This study focuses on the in-depth assessment of the spatio-temporal variability of rainfall
in the Upper Medjerda Valley and its direct impact on the hydrological response of the
watershed. To this end, a rainfall database spanning from the hydrological year 1980/1981
to 2014/2015 was compiled, gathering the average time series of 16 rain gauges
strategically distributed across the studied basin. Missing data, inherent in any long-term
collection, were systematically reconstructed using a weighting method, thus ensuring the
integrity and continuity of the series. Subsequently, a rigorous statistical analysis was
conducted to detect significant breaks in each individual rainfall time series. Three
statistically robust tests – Pettitt, SNHT (Standard Normal Homogeneity Test) and
Buishand – were applied using XLstat software. These tests, combined with the detailed
calculation of specific rainfall indices, highlighted a pronounced alternation of wet and dry
episodes, characterized by occurrences of very high rainfall excesses, thus highlighting the
complex dynamics of the region's rainfall regime. The next step consisted of a spatial
interpolation of rainfall, carried out at different time scales: annual, monthly and seasonal.
Three geostatistical and deterministic interpolation methods were used to ensure robustness
of the results: the Theissen polygon, splines and ordinary kriging. The average rainfall
maps thus generated for the Upper Medjerda Valley then served as an essential basis for
the hydrological study. Finally, the study focused on examining the variation of
hydrological contributions, establishing their quantitative relationship with rainfall, and
assessing their crucial importance for the basin. This was achieved through the
implementation of the conceptual hydrological model GR2m. It has been shown that runoff,
and by extension, available water resources, constitute the direct and fundamental
hydrological response of the watershed to rainfall events, highlighting the close
interdependence between precipitation patterns and water availability.