This study investigates teleconnections between rainfall in the Ogooué River Basin (ORB) and sea surface temperature (SST) in the tropical ocean basins. The Maximum Covariance Analysis (MCA) is used to determine coupled patterns of SST in the tropical oceans and rainfall in the ORB, depicting regions and modes of SST dynamics that influence rainfall in the ORB. The application of MCA to rainfall and SST fields results in three coupled patterns with squared covariance fractions of 84.5%, 76.5%, and 77.5% for the Atlantic, Pacific, and Indian tropical basins, respectively. Computation of the correlations of the Savitzky–Golay-filtered resulting expansion coefficients reached 0.65, 0.5 and 0.72, respectively. The SST variation modes identified in this study can be related to the Atlantic Meridional Mode for the tropical Atlantic and the El Niño Southern Oscillation for the tropical Pacific. Over the Indian Ocean, it is a homogeneous mode over the entire basin, instead of the popular dipole mode. Then, the time-dependent correlation method is used to remove any ambiguity on the relationships established from the MCA.

In the context of climate change, the increasing frequency and intensity of extreme events are disrupting dam management in West Africa. Few studies have examined their impacts on water inflows and the operational management of dams. The Kossou Dam, located at the outlet of the White Bandama watershed in central C & ocirc;te d'Ivoire offer a relevant case for such analysis. This study assesses the effect of extreme weather events on the river flows and dam operations using meteorological data (rainfall and temperatures) from nine (9) weather stations, combined with hydrological (Inflows) and operational record (outflows, storage, water levels, and energy). The methodology combines probability analysis, extreme climate indices and statistical tests, including the Mann - Kendall trend test (and Sneyers' modification) and correlation analyses. Results show spatial variability in extremes rainfall and temperature in the White Bandama watershed. Trends in extreme rainfall are generally not significant at the 95% confidence level, while extreme temperature indices vary by stations. Correlations above 0.30 between rainfall extremes and flows confirm rainfall's influence on flow rates whereas extreme temperature indices show no significant link with flows. For operational parameters, only water level and storage correlate (below 0.40) with Tmax, CSDI and WSDI.

Groundwater resources are currently important for supplying populations, agriculture, and industry. However, the balance of these resources is threatened by intense anthropogenic pressure and climate change. In this context, hydrogeological modeling becomes one of the best alternatives for designing appropriate management plans. This work aims to model the hydrogeological behavior of the eastern part of the Annaba plain (Northeastern Algeria) and assess the future availability of groundwater in this region. To achieve this, several datasets (hydrodynamic properties, recharge, piezometric levels, outputs from Regional Climate Models, etc.) were used in the MODFLOW model (via the Groundwater Modeling System interface). The behavior of the studied aquifer was satisfactorily simulated in both steady-state (mean residual = -0.2 m) and transient (Nash ≥ 0.53) conditions. The REMO model, which appears to provide the most reliable forecasts, predicts a decline of no more than − 27.4

To anticipate disasters (drought, floods, etc.) caused by environmental forcings and reduce their impacts on its fragile economy, sub-Saharan Africa needs a good knowledge of the availability of current water resources and reliable hydroclimatic forecasts. The objective of this study is to evaluate the availability of current water resources and their future evolution in a forest watershed undergoing accelerated urbanization (Mefou), but also to separate the respective impact of land use and land cover change (LULCC) and climate variability (CV) on the evolution of this resource. For this, the SWAT (Soil and Water Assessment Tool) model was used. The performance of this model is satisfactory in calibration and validation, with R2 and NSE greater than 0.64. Biases lower than − 7.9

The objective of this study is to investigate the effects of rainfall variability and anthropogenic changes on river discharge in the Benoue and the Logone river basins over the last 7 decades (1950-2018). To achieve this goal, hydrometeorological data from these basins were analyzed using the Pettitt and Mann-Kendall tests. Our results show that negative rupture was observed in the hydrometeorological time series of these basins at the annual time step in 1970-1971. The deficits associated with this rupture are estimated at -7% for rainfall and -28% for river flows. The wet season shows similar developments. However, from the 1990s onward, there has been a significant increase in the mean annual flows of the Benoue River, which coincides with that of the rainfall during the same decade. This increase over the recent decades could also be expected in response to an increase in impervious surface area in the catchment area, which could compensate for the deficit generated by the post-1990s rainfall deficit through an increase in runoff. Since the filling of the Lagdo Dam in 1983, an increase in all ranges of minimum flow, as well as an increase in the variability of extreme flows, has been detected.

Climate change is increasing the intensity and frequency of natural disasters. Marine submersion and flooding appear to be major consequences of this forcing, and the damage they cause is regular and significant (e.g., the spread of diseases and destruction of infrastructure). In tackling these disasters, it is useful to start with a vulnerability assessment. The objective of this study is to assess the vulnerability of populations to marine submersion (Manoka and Cape Cameroon) and flooding (Sodiko) in the Wouri estuary. Collecting the data to achieve this objective necessitated several approaches, ranging from surveys of residents and managers to the collection of topographical data, water levels, and participatory mapping. For Sodiko, the submersible zone (< 2.23 m) delimited from the Digital Elevation Model (DEM) generated included 117 ha (65

ABSTRACT This article aims to produce a groundwater potential zone (GWPZ) map of the Nyong basin using an integrated analytical hierarchy process driven in a geographic information system (GIS) environment. For this, seven parameters (rainfall, geology, slopes, drainage density, land use and land cover, lineament density, and soil) known to influence the availability of groundwater were considered. The results obtained show that the Eastern part of the basin holds the largest quantities of groundwater. The produced map shows that this region includes high and very high GWPZs (yield > 6 l/s). It is essentially characterized by abundant rainfall (on average 135–136 and 131–134 mm), low slopes, significant drainage and lineament densities, and significant forest cover. On the other hand, the opposite region (west), which includes the low and very low GWPZs, is characterized by less abundant precipitation (on average 121–125 and 125–128 mm), significant slopes, lower drainage and lineament densities, and greater impervious areas. With a success rate of 80%, confidence deserves to be placed in the GWPZs map produced. It can be considered in water supply projects in this basin. Such work has never been done in this basin before.

Flooding constitutes a major problem for the inhabitants of Douala City in general and those of the Tongo Bassa watershed (TBW) in particular. Faced with this situation, public authorities need to put in place measures to mitigate the vulnerability of populations to these disasters. This article aims to map flooding risk areas in the TBW using the geographic information system, field data (historical flood points), remote sensing data (Sentinel II image) and the frequency ratio model. The map produced shows that 1.41, 8.88, 28.51, 33.86 and 27.33% of the basin area are respectively delimited into very low, low, medium, high and very high flood vulnerability classes. High and very high flooding risk areas (those where flooding is most likely to occur) occupy more than half of the basin (61.19%). These areas are characterized by significant imperviousness, low altitudes, weak slopes, significant proximity to watercourses and clayey soils. Most of the houses in the basin (66.92%) are located in areas affected by these two levels of exposure (high and very high). With respective success and prediction accuracy rates of 89 and 96.78%, a certain confidence deserves to be placed on the map of flooding risk areas produced.

Study regionMbakaou and Bamendjing basins (Sanaga River sub-basins).Study focusIn this study, the availability of water resources was assessed over the period 2002–2019, based on the SWAT (Soil and Water Assessment Tool) hydrological model and certain meteorological and spatial reference data available for the region (Merra2, Landsat, etc.). Forecasts of its evolution were then made with the same tool (SWAT) over two futures periods (near 2024–2035 and medium: 2036–205) based on data from four (04) regional climate models (RCMs) (CCCma, HIRHAM5, RCA4 and REMO) and future land use and land cover (LULC) data simulated using the CA-Markov procedure. To separate the impact of climate variability (CV) and land use and use and land cover changes (LULCCs) on future water resources, two evolution scenarios (experiments) were established: (1) the impact of the CV, by associating future climate data with LULC from the historical period; (2) the impact of LULCCs, by combining future LULC maps with climate data from the historical period.New hydrological insights for the regionThe performances of the SWAT model are satisfactory in calibration and validation on the two basins with R2, NSE and KGE greater than 0.68. Two models (CCCma and REMO) predict a decline in water resources in these basins, and two others (HIRHAM5 and RCA4) the opposite. The REMO model seems the most reliable. It predicts a drop in precipitation and runoff (SURQ) in the two basins that do not respectively exceed –19% and –31%. CV is the only forcing whose impact will be visible in the dynamics of future water resources, given the insignificant changes expected in the evolution of LULC patterns. The results of this study could contribute to improving the management of water resources in the studied basins and the region.

To anticipate disasters (drought, floods, etc.) caused by environmental forcing and reduce their impacts on its fragile economy, sub-Saharan Africa needs a good knowledge of the availability of current water resources and reliable hydroclimatic forecasts. This study has an objective to quantify the availability of water resources in the Nyong basin and predict its future evolution (2024–2050). For this, the SWAT (Soil and Water Assessment Tool) model was used. The performance of this model is satisfactory in calibration (2001–2005) and validation (2006–2010), with R2, NSE, and KGE greater than 0.64. Biases of − 11.8

Land surface temperature (LST) estimation at the river sub-basin level is crucial for developing land use planning at the basin scale and beyond. The main goal of this study was to analyze LST variations in response to land use mode (LUM) changes in the Mefou River sub-basin (Southern Cameroon) using geospatial techniques. To achieve this goal, we used Landsat 7 Enhanced Thematic Mapper Plus (2000 and 2010) and Landsat 8 Operational Land Imager (OLI)/Thermal Infrared Sensor (TIRS) data for 2020. We also used air surface temperature data from the Climatic Research Unit (CRU) to validate the LST. Our results reveal that between 2000 and 2020, the Mefou watershed recorded significant changes in LUMs, which were mainly manifested by an increase in impervious areas (IAs) (buildings and roads (+10%); bare soils and farmlands (+204.9%)) and forest reduction (−31.2). This decrease in the forest was also reflected by a reduction in NDVI values, the maximum of which went from 0.47 in 2000 to 0.39 in 2020. Contrary to the forest area and the NDVI values, the LSTs of the investigated basin increased over the period studied. There is a strong negative correlation between LST and NDVI. In general, high LSTs correspond to low NDVI values. For the years 2000, 2010 and 2020, the links between these two variables are materialized by respective correlation coefficients of −0.66, −0.74 and −0.85. This study could contribute to understanding the impact of LUM changes on the local climate, and could further provide assistance to policymakers in regard to land use planning and climate change mitigation strategies.

Le changement climatique et l’anthropisation sont les principaux forçages qui influencent significativement la variabilité des écoulements des cours d’eau. Cependant, la compréhension de leur impact simultané sur les écoulements reste limitée. L’objectif de cette étude est d’appréhender l’impact de la variabilité des précipitations et de l’anthropisation sur les écoulements du bassin versant de la Mefou sur une période récente (1950-51 à 2018-2019). Pour cela, les données hydropluviométriques du bassin concerné ont été analysées au moyen du test de Pettitt. De même, la dynamique des principaux MOS (modes d’occupation du sol) a pu être appréciée, et ce au moyen des classifications supervisées effectuées à partir du traitement des images satellitaires Landsat du bassin étudié à deux dates. Les résultats de cette étude montrent que les débits moyens (+27,8% à +66,4%) et extrêmes (31,2% à 82,3%) de ce bassin augmentent depuis 1985-86, contrairement à la pluviométrie, qui elle diminue d’une façon générale pour toutes les saisons à compter de la décennie 1970, en dehors de l’été (+42,8%), où l’inverse est observé. Les changements d’occupation du sol (augmentation des espaces imperméabilisés et diminutions de la forêt et des plans d’eau) semblent être la cause principale de la hausse des écoulements relevée. Les évolutions pluviométriques observées dans ce bassin ont juste contribué à amplifier la variabilité des écoulements durant la période étudiée. L’été et le printemps pour lesquels les pluies ont respectivement enregistré une rupture à la hausse et une absence de rupture sont également les saisons pour lesquelles les augmentations des écoulements sont les plus importantes. A l’inverse, l’automne et l’hiver qui ont enregistré des diminutions significatives des pluies ont connu les augmentations les moins importantes. Ces résultats pourraient être utiles pour la planification à long terme de la demande et de l'utilisation de l'eau dans ce bassin, ainsi qu'à l’amélioration des simulations futures du débit du collecteur principal et la prévention des catastrophes socio-environnementales comme les inondations. The objective of this study is to understand the impact of rainfall variability and anthropization on the flows of the Mefou watershed over a recent period. For this, the hydropluviometric data of the catchment concerned were analyzed using the Pettitt test. Likewise, the dynamics of the main land-use patterns could be assessed, using supervised classifications carried out from the processing of Landsat satellite images of the basin studied at two dates. The results of this study show that the average and extreme flows of this basin have been increased since 1985-86, unlike the rainfall, which generally decreases for all seasons from the 1970s, apart from the summer, where the reverse is observed. Land-use changes (increase in impervious areas and a decrease in forest and water bodies) seem to be the main cause of the observed increase in runoff. The rainfall changes observed in this basin have just contributed to amplifying this increase in runoff in some cases and attenuating it in others. The summer and the spring for which the rainfall recorded respectively an increasing break and no break are also the seasons for which the increases in runoff are the most important. Conversely, autumn and winter, which saw significant decreases in rainfall, experienced the smallest increases. These results could be useful for long-term planning of water demand and use in this basin, as well as for improving future simulations of main collector flow and preventing socio-environmental disasters like flooding.

Study region: Lobo River Catchment (Cote d'Ivoire) Study focus: In this study, four regional climate models (RCMs) (RC4; CCLM4-8-17; RACMO22T and REMO) for the 2030 and 2050 periods compared to the reference period (1986-2005), combined with a simulation of land use and land cover (LULC) with Land Change Modeler, are used to drive the CEQUEAU model to quantify their impact on inflows to the Lobo River reservoir. 1988-2006 is used as a calibration period, whereas 2007-2015 is used for the validation. Three scenarios were used. First, varying LULC and keeping climate parameters static over the baseline period (scenario 1); in scenario 2, varying RCMs and keeping LULC static over the baseline period and in scenario 3, simultaneous variation of LULC and RCMs. New hydrological insights for the region: CEQUEAU showed good performance during calibration and validation: NSE (0.7, 0.75); R2 (0.83, 0.65); PBIAS (14.1%, 12%) and RMSE (0.83, 2.15). The results show that a decrease in precipitation by 2030 (-14.6%), by 2050 (-15.2%) under sce-nario 2 (RCP 4.5 and 8.5) and by -6.1% under RCP 4. 5 (Scenario 3), we observe an increase in runoff of 10.8-18.87% (Scenario 1), 1.2-4.46% (RCP4.5), 3.35% and 2.7% (RCP8.5) (Scenario 2) and 6.58-11.83 (RCP 4.5), 14.83-17.72% (RCP 8.5) (scenario 3). Changes in LULC were iden-tified as the main causes, rather than climate variability.

Due to climate and environmental changes, sub-Saharan Africa (SSA) has experienced several drought and flood events in recent decades with serious consequences on the economy of the sub-region. In this context, the region needs to enhance its capacity in water resources management, based on both good knowledge of contemporary variations in river flows and reliable forecasts. The objective of this article was to study the evolution of current and future flows in the Nyong River Basin (NRB) in Cameroon. To achieve this, the Pettitt and modified Mann–Kendall tests were used to analyze the hydrometeorological time series in the basin. The SWAT model was used to simulate the future flows in the NRB. During the 1970s, the Nyong basin experienced a joint decrease in rainfall and flow. Despite a general decrease in future precipitation, a significant increase in runoff is expected in this basin, regardless of the period (2022–2060 or 2061–2100), the model (RCA4 or CCCma) and the scenario (representative concentration pathway (RCP) 4.5 or RCP8.5). This increase in flow will be the result of the increase in impervious areas to the detriment of forest in the basin, which will compensate for the drop in precipitation with an increase in runoff.

Climate change, variability and anthropogenic forcings such as land use change are the main forcings of river discharge variability. However, an understanding of their simultaneous impacts on river discharge remains limited in some parts of the world. To shed light on this issue, the objective of this article is to investigate the effects of rainfall variability and land use change on river discharge in the Nyong basin (at Olama and Mbalmayo gauging stations) and some of its sub-basins (So’o and Mefou) over the long period 1950–2018. To achieve this goal, hydro-meteorological data of the Nyong basin and sub-basins were analyzed using the Pettitt test. Likewise, land use changes in the basin and sub-basins were also analyzed using supervised classifications of Landsat satellite images of the basins at different periods (1973, 2000 and 2018). On the annual scale, rainfall has decreased statistically over the studied basins. In the large basins (Olama and Mbalmayo), this decrease in rainfall is synchronous with that of discharges, while it is concomitant with an increase in the Mefou (small basin). After the ruptures within time series identified in the annual modules, the extreme discharges (maximum and minimum) decreased in Olama; in Mbalmayo, the maximum discharges remained stable while the minimum discharges decreased. On the other hand, the maximum and minimum discharges have significantly increased in the Mefou. The stability of maximum discharges at Mbalmayo and the increase in extremes on the Mefou in a context where the precipitation that generates the discharge has decreased can be attributed to land use change. These changes are essentially marked by an increase in impervious areas and a reduction in forest cover. On the seasonal scale, the impact of precipitation in the dry season is visible on the flows of the rainy seasons that follow them on the large basins (Olama and Mbalmayo). Between the decades 1970–1990 and 2000–2010, there was respectively a significant increase, then a decrease in summer precipitation, which impacted the autumn discharges in the same direction. Conversely, between the same intervals, there was a significant decrease, then a slight increase in winter precipitation. The impact of winter precipitation on the spring discharge is more visible during the first period only (1970–1990). During the second period, winter precipitation seems to have more of an impact on the runoff for the same season. In the Mefou sub-basin, the precipitation plays an essentially amplifying role in the increase in discharge in the seasons during which they occur. Those having experienced an increase, or a maintenance of precipitation (summer and spring) recorded the most significant increases in discharges. These results could be useful for long-term planning on the demand and use of water, as well as flood management in the basins

This article has as objectives to investigate the impact of precipitation variability and land use change on the hydrological dynamics of the Mefou river over the recent period (1963-2018), and draw up a basin flooding risk areas map. To achieve these goals, hydrometeorological data of this basin were analyzed using the Pettitt and Mann Kendall tests. Likewise, flooding risk areas was produced from Frequency Ratio (FR) model. Average and extreme flows of Mefou river have increased since 1985-86, unlike the rainfall, which generally decreased for all seasons from the 1970s, apart from summer, where the reverse was observed. Changes in land use (increase impervious areas (+530%) and a decrease in forest (-52.9%) and water bodies (-80.4%)) seem to be the main cause of the increase in flows observed. Floods are often recurrent in basins with such hydrological behaviour. To enable policymakers to reduce the vulnerability of populations to this disaster, the proposed flood map shows that 2.67, 7.22, 22.5, 35.25 and 32.36% of the catchment area are respectively delineated into very low, low, medium, high and very high flood vulnerability classes. These results could be useful for the management of water resources and associated hydrological risks in the basin investigated.

Abstract This article has as objective to investigate the impact of rainfall variability and land use changes on river discharge in the Mefou basin over the recent period (1963–2018). To achieve this goal, hydrometeorological data of this basin were analyzed using the Pettitt test. Likewise, land use changes were also analyzed using supervised classifications of Landsat satellite images at two periods (1973 and 2018). Average and extreme flows of Mefou river have increased since 1985-86, unlike the rainfall, which generally decreased for all seasons from the 1970s, apart from summer, where the reverse was observed. Changes in land use (increase impervious areas and a decrease in forest and water bodies) seem to be the main cause of the increase in runoff observed. The rainfall plays an essentially amplifying role in the increase in discharge in the seasons during which they occur. Those having experienced an increase or a maintenance of rainfall (summer and spring) recorded the most significant increases in discharges. These results could be useful for the improvement of future simulations of the Mefou river flow and the prevention of socio-environmental disasters like floods in the basin.

The objective of this study is to understand the impact of rainfall variability and anthropization on the flows of the Mefou watershed over a recent period. For this, the hydropluviometric data of the catchment concerned were analyzed using the Pettitt test. Likewise, the dynamics of the main land-use patterns have been assessed, using supervised classifications carried out from the processing of Landsat satellite images of the basin studied at two dates. The results of this study show that the average and extreme flows of this basin have been increased since 1985-86, unlike the rainfall, which generally decreases for all seasons from the 1970s, apart from the summer, where the reverse is observed. Land-use changes (increase in impervious areas and a decrease in forest and water bodies) seem to be the main cause of the observed increase in runoff. The rainfall changes observed in this basin have just contributed to amplifying this increase in runoff in some cases and attenuating it in others. The summer and the spring for which the rainfall recorded respectively an increasing break and no break are also the seasons for which the increases in runoff are the most important. Conversely, autumn and winter, which saw significant decreases in rainfall, experienced the smallest increases. These results could be useful for long-term planning of water demand and use in this basin, as well as for improving future simulations of main collector flow and preventing socio-environmental disasters like flooding. Keywords: Mefou, variability, precipitation, runoff, land use patterns

Abstract Climate change and variability and anthropogenic forcings such as land use change are the main forcings of river discharge variability and hydrological risks. However, these issues are very less addressed in central Africa. This article aims to investigate the impact of precipitation variability and land use change on the hydrological dynamics of the Mefou river over the recent period (1963–2018) and draw up a basin flooding risk areas map. To achieve these goals, hydrometeorological data of this basin were analyzed using the Pettitt and Mann Kendall tests. Likewise, flooding risk areas was produced from the Frequency Ratio (FR) model. Average and extreme flows of the Mefou river have increased since 1985-86, unlike the rainfall, which generally decreased for all seasons from the 1970s, apart from summer, where the reverse was observed. Changes in land use (an increase in impervious areas (+ 530%) and a decrease in forest (-52.9%) and water bodies(-80.4%)) seem to be the leading cause of the increase in flows observed. Floods are often recurrent in basins with such hydrological behaviour. To enable policymakers to reduce the vulnerability of populations to this disaster, the proposed flood map shows that 2.67%, 7.22%, 22.5%, 35.25% and 32.36% of the catchment area are respectively delineated into very low, low, medium, high and very high flood vulnerability classes. These results could be useful for the management of water resources and associated hydrological risks in the basin investigated.