Statistical Analysis of Extreme Dry Events in the Tunisian Sub-Humid Region Based on Probability Laws

Dry event duration analysis from series of daily rainfall observations in a Ghézala Dam catchment in Northern Tunisia, where the average rainfall is about 600 mm, was executed. The dry events are a series of dry days framed by a rainfall event. Rainfall events are defined as an uninterrupted series of rainfall days lasting at least a day having received a precipitation superior or equal to a threshold value of 4 mm d−1. The rainfall events are characterized by depth and duration. A correlation exists between these two parameters. Therefore, the rainfall depth per event is conditioned by the event duration. Respectively, the negative binomial and the geometric distribution best fits the dry event duration and the rainfall event duration. For the length of the climatical cycle, the incomplete gamma was found to be the appropriate distribution.