The characterization of droughts and dry spells in Northern Tunisia based on the analysis of daily rainfall series

Study region: The Ichkeul lacke basin, Northern Tunisia. Study focus: In semi-arid regions, the characterization of dry spells and drought severity in order to establish diagnoses and prognoses that help water resources management is crucial. Therefore, the aim of this study was to analyze the frequency of extreme droughts and evaluation of extreme dry spell behavior some distingue rainfall thresholds value to determine susceptibility to the potential risk of Ichkeul lacke basin, by the alternating wet/dry spell method and the magnitude of droughts as a classification of the dry event duration with the accumulated rainfall depth per event and the statistical return period for the maximum dry event duration. New hydrological insights for the region: Daily precipitation data collected at seven rain gauges in the basin were analyzed and used. Dry days were defined as having less than a threshold value of accumulated precipitation. Various values of the precipitation threshold were investigated. Analysis point out that dry spells occur randomly during the rainy season. The longest dry spells associated with various statistical recurrence periods are derived on the basis of the fitted Generalized Extreme Value (GEV) distributions. An extreme case (meteorological droughts) was analysed. From the drought return period analysis, the 1 September 1987 drought was found to be the most extreme with a 127-yr return period. The maximum number of seasonal dry events observed is inversely proportional to the threshold value. Longest observed in rainfall event duration is invariant to the rainfall threshold and displays 13 days. This study provides the foundation data for analyzing Ichkeul’s vulnerability to droughts.