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The Maghreb countries located in North Africa are strongly impacted by floods, causing extended damage and numerous deaths. Up to now, the lack of accessibility of river discharge data prevented regional studies on potential changes in flood hazards or the development of regional flood frequency estimation methods. A database of daily river discharge data from 55 basins located in Algeria, Morocco and Tunisia, has been recently compiled, with on average 32 years of complete records over the time period 1970-2017. A peaks-over-threshold sampling of flood events is considered, first to detect trends on the annual frequency and the magnitude of floods. The trend analysis results indicated no significant changes in flood frequency nor magnitude, with only a few spurious trends detected in cases of isolated extreme or clustered events. Then, two regional estimation methods for flood quantiles were compared, based either on spatial proximity or catchment characteristics. The regional estimation from multiple catchment characteristics (including soil types, land use, elevation, geology, extracted from global databases) was performed comparing two multiple linear regression methods, Stepwise regression and Lasso regression, and two machine learning algorithms, Random Forests and Support Vector Machines. Results indicate a better performance of the regional estimation of flood quantiles with catchments characteristics than with spatial proximity, with a mean absolute error in cross-validation close to 40%. These encouraging results open the perspective of operational applications of these methods, in particular by increasing the number of basins considered.

This work focuses on the contribution of the documentation of the fluvial sedimentary archive in the study of the contribution of rainfall and large dams in the decline of sedimentary inputs of the Cheliff Wadi at the outlet. Therefore, three sediment cores, taken in the lower Cheliff valley, were studied through the paleohydrological approach. Such an examination aims, on the one hand, to establish a chronology of depositional accumulation and, on the other hand, to evaluate the ability of the information incorporated in the sedimentary archive to transcribe the evolution of the hydrosedimentary signal and the fluctuations of the controlling factors.The results reveal: a strong variation in the granulometric distribution of the deposits and a progressive decline in the progressive decline in the rate of sediment accumulation. Thus, the upper part of the core is mainly made of particles belonging to the fine granulometric class that have accumulated with fine that accumulated with an average rate of about 1.31 cm / year. Contrary to the deposits composed of a succession of coarse and fine sedimentary layers, and showing a rhythm of accumulation much more superior, whose value is evaluated to 16 cm/year. However, the fluctuations observed in the granulometric composition and the accumulation rate of the deposits correlated strongly with the evolution of the rainfall signal and/or the multiplication of the number of large dams. Indeed, relatively coarse deposits and a higher accumulation rate correspond to the wet period before 1980. Then, the decrease in rainfall was accompanied by a longer accumulation rate and deposits composed mainly of fine particles. In addition, the recently built dams, bringing the outlet of the watershed closer and closer, have a drastic effect on the deposition process.Key words: Sedimentary archive, paleohydrological approach, Cheliff, rainfall, granulometric profile.

The water deficit of recent decades has negatively affected agricultural production as well as surface and underground water resources in Algeria. To assess he impact of the future climate, for (2020-2060) and (2060-2099), on the water resources in several basins, we used analysis of historical average flows and compare them to those that could result from changes in temperature and rainfall. The methodology is based on the GRM2 model with the development of prospective climate change scenarios for both horizons. To study the impact of climate change on water resources, we used the climate projections of the CORDEX Arica model with the two pessimistic (RCP 8.5) and optimistic (RCP 4.5) scenarios. The results of the simulations of the future scenarios showed that the historical seasonality of precipitation fades away for the RCP 4.5 and 8.5 scenarios, and gives way to a more irregular pattern where rainfall is abundant in late autumn and spring. Furthermore, this interannual evolution of the RCP scenarios indicates an increase in extreme events during these periods, thus increasing the risk of flooding considerably. The results of the simulations of the future scenarios showed a clear decrease of the flows. This decrease varies, for the seven sub-basins composing the plain, between 17 and 50% for the near future and the RC4.5 scenario. For scenario 8.5, the decrease varies between 37 and 55%. For the distant future (2060-2099), the reduction in flows varies between 27 and 45% for the near future and the RC4.5 scenario. For scenario 8.5, the reduction varies between 40 and 62%. We note that the basins which drain part of the Blidean Atlas present lower projected reductions for the future compared to the other basins of the plain. The two stations of the first two are located at the entrance to the plain.

Maghreb countries are strongly impacted by floods, causing twice as many deaths as in southern European countries in recent decades. However, due to the lack of data accessibility, there are no studies to analyze whether the frequency or intensity of floods are changing at the regional scale. In this work, a recent database of daily river discharge data from 58 basins located in Algeria, Morocco and Tunisia with on average 32 years of complete records over the time period 1970-2017 is considered to analyze the evolution of floods. A peaks-over-threshold sampling of flood events is considered, to detect trends on the annual frequency and the magnitude of floods. The results illustrate the complexity of conducting trend detection in a context of high inter-annual variability, with spurious trends detected in several cases due to isolated extreme events. Overall, few statistically significant trends are detected on the intensity of floods but an increase in flood frequency is detected in one-third of the basins. The results are interpreted in relation to land-use change, river regulation by dams and reservoirs, and climatic change. Recommendations concerning the use of frequency analysis approaches on floods in this region are given.