The IPCC climate models predict, for the Maghreb countries, lower rainfall and increased aridity. Current observations in the three countries of central Maghreb (Morocco, Algeria, and Tunisia) are not consistent with these predictions. To demonstrate this new trend, a detailed regional analysis of rainfall evolution is conducted. This investigation is based on the calculation of the reduced centered index and the chronological graphical method of processing information (MGCTI) of “Bertin matrix” type. The results show extreme variability of this parameter and the severe past drought (more intense for Morocco, in which the drastic conditions from the seventies are observed). The results also show the beginning of a gradual return to wetter conditions since the early 2000s in Algeria and Tunisia and from 2008 for Morocco (this trend is confirmed by recent agricultural production data in 2011/2012 and 2012/2013).

This study concerns the West African Sahel. The Sahelian climate is characterized by a long dry season and a rainy season which starts in June and ends in September–October. This latter season is associated with the process of oceanic moisture transfer to the mainland (the West African Monsoon). This movement is governed by an overall moving of the meteorological equator and its low-pressure corridor (Intertropical Convergence Zone, ITCZ) towards the north, under the effect of the attraction of the Saharan thermal depressions and a greater vigor of the anticyclonic nuclei. This study was conducted on 27 Sahelian climatic stations in three countries (Burkina Faso, Mauritania, and Senegal). The method used to determine the modes of this variability and the trends of rainfall is the chronological graphic method of information processing (MGCTI) of the “Bertin Matrix” and continuous wavelets transform (CWT). Results show a rain resumption observed in the recent years over the Sahelian region and a convincing link with the surface temperature of the Atlantic Ocean.

Des changements climatiques importants affectent une grande partie de notre planète. Les différents modèles prévoient ainsi une hausse probable des précipitations et des températures dans plusieurs régions du monde. Le présent travail analyse l'évolution des températures et des pluies enregistrées sur le littoral algérien pendant plus de quarante années. Les évolutions de ces deux paramètres témoignent des bouleversements climatiques subis ces dernières années par l'Afrique du Nord et le Grand Maghreb.

Cette étude porte sur le Sahel ouest-africain, qui fait la transition entre la zone sahélo-soudanienne assez arrosée et le désert saharien. Ce territoire s'étend sur 12 pays formant une bande longitudinale comprise entre 12 et 20° de latitude Nord. En Afrique de l'Ouest, six pays (Sénégal, Mauritanie, Mali, Niger, Burkina Faso et Tchad) appartiennent à cette région.Afin de déterminer la tendance pluviométrique dans trois pays de cette large bande territoriale (Mauritanie, Sénégal, Burkina Faso), on utilise la méthode graphique chronologique de traitement de l'information (MGCTI) de type "Matrice BERTIN". L'analyse des données pluviométriques montre une reprise des pluies depuis la fin des années 1980 ou les années 1990. Elle fait suite à la longue sécheresse sahélienne subie à partir de 1970.L'analyse des précipitations annuelles montre aussi une relation étroite avec la température de surface de l'océan Atlantique Nord (TNA), ainsi qu'un lien très fort avec l'énergie cumulative des cyclones tropicaux (ACE). Cette reprise des pluies, qui rappelle dans une moindre mesure les années de "vaches grasses" (cycle humide des années 1950-1960), est marquée cependant par une recrudescence sans précédent des inondations urbaines. Ces évènements sont imputables, d'une part, à l'intensification des pluies et, d'autre part, à un développement urbain mal maîtrisé.

IPCC climate forecast models, applicable to the Maghreb countries (Morocco, Algeria, and Tunisia), predict a decrease in atmospheric precipitation, greater variability, and an increase in aridity. In recent years, the entire region has been experiencing unprecedented climate upheavals. Climatic droughts have become increasingly severe and recurrent (drastically reducing water stocks). We are also witnessing a remarkable increase in temperatures and a greater frequency of heat waves. Faced with these new provisions, this territory (long considered an area of water stress) is now subject to very strong tensions, which have led to a greater demand for water and a decrease in supply. To understand the intensity of this “climate–water” crisis, we propose an analysis of this priority issue based on the evolution of precipitation over more than half a century of records. To determine precipitation trends and define rainfall cycles in these three countries, the graphical chronological method of information processing (MGCTI) of the “BERTIN Matrix” type is used. Annual precipitation totals from 29 stations were used for the MGCTI (chronological graphic method of information processing) for the period 1970–2023. These data come from the national meteorological networks of the National Meteorological Office (ONM) for Algeria, National Institute of Meteorology (NIM) for Tunisia, and National Directorate of Meteorology (DMN) for Morocco, and the from the websites of the National Climatic Data Center (NCDC) and “TuTiempo Network”. Monthly pluviometric totals from three stations, Dar El Beida (Algeria), Casablanca (Morocco), and Tunis (Tunisia), as well as the monthly NAO (North Atlantic Oscillation) and MOI (Mediterranean Oscillation Index) were used for the wavelet coherence method for the period 1970–2022. Data analysis shows that the entire region is subject to four extreme precipitation cycles (dry and wet). The last dry period was remarkably intense and led to a sharp increase in water stress throughout the region. An analysis of monthly precipitation from three stations (Casablanca, Dar El Beida, and Tunis) using the wavelet coherence method also highlighted a close relationship with the “NAO” and “MOI” circulation.

The French region adjacent to the Mediterranean basin is vulnerable to hydrological risks generated by convective precipitation in the form of heavy rainfall and conditioned by the configuration of the relief. These risks are driven by the increase in sea water temperature over the last half century, which itself has been more pronounced since 1990. The statistical analysis on the frequency of rainfall intensity in a 24 to 48 h interval, correlated with the NAO, WMOI and SSTMED indices shows a recrudescence of rainfall amounting to more than 100 mm, which leads to the genesis of floods and flash floods. Furthermore, there has been a higher frequency of floods and disasters in this period. The intensity of material and human damage recorded following such local Cévennes-type phenomena is also due to urban development and population growth.