THE DEPENDENCE OF THE ANNUAL TOTAL ON THE NUMBER OF RAIN-SPELLS AND THEIR YIELD IN THE MEDITERRANEAN

Rain-spells are a key parameter for examining the variation in rainfall amounts, especially in arid and semi-arid areas. A rain-spell is defined as a period of consecutive days with rainfall above a certain determined Daily Rainfall Threshold (DRT). Two different seasons or two stations may have the same average TOTAL, but different synoptic conditions are the cause for the differences in their Number of Rain-Spells (NRS) their Rain-Spells Yield (RSY) or both. The present study examines whether a season is drier/wetter according to its length, or whether it depends on the NRS in 41 Mediterranean stations. It analyses the relationships between dry/wet seasons and various elements of the rain-spells. These objectives are analysed both at a basin level of the entire Mediterranean, and at a station level. The main conclusions at the basin level are that precipitation amounts are not related to the length of the seasons, and therefore, a Short or a Long season can be either Dry or Wet. The significant positive correlation between the TOTAL and the annual NRS that was found indicates that a Dry season tends to have Few rain-spells and a Wet season tends to have Many rain-spells. At the station level of most stations, a Dry or Wet season is caused mainly by changes in the RSY and less so by changes in the NRS. This tendency is more evident in the southern Mediterranean. Furthermore, Wet seasons are characterized by an increase in the number of Long rain-spells (longer than three days) and mainly in the RSY of these spells. These conclusions may serve to characterize the rainfall regime under any scenario due to a climatic change.