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Algeria has experienced catastrophic floods over the second half of the twentieth century, causing many deaths and extensive material damage. This study was conducted to find a suitable event-based rainfall-runoff (RR) model for semi-arid conditions, where continuous data are not available in all regional basins. The study compared, based on data availability, the SCS-CN model based on the antecedent moisture conditions (AMC) and four modified SCS-CN models incorporating antecedent moisture amounts (AMA) in order to find the best model to reproduce the flood hydrographs in two catchments. The modified models were predominant over the SCS-CN method. Nonetheless, the Singh et al. (Water Resour Manag 29:4111–4127, 2015. https://doi.org/10.1007/s11269-015-1048-1 ) model (M4) and the Verma et al. (Environ Earth Sci 76:736, 2017a. https://doi.org/10.1007/s12665-017-7062-2 ) model (M5) were superior and demonstrated more stable structures. Coupled with the Hayami routing model, the models showed promising results and were able to reproduce the observed hydrographs’ shape. However, it was impossible to choose the preferred model since they each excelled as to a criterion. Therefore, the corresponding outputs were combined using the simple average (SA) method and the weighted average (WA) method. We found that the WA method showed better results in the two catchments and allowed a more accurate prediction according to the performance criteria.

This work aims to identify the potential groundwater recharge zones in the Mitidja plain (north Algeria) using the multi-criteria approach. The analysis was based on the use of a geographical information system (GIS) and remote sensing to establish eight thematic maps, weighted, categorized and inserted, that allowed us to establish the potential zones’ map for groundwater recharge. Three potential groundwater recharge classes were defined corresponding, respectively, to low (26%), moderate (47%) and high (27%). The best groundwater potential zones are situated in the piedmont of the Blidean Atlas (the south of the study area), precisely, upstream near to wadis (wadi El Harrach, wadi Djemaa, wadi Mazafran) and the western aquifer limit, where the hydrogeological units are formed by the alluvium formation which is characterized by high hydraulic conductivity, high water flow, low slope, low drainage, low quantity transported sediments and good water quality. The obtained results, in this work, describe the groundwater recharge potential areas and supply information for a suitable mapping and the management of aquifer resources in the study area.

This study aims to estimate hydrological drought risk using probabilistic analysis of bivariate drought characteristics to assess both past and future drought severity and duration in three basins located in the widest karst massif of northern Algeria. The procedures entail: (1) identification of extent of meteorological drought that could trigger corresponding hydrological drought through their characteristics; (2) assessment of future risk of extreme drought according to two emission scenarios of the representative concentration pathway (RCP 4.5 and 8.5); and (3) estimation of drought return periods using bivariate frequency analysis and investigation of their future change rates under climate change. Hydrological droughts were computed by using the bias-corrected future climate projections from nine global climate models downscaled using the Rossby Centre Regional Climate model (RCA4), and GR2M hydrological model. The analysis revealed a connection between meteorological and hydrological drought occurrences and the response time depended on the memory effect of the considered basin. We also found strong consensus between past drought event return periods, determined by bivariate frequency analysis, and those determined by climate models under RCP8.5 scenario. Finally, in regards to drought return periods (10, 50 and 100 years), the risk of extreme drought recurrence in the future has been projected to be larger than the reference period.

Algeria shares similarities with other countries of the world facing destructive floods. The need to understand changes in the intensity, frequency and severity of floods is critical for reducing significant social, economic, and environmental implications. In this study, flood indicators derived from annual maximum series and peak over threshold series were analyzed using Mann−Kendall trend analysis and linear regression analysis. Several studies in northern Algeria found decreasing trends of annual precipitation. However, precipitation could not explain most flood indicator trends found in our study. A general decreasing annual and seasonal trends of flood indicators were detected in the wadi Cheliff Basin. This result is partly due to decreasing precipitation and partly due to the construction of dams which have significantly altered flood processes. Increasing trends were found in the Mina Basin, which could be explained as the result of increases in urban area and decrease in soil moisture content before the occurrence of floods. Conversely, there was no dependency demonstrated between significant changes and spatial scales for these flood indicators. That is to say, human impacts and climate variability likely constitute the main factors causing increasing or decreasing flood trends.

The Cheliff–Zahrez plains in Algeria are known for their fertility and agricultural production. The water deficit of the last decade has had a negative impact on agricultural production due to the scarcity of surface and underground supply resources. This paper sheds light on the weather, drought risk concerning crop irrigation in wheat yield cases. The methodology was the standardized precipitation index, which helps to identify a drought risk assessment model based on moderate frequency maps carried out by the geographic information system. Over the study area, 65 rainfall stations are considered, each with 41-year measurement period (1970/2010). According to the results, this basin has generally periods of humidity and drought with a tendency towards drought. The spatial distribution analyses of drought incidence in the derived Cheliff–Zahrez Basin (standardized precipitation index) and annual rainfall have shown that since 1970, the basin has experienced below-average rainfall, particularly in the central and northern regions. Various maps from 1970 to 2010 show that the basin is characterized by high spatial variability in rainfall from one station to another with the north and northeast sub-basins being much more sensitive to agricultural drought. Generally, the sub-basin in the western zone has a moderate vulnerability. The southern zone is characterized by moderate drought (less frequent in the basin). The drought hazard index map from 1970 to 2010 showed that the moderate and severe drought classes cover an area of 93.34% and 3.66%, respectively, with drought occurrence probabilities of 15 to 22.5% and 22.5 to 30%. The correlation is significant in the order of 70% to 75% between dry spells and wheat production.

In last decades, the impact of climate change started to appear in the semi-arid regions of the Mediterranean Basin. The severity and frequency of drought events in Northwestern Algeria have affected water resources availability and agriculture. This study aims to evaluate the temporal evolution of drought events characteristics, such as drought duration, frequency and severity, of the Beni Bahdel Dam catchment, Northwestern Algeria. Drought characteristics have been derived from the Standardized precipitation index (SPI) computed for the period from 1941 to 2100 using precipitation data from observations and simulations of the regional climate model RCA4 (Rossby Centre Atmosphere model, version 4). The RCA4 model was forced by the global circulation model MPI-ESM-LR under two Representative Concentration Pathways (RCPs) scenarios. The ability of the model simulations was firstly assessed to reproduce the drought characteristics from observed data (1951–2005). Then, future changes in drought characteristics over the twenty-first century were investigated under the two scenarios (RCP4.5 and RCP8.5). Results show an amplification of drought frequencies and durations in the future under the RCP8.5 scenario.

An analysis of rainfall and hydrometric regimes was carried out over the period from 1968 to 2013 on the Cheliff basin situated in the west and the Medjerda basin in the east of Algeria. The Mann-Kendal and Pettitt tests have shown significant downward trends for rainfall, about 30% for the Cheliff basin, and 36% for the Medjerda basin, and about 61% and 43% for the flows at the level of the Cheliff and Medjerda basins, respectively. The continuous wavelet method, used during the study period, has shown three major discontinuities from the wavelet spectrum for the decades 1970s, 1980s and 1990s. Several modes of variability for different stations have been observed: annual (1 yr), interannual (2, 2-4 and 4-8 yrs), and multi-decadal (8-16) yrs. The different scales of precipitation and runoff variability seem to be clearly related to the NAO with different degrees of correlation. Continuous wavelet coherence indicates a strong correlation between the NAO climate index and precipitation with correlations ranging from 60 to 84%, and a strong relationship between the NAO and the runoff with correlations ranging from 67 to 74% for both watersheds.

Drought is the most frequent natural disaster in Algeria during the last century, with a severity ranging over the territory and causing enormous damages to agriculture and economy, especially in the north-west region of Algeria. The above issue motivated this study, which is aimed to analyse and predict droughts using the Standardized Precipitation Index (SPI). The analysis is based on monthly rainfall data collected during the period from 1960 to 2010 in seven plains located in the north-western Algeria. While a drought forecast with 2 months lead-time is addressed using an artificial neural network (ANN) model. Based on SPI values at different time scales (3-, 6-, 9-, and 12-months), the seven plains of north-western Algeria are severely affected by drought, conversely of the eastern part of the country, wherein drought phenomena are decreased in both duration and severity. The analysis also shows that the drought frequency changes according to the time scale. Moreover, the temporal analysis, without considering the autocorrelation effect on change point and monotonic trends of SPI series, depicts a negative trend with asynchronous in change-point timing. However, this becomes less significant at 3 and 6 months’ time scales if time series are modelled using the corrected and unbiased trend-free-pre-whitening (TFPWcu) approach. As regards the ANN-based drought forecast in the seven plains with 2 months of lead time, the multi-layer perceptron networks architecture with Levenberg–Marquardt calibration algorithm provides satisfactory results with the adjusted coefficient of determination ( $$ R_{\text{adj}}^{2} $$ ) higher than 0.81 and the root-mean-square-error (RMSE) and the mean absolute error (MAE) less than 0.41 and 0.23, respectively. Therefore, the proposed ANN-based drought forecast model can be conveniently adopted to establish with 2 months ahead adequate irrigation schedules in case of water stress and for optimizing agricultural production.

The decrease in rainfall and the decrease in rainy days are also accompanied by a poor distribution of rainfall especially during the period of growth of the rain crops which usually extends from October to May. The Cheliff is under the influence of a semi-arid climate with precipitation that ranges from about 600 mm year(-1) to the northeast and 300 mm year(-1) to the west and south of the basin. The daily rainfall data used in this study concern eleven stations covering varying periods representative of different rainfall regimes in the Cheliff basin. The results obtained showed that the monthly dry sequences encountered during the rainy season decrease when the number of dry days increases, and the maximum values have been observed for the number of 1 to 7 consecutive dry days and the values were observed for a number greater than or equal to 21 consecutive dry days. It is important to say that the month of February recorded the lowest value of consecutive dry days for all stations. Also, the western stations of the study area display the largest values of the lengths of the dry sequences. Most of the stations are more correlated with the MO and AMO climatic indices than the other indices. These are the stations located west of the study area that are strongly correlated with AMO. It also appears that the total number of dry days of the stations located west of the study area is negatively correlated with SOI.

Significant changes in regional climates have been observed at the end of the twentieth century, taking place at unprecedented rates. These changes, in turn, lead to changes in global climate zones with pace and amplitude varying from one region to another. Algeria, a country characterized by climate conditions ranging from relatively wet to very dry (desert-like), has also experienced changes in its climate regions, notably in the country’s wet region, which represents about 7% of its total surface area, but is home to 75% of its population. In this study, the pace of climate zone changes as it is defined by Koppen–Geiger was analyzed for the period from 1951 to 2098 using climate data from observation and regional climate simulations over Algeria. The ability of the CORDEX-Africa regional climate models simulations to reproduce the current observed climate zones and their shifts was first assessed. Future changes over the whole of the twenty-first century were then estimated based on two Representative Concentration Pathway (RCP4.5 and RCP8.5) scenarios. Analysis of the shift rate of climate zones from 1951 to 2005 found a gradual but significant expansion of the surface area of the desert zone at an approximate rate of 650 ± 160 km2/year along with the abrupt shrinking, by approximately 30%, at a rate of 1086 ± 270 km2/year, of the warm temperate climate zone surface area. According to projections for the RCP8.5 scenario, the rate of expansion of desert climate will increase in the future (twenty-first century), particularly during the period from 2045 to 2098.

Drought and wetness events were studied in the Northeast Algeria with SPI and RDI. The study area includes a variety of climatic conditions, ranging from humid in the North, close to the Mediterranean Sea, to arid in the South, near the Sahara Desert. SPI only uses precipitation data while RDI uses a ratio between precipitation and potential evapotranspiration (PET). The latter was computed with the Thornthwaite equation, thus using temperature data only. Monthly precipitation data were obtained from 123 rainfall stations and monthly temperature data were obtained from CFSR reanalysis gridded temperature data. Both data sets cover the period 1979–80 to 2013–14. Using ordinary kriging, the gridded temperature data was interpolated to all the locations having precipitation data, thus providing to compute SPI and RDI with the same observed rainfall data for the 3-, 6- and 12-month time scales. SPI and RDI were therefore compared at station level and results and have shown that both indices revealed more sensitive to drought when applied in the semi-arid and arid zones. Differently, more wetness events were detected by RDI in the more humid locations. Comparing both indices, they show a coherent and similar behavior, however RDI shows smaller differences among climate zones and time-scales, which is an advantage relative to the SPI and is likely due to including PET in RDI.

Climate and anthropogenic changes impact on the erosion and sediment transport processes in rivers. Rainfall variability and, in many places, the increase of rainfall intensity have a direct impact on rainfall erosivity. Increasing changes in demography have led to the acceleration of land cover changes from natural areas to cultivated areas, and then from degraded areas to desertification. Such areas, under the effect of anthropogenic activities, are more sensitive to erosion, and are therefore prone to erosion. On the other hand, with an increase in the number of dams in watersheds, a great portion of sediment fluxes is trapped in the reservoirs, which do not reach the sea in the same amount nor at the same quality, and thus have consequences for coastal geomorphodynamics. The Special Issue “Modeling and Practice of Erosion and Sediment Transport under Change” is focused on a number of keywords: erosion and sediment transport, model and practice, and change. The keywords are briefly discussed with respect to the relevant literature. The papers in this Special Issue address observations and models based on laboratory and field data, allowing researchers to make use of such resources in practice under changing conditions.

Cette étude porte sur l’analyse de la variabilité spatiale et temporelle des indices de précipitation, température et débit dans le bassin versant de l’oued Mina (6 048 km2) dans le Nord-Ouest algérien pendant la période de 1979 à 2013. L’application du test non paramétrique de Kruskal-Wallis sur les indices de pluies a révélé que le total annuel des pluies et le nombre maximal de jours consécutifs pluvieux présentent une grande variabilité spatiale. Le nombre de jours de forts débits diminue du nord vers le sud du bassin. Quant au test de Mann-Kendall, il a révélé une tendance décroissante du total annuel des pluies. En revanche, les températures maximales et minimales ont significativement augmenté dans le temps. Il en est de même des séquences des jours secs consécutifs, des intensités des pluies et des jours extrêmement pluvieux. Aussi, la fréquence des jours avec des forts débits a diminué alors que celle avec des faibles débits a augmenté dans les trois oueds de Mina, Haddad et El Abd. Enfin, la baisse de pluies et l’augmentation de la température ont généré une diminution des ressources en eau., This study focuses on the analysis of the spatial and temporal variability of precipitation, temperature, and discharge indices in the wadi Mina watershed (6 048 km2) in the Algerian northwest during the period of 1979-2013.The application of the non-parametric test of Kruskal-Wallis on rainfall indices has revealed that the total annual rainfall and the maximum number of consecutive rainy days show a large spatial variability. The number of days with high discharge decreases from the north to the south of the basin. As for the Mann-Kendall test, it revealed a decreasing trend in total annual rainfall. On the other hand, the maximal and minimal temperatures significantly increased with time. It was the same for the sequences of consecutive dry days, rainfall intensities and extremely rainy days. Also, the frequency of days with high discharge has decreased, while that with low discharge has increased in the three wadis Mina, Haddad and El Abd. Finally, the decrease in rainfall and the increase in temperature have generated a decline in water resources.

Particular attention has been given in recent years to precipitation and variations in climate change scenarios by modeling these phenomena at different timescales. Regional climate models enable assessing the impact of climate change at the regional and local scales. This study aims, firstly, to analyze the rainfall variability in northern Algeria, and secondly, to evaluate future seasonal rainfall variability using regional climate models of the ENSEMBLE project. A statistical test and the bias method have been used for this study. Analysis of rainfall variability using the Pettitt test during the reference period (1961-1990) reveals a significant decrease of rainfall since the 1970s at the Tenes and Oran stations, located in the northwest of Algeria. This decrease occurs during the months of December and January (in winter), and March and April (in spring), and is associated to a reduction of 10-20 and 20-50 mm of daily rainfall, respectively, while the rainfall increases in the eastern region. Simulated data of 12 regional climate models have been compared to observations carried out during the reference period (1961-1990) using the bias method. Future seasonal rainfall variability was analyzed for two projection periods: 2021-2050 and 2070-2099. Most often, models underestimate the wet seasons and overestimate the dry seasons during the reference period. The models simulated a significant decrease of future rainfall in winter and spring over the two projected periods. Further investigations must be conducted to explain the underestimation of the models. It is also important to reconsider uncertainties that affect the results of this study.

Determining the link between rainfall and flow for a watershed is one of the most imperative problems and challenging tasks faced by hydrologists and engineers. Conceptual and Box-Jenkins hydrological models represent suitable tools for this purpose in circumstance of data Scarce and climate complexity. This research consists in a comparative study between conceptual models and Box-Jenkins model, namely, GR2M, ABCD, and the autoregressive moving average (ARIMA) which has a numerical design. The three models were applied to three catchments located in the north-west of Algeria. Basins have been selected according to the availability of long-time series of hydrological and climatic data (more than 30 years) to calibrate parsimonious models, taking into account the climatic variables and the stochastic behavior of the natural stream flow. Overall, the conceptual models perform similarly; whereas the results show that the GR2M model performed better than the ABCD in the validation stage, the stochastic model shows better results as opposed to conceptual models in the case of the Mellah Wadi which presents high permeability in its behavior. This is due to the simplicity of the model needed for data (only runoff data) and the ability of the stochastic model to produce stream flow in complex catchments. Such circumstance could be caused by different motivations. On the one hand, the diverse number of model parameters that make the ABCD the less parsimonious approach, with four parameters to be calibrated. On the other hand, the inability of the ABCD and the ARIMA model to capture and describe the groundwater processes, important for the cases study. Moreover, the validation period includes a large drought period, started in the late 1980s, which makes difficult model adaptation to different hydrological regimes.

Many studies have highlighted breaks in mean values of temperature and precipitation time series since the 1970s. Given that temperatures have continued to increase following that decade, the first question addressed in this study is whether other breaks in mean values have occurred since that time. The second question is to determine which climate indices influence temperature and rainfall in the coastal region of Northern Algeria. To address these two questions, we analyzed the temporal variability of temperature and annual and seasonal rainfall as they relate to four climate indices at seven coastal stations in Algeria during the 1972–2013 period using the Mann–Kendall, Lombard, and canonical correlation (CC) analysis methods.The annual and seasonal maximum, minimum and mean temperatures increased significantly over that time period. Most of these increases are gradual, implying a slow warming trend. In contrast, total annual and seasonal rainfall did not show any significant change. CC analysis revealed that annual and seasonal temperatures are negatively correlated with the Western Mediterranean Oscillation (WeMOI) climate index that characterizes atmospheric circulation over the Mediterranean basin. On the other hand, rainfall is positively correlated with a large-scale atmospheric index such as the Southern Oscillation Index.

The process of securing water supply is one of the biggest problems in the world. Along with the ever-increasing demand for water for different users, water resource management agencies face many challenges, some of which may be an obstacle to achieving sustainability and guaranteeing water for the various sectors of water supply. To face this dilemma, integrated water resources management is the best approach. The region of Tipaza is facing this problem. Through this work the WEAP model is applied to assess and analyze the current and projected balance of water resource management taking into account the different policies and operational factors that can affect the demand up to the year 2050. The results of the simulation showed that a deficit of 18.936Mm3 will be registered in the year 2042. For the years 2043 and 2044, the demand will be of the same order as the supply. For the period 2045 to 2050 a deficit of (3.44Mm3 to 85.48 Mm3) will be recorded in the case of scenario RCP4.5. On the other hand, in the case of the pessimistic scenario RCP8.5, the deficit will start from the year 2025 and will continue until the horizon of the year 2050 with 130.95 Mm3.

Une analyse des pluies journalieres extremes du bassin du Cheliff (plus grand bassin du Nord de l’Algerie) a ete etablie sur la periode 1971–2010. Pour cela 13 stations pluviometriques ont ete selectionnees et recueillies aupres de l’Agence Nationale des Ressources hydrauliques (ANRH). Six indices de pluies journalieres ont ete analyses pour caracteriser l’evolution temporelle de la frequence et l’intensite des pluies journalieres sur la periode d’etude. Ces indices correspondent a la pluie totale annuelle des jours de pluies ( 1 mm), aux percentiles 90, 95, 99 et 99.5% et a l’intensite journaliere des jours de pluie (1 mm). Le test de Mann–Kendall indique une tendance generale a la baisse significative pour les pluies totales et l’intensite journaliere de certaines stations. La frequence des fortes pluies ne montre pas de changement significatif de son evolution temporelle pour la majorite des stations. La recherche de relation entre les indices de pluies journalieres et les differents modes de circulation atmospherique a mis en evidence l’influence de l’oscillation mediterraneenne sur la variabilite des precipitations journalieres du Cheliff, particulierement pour les stations qui ont connu une baisse significative de leur indice de pluies journalieres

The increase in drought features in North Africa and Mediterranean regions is one of the most threatening natural hazards related to climate change. The spatial extent of this phenomenon in the North-West of Algeria has caused serious economic, social, and environmental impact with enormous losses. In this study, the return periods of drought events characterized by high severities and the three main droughts characteristics (duration, severity, and intensity) in the future under two Representative Concentration Pathway (RCP4.5 and RCP8.5) over two representative watersheds in North-West Algeria have been estimated In order to plan and manage the water resources under drought conditions.

Extreme climate events often have serious impacts on society, water resources, health and agriculture. Actually, several scientists tend to characterize these extreme phenomena by the use of extreme climatic indices. However, the analysis of teleconnection between these climate extremes indices and the indices of atmospheric oscillations is very useful for understanding the relationship and impact of these atmospheric oscillations on the occurrence and frequency of extreme climatic phenomena.

The objective of this study is to analyze the hydro-climatic regimes of the watershed of Mitidja West, and then try to evaluate the influence of climate on superficial flows. Rainfall data and databank for monthly discharges come from the National Agency of Hydraulic Resources (ANRH), rainfall are recorded from 23 rainfall stations distributed over the watershed and whose size varies from one station to another, and Time series of discharges data are generally from 1987 to 2012, but vary in duration. However, we noted that flows have been subjected to ruptures of 1975 until the middle of the 1980s. However, this reduction is due to a the climate impact associated with precipitation which decrease significantly since the end of the 75 years; or an anthropogenic impact due to the many hydraulic infrastructure development since 1985. Thus, for the simulation of the discharges from the rains, the efficiency of the model to simulate monthly discharges of the basin is given by the analysis of the criterion of Nash, of which it gave satisfactory values ​​superior to (60%), we can say, afterwards, that the GR2M model has a certain efficiency to simulate the discharges in the monthly time step and to guarantee a better understanding of the hydrological behavior of the basin.

This work aims, as a first step, to analyze rainfall variability in Northern Algeria, in particular extreme events, during the period from 1940 to 2010. Analysis of annual rainfall shows that stations in the northwest record a significant decrease in rainfall since the 1970s. Frequencies of rainy days for each percentile (5th, 10th, 25th, 50th, 75th, 90th, 95th, and 99th) and each rainfall interval class (1–5, 5–10, 10–20, 20–50, and ≥50 mm) do not show a significant change in the evolution of daily rainfall. The Tenes station is the only one to show a significant decrease in the frequency of rainy days up to the 75th percentile and for the 10–20-mm interval class. There is no significant change in the temporal evolution of extreme events in the 90th, 95th, and 99th percentiles. The relationships between rainfall variability and general atmospheric circulation indices for interannual and extreme event variability are moderately influenced by the El Nino-Southern Oscillation and Mediterranean Oscillation. Significant correlations are observed between the Southern Oscillation Index and annual rainfall in the northwestern part of the study area, which is likely linked with the decrease in rainfall in this region. Seasonal rainfall in Northern Algeria is affected by the Mediterranean Oscillation and North Atlantic Oscillation in the west. The ENSEMBLES regional climate models (RCMs) are assessed using the bias method to test their ability to reproduce rainfall variability at different time scales. The Centre National de Recherches Meteorologiques (CNRM), Czech Hydrometeorological Institute (CHMI), Eidgenossische Technische Hochschule Zurich (ETHZ), and Forschungszentrum Geesthacht (GKSS) models yield the least biased results.

The exposure of the Earth’s surface to the energetic input of rainfall is one of the key factors controlling water erosion. While water erosion is identified as the most serious cause of soil degradation globally, global patterns of rainfall erosivity remain poorly quantified and estimates have large uncertainties. This hampers the implementation of effective soil degradation mitigation and restoration strategies. Quantifying rainfall erosivity is challenging as it requires high temporal resolution(−1 h−1 yr−1, with the highest values in South America and the Caribbean countries, Central east Africa and South east Asia. The lowest values are mainly found in Canada, the Russian Federation, Northern Europe, Northern Africa and the Middle East. The tropical climate zone has the highest mean rainfall erosivity followed by the temperate whereas the lowest mean was estimated in the cold climate zone.

In this paper, we study the impact of climate change on river regimes in several parts of Africa, and we look at the most probable causes of these changes either climatically or anthropogenically driven. We study time series of updated monthly and annual runoff of rivers of North Africa, West Africa (Sahelian and humid tropical regions) and Central Africa, including the largest river basins: Niger and Volta rivers in West Africa, and Congo and Ogooue rivers in Central Africa. The recent years are studied in the perspective of multi-decadal variability. In West Africa and in a part of Central Africa, the climate has changed since 1970, and rainfall has not returned to previous annual amounts, except in Equatorial Africa. The consequences of the long-lasting drought are, depending on the area concerned, the modification of seasonal regimes (Equatorial area), the groundwater table decrease (Tropical humid area) and the land cover degradation (Sahelian area). The increasing number of dams and of agricultural areas also plays a major role on the modification of river regimes. The population increase will continue to impact on the environment: land cover change, deforestation, agriculture and increasing number of dams will be associated with a reduction of water and sediment discharges to the sea, and major impacts on downstream ecosystems and coastal areas. It seems necessary to share with stakeholders a comprehensive approach of the water cycle from the basin to the sea, to prevent long-lasting damages to ecosystems and infrastructures. Copyright © 2013 John Wiley & Sons, Ltd.

Algeria is periodically affected by severe and repeated flooding. Flood hazard studies require the estimation of extreme flood flows. To predict and estimate the characteristics of maximum flows, knowledge of their distribution law is essential. The L-moments method was used to determine homogeneous regions and the appropriate distribution for these regions. Three homogeneous regions were delineated. This technique produced a Pearson type III distribution for the coastal region and the Tell Atlas and a Pareto distribution for the steppe regions and high plateaus of Eastern and Western Algeria. To estimate maximum flow at ungauged sites for different return periods, the 'index-flood' method was used. An empirical formula was developed that uses the average annual maximum flow as a function of catchment area and the average slope of the main channel to estimate maximum flow at any point on the Oued. The coefficient of determination and the Nash criterion, for the three regions, are superiors to 88% and 83% respectively. The root mean squared error, for the three regions, is less than 12%. These values show the robustness of the developed models.

Study region: North Algeria. Study focus: The semi-arid to arid Chéliff–Zahrez basin faced several droughts with severe impacts on agriculture due to the high temporal and spatial distribution of rainfall. We explored the potential of the Standardized Precipitation Index (SPI), Markov chain models, the Drought Index and time series modelling to characterize meteorological drought. Time series of annual precipitation (1960–2010) from 65 meteorological stations across the basin were used. The basin was subdivided into five subbasins to account for spatial variability. New hydrological insights for the regions: The analysis of the Standardized Precipitation Index showed few droughts in the period 1960–1970, whereas in the 1990s a multi-year drought occurred with SPIs as low as −2 (extremely dry) in many subbasins. The Markov chain analysis learnt that the probability of having two consecutive drought years appears to be higher in the southern subbasins. The Drought Index derived from transition probabilities indicates that the southern and the southwestern parts of the Chéliff–Zahrez basin are most drought prone. Time series modelling was applied to compute the SPI for different return periods (6‐17 years). Eleven models were tested and it appeared that the Asymmetric Power Autoregressive Conditional Heteroskedasticity (APARCH) approach was best performing based on several information criteria. For a return period of 17 years, the SPI is lower than −1.5 (severely dry) in many subbasins. Keywords: Meteorological drought, SPI, Markov chain, Time series modelling, Drought maps, Chéliff–Zahrez basin

In the Mediterranean the environment is under pressure from agricultural and urban development, changes in agricultural practices and international markets, and climate change. Moreover, many studies show a steady increase in the agro-pastoral pressure and land degradation and their impacts on water resources and soil, and ultimately the lives of local people. But few studies address these issues across the inclusive scale of large river basins. The conference held at Tipaza in Algeria, from which come several papers published in the Journal of Water Science in 2013, was intended to reflect on the topics, methods and tools available to study the relationships among humans, the environment and sediment transport at this large scale, with the result expected to improve the potential for dialogue between researchers and developers who make decisions for regional macro surfaces. The topics discussed at the conference that appear in the articles published here concern the factors responsible for the variability of sediment transport: climate change and anthropogenic changes, such as agricultural activity and water projects; relationships between land-cover/land-use, rainfall-runoff processes and sediment transport; modeling of sediment transport; and the interest of a multi-scale approach, predominantly a spatial one, for addressing the geographical realities of large basins and scale transfer issues, particularly in Mediterranean and semi-arid areas., En Méditerranée l’environnement est soumis aux pressions du développement agricole et urbain, aux changements dans les pratiques agricoles et les marchés internationaux, et au changement climatique. Par ailleurs, de nombreux travaux témoignent d’une augmentation croissante de la pression agro-pastorale et de la dégradation des sols et de leurs conséquences sur les ressources en eau et en sol, et in fine sur les conditions de vie des populations locales. Mais peu de travaux abordent ces questions à l’échelle intégratrice des grands bassins versants. La conférence de Tipaza en Algérie, dont sont tirés plusieurs articles parus dans la Revue des Sciences de l’Eau en 2013, avait pour objectif de mener une réflexion sur les problématiques, méthodes et outils disponibles pour étudier les relations homme, environnement et transports solides à cette échelle, avec comme issue attendue d’améliorer le potentiel de dialogue entre les chercheurs et les développeurs qui ont à prendre des décisions pour des surfaces macro régionales. Les thèmes traités lors de cette conférence et qui apparaissent dans les articles publiés ici concernent les facteurs à l’origine de la variabilité des transports solides : changement climatique, changements anthropiques – tels que les activités agricoles et aménagements hydrauliques; les liens entre l’occupation du sol, les processus pluie-débit et le transport sédimentaire; la modélisation des transports sédimentaires; et l’utilité d’une approche multi-échelle, principalement spatiale, pour appréhender les réalités géographiques de grands bassins et la question du transfert d’échelle, en particulier dans les régions méditerranéennes et semi-arides.