considered as majo r environmental extremes, especially in semiarid regions of the world, such as Greece. The development of severity-duration-frequency (SDF) relationsh ips of droughts and wet periods over Greece is important in contemporary hy droclimatic and agroclimatic design and planning in the country. The Palmer Drought Severity Index (PDSI) is used for a quantitative description of dr oughts and wet periods. Statistical tests and visual inspection indicate th at the EV1 (Gumbel) frequency distribution fits satisfactorily all the iden tified durations of droughts and wet periods, respectively. Moreover, the S DF curves show that decreasing frequencies (i.e. increasing recurrence inte rvals) correspond to increasing severities of droughts and wet periods, res pectively. The developed SDF relationships are used to produce tables and i soseverity maps of Greece for each identified duration and all the selected return periods or frequencies, which constitute an essential aid for desig n purposes. The results of the study indicate that there is a decreasing pa ttern of the severities of droughts and wet periods from west to east and t hat, for similar durations and return periods, the wet spells are, in gener al, more extreme than droughts in Greece.