Due to its geographical location, Algeria is characterized by high spatiotemporal rainfall variability. In this study, data from 69 rain gauges located in representative humid, semiarid, and arid Mediterranean basins in northeastern Algeria were analyzed from 1970–2007 on a monthly scale using continuous wavelet analysis and hierarchical cluster analysis with the aim of regionalizing the rainfall patterns. The analysis shows that northern Algeria (Cluster 1), which has a humid climate, is dominated by periodic annual fluctuations in the 8–16-month band. This mode explains most of the total variance, with a contribution between 25 and 60%. In the Cluster 2 and Cluster 3 regions, the climate varies towards aridity (humid to arid from north to south), and the climate is dominated by long-term periodic phenomena characterizing multiannual fluctuations of 64–128 months to decadal periods greater than 128 months, which explains why the total cumulative contribution exceeds 50% of the total variance. In addition, the regional analysis of the isolated spectral bands of the 3–6-month (3 clusters), 8–16-month (3 clusters), and 1–3-year (4 clusters) scale-average variance revealed, globally and for the different regions, a long period of drought that was most pronounced during the 1970s, 1980s, and 1990s, whereas the wet years were marked by fluctuations that exceeded the 95% confidence level during the study period, with a very remarkable tendency towards wet conditions, particularly since the late 1990s. The obtained results can assist decision-makers in better sustainable development practices, especially in the fields of water resources, agriculture, and energy.
