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.

Despite the importance of inland waters of African Equatorial Belt (humid tropics) in carbon (C) and greenhouse gas control, geochemical transfer of C, major and trace elements in fluvial systems of this region remains poorly investigated. Towards filling this gap, this study investigates the Ogooue River Basin (ORB), a major tropical river system in Gabon (Western Central Africa, WCA), focusing on the dissolved and colloidal transport, fractionation, and mobility of organic carbon, major, and trace elements. Water samples were collected using a twophase approach. First, snapshot sampling was conducted during two cruise campaigns in the wetland-dominated Lower Ogooue Ramsar Zone during rainy seasons in 2022 and 2023, targeting several main river locations and its major tributaries, together with lakes and organic-rich hotspots of stagnant waters, including submerged shorelines and ancient raised fields. A time-series sampling was also carried out with 11 samples from the main stem at Lambarene (Lower Ogooue) and 24 fortnightly samples from Franceville (upper reaches) over a year. Analyses included major and trace elements, dissolved organic and inorganic carbon in <0.22 mu m filtrates, and stepwise size fractionation using 3.1 mu m and 0.22 mu m filters, together with dialysis through 25 kDa and 1 kDa membranes. The Ogooue River exhibits high elemental yield (watershed area - normalized export) compared to other organic-rich fluvial systems, with aluminum 37 times, iron 3 times, and dissolved organic carbon (DOC) 4 times higher than those of boreal and sub-Arctic rivers. DOC specific fluxes are also 2.8 times higher than the Congo River and comparable to the blackwater Nyong River. Colloidal transport of solutes dominates the overall export, with organic carbon primarily carried in high molecular weight (HMW) colloids and trace elements such as Fe and Al associated with coarser colloidal fractions. Seasonal flooding and short-term discharge variations strongly influence annual transport, as demonstrated during the high-discharge period of 2022-2023, when DOC concentrations ranged from 5 to 15 mg/L and DOC yields reached 9.3 tC/km2/year. These increases are attributed to the mobilization of organic-rich matter from submerged wetlands and riparian zones. The Ogooue's colloidal behavior aligns with boreal systems for elements like Fe and Al but differs in the transport of alkaline and alkaline earth elements, reflecting unique biogeochemical traits among tropical rivers. Its significant contribution to regional and global carbon and trace element cycles underscores its critical ecological and geochemical importance. This study highlights the need for high resolution hydrometeorological monitoring to better understand the Ogooue's elemental transport dynamics and sensitivity to environmental changes.

Floods represent the most prevalent natural disaster globally, inflicting significant physical and economic harm on coastal megacities such as Douala. The objective of the current work is to provide key insights into the spatial dynamics of water levels and, consequently, impacts on flood-prone areas, which are critical for the implementation of early warning systems and other effective interventions to mitigate flood risks in the city of Douala. Field measurements from the flood event on August 21, 2020, were utilized to analyse the hydrological changes in the Wouri-Nkam River Estuary. The findings revealed two distinct dynamics: the lower segment (Douala harbour) displays a semi-diurnal tidal signal characterized by a constant flood-ebb oscillation, while the upper riverine section (Bona’Anja siga Bonjo hamlet) demonstrates an eroding semi-diurnal nature. The flood severity index (FSI) indicated the highest values in the upper riverine section. The maximum FSI value was recorded near Bonagang (FSI = 3.50), followed by Bona’Anja (FSI = 2.087). In contrast, the minimum value (FSI = 1) was observed at the Douala port (estuarine end). The estuarine side exhibited minimal tidal attenuation rates, ranging from 9 to 13

Located in southern Cameroon, at the bottom of the Gulf of Guinea, the Kribi coast has contributed over the years to the country's economic development (seaside tourism, mining and oil exploitation, etc.). In recent decades, the coastline has been subject to a number of stresses, such as coastal erosion. However, virtually no work has been done in this area to assess the degree of vulnerability of this coastline to erosion. The objective of this article was to assess the physical and socio-economic vulnerability of a 31.5-km stretch of the Kribi coastline using geographic information systems (GIS). The results obtained have made it possible to map the vulnerable areas on this coast. More than two-thirds (68.3%) of the Kribi coastline are highly physically vulnerable to erosion risks, consisting mainly of sandy accumulations and creeks, while nearly one-third (31.7%) of the coastline has low to moderately vulnerability, consisting of rocky promontories and rocky shores. On the other hand, more than half (58.7%) of the coastline is highly vulnerable to erosion from a socio-economic perspective, consisting mainly of densely populated urban areas with well-developed road networks and a rich heritage. More than a third (41.3%) of the coastline has low to moderate socio-economic vulnerability, consisting of areas that are difficult to access and almost unexploited. The results of this study can be used as a decision-making tool to anticipate critical areas and guide development policies for sustainable coastal management, given that an industrial and port complex is gradually being built around the deep-water port of Kribi. It also contributes to enriching the assessment techniques used to date.

The Sanaga is Cameroon’s most important river, supplying almost 90

Promoting renewable energy sources, particularly in the solar industry, has the potential to address the energy shortfall in Central Africa. Nevertheless, a difficulty occurs due to the erratic characteristics of solar irradiance data, which is influenced by climatic fluctuations and challenging to regulate. The current investigation focuses on predicting solar irradiance on an inclined surface, taking into consideration the impact of climatic variables such as temperature, wind speed, humidity, and air pressure. The used methodology for this objective is Artificial Neural Network (ANN), and the inquiry is carried out in the metropolitan region of Douala. The data collection device used in this research is the meteorological station located at the IUT of Douala. This station was built as a component of the Douala sustainable city effort, in partnership with the CUD and the IRD. Data was collected at 30-min intervals for a duration of around 2 years, namely from January 17, 2019, to October 30, 2020. The aforementioned data has been saved in a database that underwent pre-processing in Excel and later employed MATLAB for the creation of the artificial neural network model. 80% of the available data was utilized for training the network, 15% was allotted for validation, and the remaining 5% was used for testing. Different combinations of input data were evaluated to ascertain their individual degrees of accuracy. The logistic Sigmoid function, with 50 hidden layer neurons, yielded a correlation coefficient of 98.883% between the observed and estimated sun irradiation. This function is suggested for evaluating the intensities of solar radiation at the place being researched and at other sites that have similar climatic conditions.

Mangrove ecosystems provide key ecosystem services in coastal areas. This study describes the riparian mangrove of the Wouri estuary, in the Douala region (Cameroon), emphasizing the changes in this ecosystem over the past decade and its current state. It highlights the different groups of actors who participate in the management and regulation of the resource. Finally, an analysis of the governance of the mangrove wood resource based on the theory of common goods by Elinor Ostrom (1990) is proposed by examining the results obtained from the previous points. The scientific interest lies in contributing to a better understanding of the socio-ecological changes in the mangrove in the context of increasing anthropogenic pressures, highlighting the governance challenges and conservation opportunities in a strategic region of Central Africa. This research reveals complex processes that characterize mangrove ecosystems on the Manoka and Cap Cameroon Islands. The lack of urbanization regulations, continued infrastructure growth, repeated flooding, and coastal erosion all have a negative impact on natural landscapes and forests. The use of wood for smoking and fishing, as well as coastal pollution resulting from deficient garbage management, also have a considerable influence. Strategic interventions are needed to ensure sustainable ecosystem management. Recommendations include the application of rules to prevent forest overexploitation.

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

Low-lying coastal regions are generally vulnerable to climate change, and particularly to sea level variations. Understanding how these variations affect the coastal population requires an access to sea level measurements. Good quality in-situ sea level data are seldom available, with most long, research quality data in Europe and North America. In contrast, satellite altimetry provides more than three decades of near-global, continuous and freely available sea level measurements. Thanks to recent advances in processing and instruments, these observations have now become reliable to a few kilometers from the coast. In this study, using the available in-situ tide gauge data as a reference, we explore the ability of the recent X-TRACK/ALES high-resolution coastal altimeter product to derive the ocean tide and the long-term sea level changes along the West African coast. This region was chosen because it is under-sampled in terms of in-situ observations and would benefit greatly from the availability of freely accessible satellite data sets. To select the altimetry observations closest to the coast, we first define virtual tide gauges as close as possible to the intersection between each satellite track and the land. Sea level anomalies derived from the virtual stations were observed to be similar to those from the corresponding tide gauge stations: correlation values are between 0.58 and 0.78, root mean square differences between 5.6 and 8.3 cm. The virtual stations reproduce the observed tide with errors less or equal to 6.5 cm (i.e. 5.8% or less than the sea level variations of the tide). We show that part of the differences in tides between the two datasets is explained by differences in position between tide gauges and virtual stations. The combined analysis of sea level trends derived from tide gauges and from virtual stations shows how it is an efficient strategy to correct their respective errors and progress towards increasingly accurate sea level trend estimates in a region with little or no research-quality tide gauge data suitable for long-term sea level studies. The conclusion from this study is that in coastal regions poorly covered by tide gauges, our altimetry-based approach can be used to study and monitor sea-level variations related to tides or to long-term sea level changes.

The coast of Cameroon, located at the bottom of the Gulf of Guinea, is confronted with coastal hazards whose magnitude, distribution, and consequences are currently largely underestimated if not poorly understood. This study aims to fill this gap by proposing an integrated approach to coastal vulnerability assessment, combining simple traditional methods, multicriteria AHP (analytic hierarchy process) analysis, and machine learning techniques. Using geospatial data, field observations, and numerical models, we assessed the 402-km Cameroon coastline, taking into account interactions between physical, geological, and socio-economic factors. The results highlight geomorphology, slope, coastal erosion, and population density as the main contributors to vulnerability. The Integrated Coastal Vulnerability Index (IVCI) calculated by the simple method shows variable levels of vulnerability, with a predominance of “very low” and “low” in the northern sectors (S1 = 58

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.

In estuaries environments, the distribution of salinity controls the resourcing of freshwater for agriculture, aquaculture and human consumption; it also regulates the functioning of critical natural habitats. Consequently, there is a particular need for a better understanding of the salinity distribution along river estuaries continuum and for simple predictive relationships linking salinity to estuarine characters and hence environmental conditions. Despite numerous global insightful studies, there are limited studies regarding the spatial patterns of salinity distribution in African estuarine systems. The present study fills this gap using idealized 1-dimentional (1-D) modelling of the Wouri-Nkam River Estuary, Cameroon under various seasonal and tidal conditions. The model results reveal a seasonal tidal excursions varying from 21.4 km (dry season), 18.1 km (transition season), and 14.66 km (wet season). The model performs best during the wet and transition seasons. The year 2050 and 2100 predictions reveal salt intrusion distance of 21 km and 41 km, respectively, indicating that the whole estuary and its surrounding environment will be polluted by marine water in the latter year. The results of this study are important for the region's water resource managers and decision-makers in mitigating the effects of climate change and associated Sea Level Rise (2100 scenario) on the coastal ecosystems since their continuous modification will negatively impact the living standard of Cameroon’s growing population, and the sub region at large.

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.

We study the water-level (WL) evolution in the Douala basin (DB), a sub-basin of the Wouri estuary, separated from the ocean by a natural constriction and influenced by tides and river inflow. Our objective is to assess whether floods in Douala city could result from water overflow from the Douala basin due to Wouri river floods.We first evaluate the constriction’s damping effect by analyzing tide amplitude variations from the ocean to the basin. A simplified model for basin WL variation is developed, incorporating a dissipation parameter (Г) that is evaluated using weak tidal amplitude modulation from the ocean to the basin over the dry season of 2023. Results in the DB reveal nondimensional choking-parameter (P) values of 12 to 19, indicating moderate dissipation. The basin's relatively small area results in a nondimensional river discharge parameter (S) of 0 to 12, indicating high river discharge regimes.Subsequently, the model is used to evaluate the mean and maximum WL, as well as tide amplitude variations of the DB, as functions of river flow and ocean tides. The mean WL increases, but the maximum tide amplitude decreases as river input increases. The maximum WL in the basin always exceeds the maximum amplitude of ocean tides but is only significantly higher when river input is above 1000 m3/s.In current conditions, where maximum observed river input is around 1800 m3/s, it is unlikely that flooding will extend beyond the basin borders into the city of Douala. For a moderate increase (20%) in future maximum river fluxes, it is also unlikely that the DB will overflow into Douala city. Only a drastic increase in mean ocean level and river fluxes (which are possible scenarios associated with climate change) could potentially lead to a significant rise in basin WL, resulting in severe flooding.

The West and Central Africa coastline is highly vulnerable to a range of coastal hazards, due to a combination natural and man-made factors. The scope, distribution, and consequences of these factors are not fully documented, and it can be argued that they are likely underestimated in terms of impact on the region’s human population. To address this shortcoming, an approach based on the use of Geographic Information System (GIS) combined with multi-criteria AHP analysis (analytical hierarchy process), combining geospatial, in-situ observations and numerical modeling, was used to assess coastal vulnerability across 9592 segments along the coast of Cameroon in the Bonny Bay. The most important variables for determining the vulnerability of coastal areas to sea-level are landforms/coastal features, slope and population density. By constructing a spatialised coastal vulnerability index (CVI) and socio-economic vulnerability index (SEVI), it was possible to identify the most exposed areas of the coast according to various levels of vulnerability. The results reveal significant variations from one sector to another. According to the CVI analysis, 67% of the coastal segments present a high to very high risk, mainly in the extreme north and south of country’s coastline (sectors Rio del Rey S1, Cap Cameroun S3 and Sanaga, Kribi, Campo respectively S4 and S5). In contrast, the SEVI show that only around 18% of the Cameroon coast must be considered at high or very high risk, and 60% of the coast is classified as low risk category. By combining the two indices, the integrated coastal vulnerability index (ICVI) was calculated, showing that more than a quarter of the segments are in the high to very high risk category, mainly located in the Cap Cameroun sector S3. This study highlights the amplitude and extent of Cameroons coastal vulnerabilities. The vulnerability maps produced indicate the susceptibility of people living along the coast to coastal hazards. However, it can be used by coastal zone managers and decision-makers to design better coastal zone management plans, and to ensure effective mitigation measures to risk.

The promotion of renewable energy sources, specifically in the photovoltaic sector, is a potential solution to the energy deficit in Central Africa. However, a challenge arises from the unpredictable nature of solar irradiance data, which is subject to climatic variability and difficult to control. The present study pertains to the forecasting of solar irradiance on a tilted surface while accounting for the influence of meteorological factors such as temperature, wind velocity, relative humidity, and atmospheric pressure. The employed technique for this purpose is Artificial Neural Network (ANN), and the investigation is conducted in the urban area of Douala. The instrument utilized to collect the data under investigation in our study is the meteorological station situated at the IUT of Douala. This station was established as part of the Douala sustainable city initiative, in collaboration with the CUD and the IRD. The data was gathered at 30-minute intervals over a span of approximately two years, specifically from January 17, 2019, to October 30, 2020. The aforementioned data has been stored in a database that underwent pre-processing in Excel and subsequently utilized MATLAB for the implementation of the artificial neural network model. The network was trained using 80% of the available data, while 15% was allocated for validation and the remaining 5% was used for testing purposes. Various combinations of input data were tested to determine their respective levels of accuracy. It was determined that the logistic Sigmoid function, utilizing 50 hidden layer neurons, produced a correlation coefficient of 98.883% between measured and estimated solar irradiance. This function is recommended for estimating solar radiation intensities at the studied site and at other locations with comparable climatic conditions.

communication systems have developed significantly over the last few decades. Due to the saturation of lower frequencies of microwave spectrum (3-30 GHz) and the increasing need for high speed, emerging systems for consumer or professional use are progressively shifting to upper microwave and millimeter waves. Our study proposes a methodology for evaluating and classifying losses on a vertically polarized millimeter wave link at 80 GHz. To achieve this, we simulated the link budget of a Nokia 80UBT millimeter wave link operating in its real propagation space (with overground) with Pathloss 5.1 Design tool. Then we built a 3.58 km full-scale link in the Tongo-Bassa watershed of the coastal city of Douala in Cameroon. Analysing data collected over the period from December 06, 2020 to December 16, 2021 under Power BI allowed us to characterize the response of the millimeter signal in free space, during dry and rainy seasons. We then challenge ITU-R P.837-7 and ITU-R.P.838-3 Recommendations on statistical models of rainfall for propagation modeling, especially for millimeter signals propagated in an equatorial climate with heavy rainfalls. The study estimated a rainfall rate for 0.01% of the time at 110.1 mm/h, with a millimeter link cut-off for a rainfall rate greater than 64.8 mm/h, with a specific attenuation due to rain of 6.5 dB/km.

Understanding tidal dynamics in shallow estuaries is of paramount importance to assess the influence of the parameters control them. In the present study, a comprehensive analysis of the tides in the Wouri estuary (Cameroon) was carried out with a high resolution two-dimensional numerical model. Non-stationary harmonic analysis (S_TIDE) and spatio-temporal variation of tidal asymmetry allowed us to quantify changes and tidal asymmetry metrics in the Wouri estuary. A relative sensitivity coefficient (RSC) was introduced to decompose the contribution of tidal amplitude variations to multiple tidal asymmetries. The result reveal an attenuation of the tidal wave as it propagates inland, with a notable reduction in tidal range. This phenomenon is also amplified by the increase in river flow. The positive values of the asymmetry factor confirm a flood dominance in the upper part of the estuary with a pronounced increase upstream. Conversely, ebb dominance with negative values in the lower part of the estuary. The two tidal combinations M2/M4 and M2/S2/MS4 are identified as the main contributors to the tidal asymmetry in the Wouri estuary. These results allowed the Wouri estuary to be qualified as tidal in its lower part and fluvial in its upper part. The evolution of the tidal amplitude and asymmetry may depend significantly on the variations of the river flow and the morphology of the estuary.