Gneneyougo Emile Soro

Informal settlements in sub-Saharan Africa often lack infrastructure, and upgrading programmes rarely integrate household sanitation assessment, spatial planning and drainage-flow estimation. This study combines these components in Soussonoubougou, a 49-ha neighbourhood of Bouaké, Côte d’Ivoire. A survey of 350 households conducted in August 2021 found that 67% relied exclusively on wells and 29% used wells alongside rainwater. Stormwater was mainly managed by natural infiltration (65%); where an outlet existed, it was usually the street (92%). Informal dumping was reported by 48% of households, pit emptying was manual in 65% of cases, and 71% of households that had emptied a pit did not know where the sludge was discharged. Using GPS observations, a digital terrain model and CAD/GIS tools, the urban plan was adapted to existing buildings and topography. The proposal includes 600-m² plots, roads of 25, 15 and 10 m, and reserved public-facility plots, and no subdivision of the flood-prone low-lying outlet area in the south. Eighty-four sub-catchments covering 44 ha were delineated from the proposed road and block layout and combined in series and parallel using the Caquot surface method for a 5-year return period. Calculations at 75 nodes and seven outlets produced elementary peak flows of 0.05–1.38 m³/s and a peak flow of about 8.2 m³/s for the 25.7-ha northern collector. The approach provides a practical basis for drainage design, but primary collectors require a 10-year check, and runoff coefficients, relocation needs, solid-waste management and sludge disposal require further assessment.

The rescue of paper pluviographic archives is necessary, but the validation of semi-automatic digitization algorithms for pluviograms remains limited in terms of the number of climatic contexts and types of pluviograms tested. This article applies to the Ivorian pluviographic network. Nine synoptic stations were selected. They cover the four climatic regimes of Côte d’Ivoire. The data come from the archives of the Direction de la Météorologie Nationale of Côte d’Ivoire (DMN) and cover the period from 1955 to 2023, with gaps of varying importance depending on the station. The time series extend from 34 to 55 years. The NUNIEAU software (version 5.01) was used to reconstruct heights at sub-daily time steps. These steps are compatible with risk analysis on small catchments, as is often the case for urban catchments. The daily height totals estimated by NUNIEAU were compared to the visual readings over 24 h performed on the same pluviograms. A total of 31,310 pluviograms containing at least one rainy episode were digitized. Beyond the overall statistics (R² ≥ 0.97 and mean bias < 0.3 mm), the analysis targeting extreme events using physical rainfall thresholds (20, 50 and 100 mm) demonstrates robustness for cumulative totals ≥ 50 mm, the threshold set by the DMN to define extreme events; the absolute bias remains below 0.5 mm for eight out of nine stations, and the coefficient of determination remains ≥ 0.94. These results confirm that semi-automated extraction with the NUNIEAU software correctly restores daily heights. They therefore validate the use of the NUNIEAU software for the Ivorian climatic context (4 climatic regimes) and for pluviograms with curvilinear reference marks. The use of this software is therefore to be promoted for the rescue of paper pluviographic data threatened with disappearance in West Africa, in the continuity of international data rescue efforts carried by the Data Rescue (DARE) initiative.

The study focuses on assessing the individual and combined impacts of climate variability and land use change on hydrological responses. The results indicate that the basin, urban area, cropland, degraded forest, and open forest shows an increasing trend, while gallery forest shows a decreasing trend over the period 1992–2015. Climatic variability is marked by two climatic periods (a wet one from 1980 to 1996 and a dry one from 1997 to 2016) with a 35% decrease in rainfall. Regardless of the state of the landcover used, the simulated mean annual runoff decreases by 67.92% between the wet and dry climate periods. Changes in land use between 1992 and 2015 reduce mean annual runoff by 4.71%. Analysis of the joint effect of climatic and LU variation shows a 68.96% reduction in runoff. In this catchment. The joint impact has a clearly greater effect on runoff than the climatic impact, which is greater than that of human activities. There is a need for policymakers to prioritise sustainable land use practices and integrated water resource management strategies in the area to mitigate the combined effects of climate variability and anthropogenic activities, ensuring the long-term resilience of the ecosystem and water availability for local communities.

Climate change has had strong impacts on water resources over the past decades in Côte d’Ivoire, but these impacts on hydrological extremes remain largely unknown in most watersheds. Thus, this work aimed to evaluate the trends and breakpoints in extreme discharge characteristics of five watersheds in Côte d’Ivoire over the period 1970 to 2017. Seven indexes were selected, namely the 5-day maximum flow (QX5-days), peak discharge (Qmaxan), maximum monthly discharge (VCX30), annual minimum discharge (Qminan), average monthly discharge (QMNA), discharge day rate (VCN7), and characteristic of low discharge (WFD). The analysis was done using the modified Mann–Kendall (MMK) test and the standard normal homogeneity test at a 5% significance level for heterogeneous and homogeneous periods of data. The results for the heterogeneous and homogeneous periods were similar, with a predominance of non-significant trends for high discharge, except for the VCX30 index, which showed a significant upward trend at Kahin station. A decreasing trend for QX5-days was found at Loboville station. The variables Qminan, QMNA, VCN7, and WDF show significant upward trends of 33%, 16%, 50%, and 33% for the heterogeneous stations, respectively. A significant breakpoint in almost all variables was obtained, with a strong decrease after 2008. Some differences between the results from the heterogeneous and homogeneous periods of data were found and discussed. This study can help in understanding the behaviour of past hydrological extremes in the study area and in planning for further studies in the future.

The Aghien lagoon catchment area (365 km²) is largely based on the Ivorian sedimentary basin (68%) and the rest (32%) on the crystalline and crystallophyllous basement. Both coastal and peri-urban basin of the District of Abidjan, the Aghien lagoon watershed is subject to anarchic clearing and increasing urbanization, in addition to being affected by deficient rainfall conditions, since the late 1960s. This watershed, which contains the largest freshwater reserve in the lagoon near the large urban area of Abidjan, has been identified as a potential source of additional drinking water production. The objective of this study is to evaluate the quantitative and qualitative suitability of the waters of this lagoon for the sustainable production of drinking water for the District of Abidjan. In a broader perspective, with the current signs of failure of the water table that supplies the city of Abidjan with water, the Aghien lagoon constitutes one of the ways and one of the hopes for the water supply of the gigantic agglomeration of Abidjan in the years to come, in order to solve the major issues in terms of water resources and drinking water supply, issues that are accentuated by the densification of the population and the effects of the climate change In terms of approach, the aim is to develop, within the framework of WEAP 21 (Water Evaluation and Planning), a decision support system for the sustainable management (current and future by 2050) of this resource through quantitative and qualitative management scenarios, by comparing the evolution of demand to that of supply. This method is based on hydro-climatic data sets and survey data from in situ measurement campaigns; it also integrates a prospective vision of water resources, by extending current trends to 2050, according to alternative scenarios on supply and demand.

The aim of this study is to analyse the spatio-temporal evolution of hydro-rainfall variables in the Agnéby watershed in a disturbed climatic context. Rainfall data from the stations of Arrah, Bongouanou, M’Batto, Akoupé, Céchi, Agboville, Adzopé, Sikensi, Abidjan Airport and Dabou as well as hydrometric data from the stations of Agboville, Offoliguié, M’Bessé and Guessiguié were used. The methodological approach is based on the application of independence and trend tests and spatio-temporal analysis of daily rainfall maxima, duration of consecutive rainfall events, number of rainfall events above a threshold and daily flow maxima. The hypothesis of independence justified the relevance of the choice of variables. The trend test showed the dynamic upward evolution of extreme rainfall and the decrease in the duration of consecutive rainy episodes, in the number of rainy episodes and in the flows feeding the main watercourse. Moreover, spatial analysis of daily maximum rainfall amounts above 120 mm, consecutive maximum rainfall amounts above 160 mm and Gumbel rainfall amounts above 190 mm indicated heavy rainfall in the southern part of the watershed. However, a decrease in rainfall is recorded in the areas covered by the stations of Arrah, Bongouanou, M’Batto, Ce chi and Akoupé. An increase in the flood flow calculated from the Generalized Extreme Value (GEV) between 76.60 m3∙s–1 and 225.70 m3∙s–1 is presented in the main river. The spatio-temporal variation in annual rainfall heights showed a high rainfall in the southern part of the watershed with a decrease in rainfall over the decades (1976–1985 and 1996–2005) followed by an increase over the decades (1986–1995 and 2006–2015). Despite the general decrease in rainfall, extreme rainfall has become frequent, causing flooding in the watershed.

Climate and land use/cover changes are potential drivers of change in hydrology and water use. Incidences of these factors on Bandama hydrological basin and Kossou hydropower generation (1981–2016) in West Africa are assessed in this present work. Using Landsat products of United Stated Geological Survey, results show that water bodies areas and land use have increased by 1.89%/year and 11.56%/year respectively, whereas herbaceous savanna, savanna, forest and evergreen forest coverage have been reduced by 1.39%/year, 0.02%/year, 2.39%/year and 3.33%/year respectively from 1988 to 2016. Hydroclimatic analysis reveals that streamflow presents greater change in magnitude compared to rainfall though both increasing trends are not statistically significant at annual scale. Streamflow varies at least four (two) times greatly than the rainfall (monthly and seasonally) annually except during driest months probably due to land use/cover change. In contrast, Kossou hydropower generation is significantly decreasing (p-value 0.007) at both monthly and annual scales possibly due to water abstraction at upstream. Further works are required to elucidate the combined effects of land use/cover and climate changes on hydrological system as well as water abstraction on Kossou generation.

The Sassandra Basin, like most regions of Côte d’Ivoire, is increasingly affected by droughts that involve many environmental, social and economic impacts. This basin is full of several amenities such as hydroelectric dams, hydraulic and agricultural dams. There is also a strong agricultural activity. In the context of climate change, it is essential to analyze the occurrence of droughts in order to propose mitigation or adaptation measures for water management. The methodological approach consisted initially in characterizing the dry sequences by the use of the SPI (Standardized Precipitation Index) and secondly in determining the probabilities of occurrence of successive dry years using by Markov chains 1 and 2. The results indicate that most remarkable droughts in terms of intensity and duration occurred after the 1970s. A comparison of Markov matrices 1 and 2 between the period considered 1953–2015 with the periods 1953–1970 and 1971–2015 shows a profound change in the distribution of droughts at the different station. Thus, the probability of having two successive dry years is greater over the period 1970–2015 and is accentuated to the Southern and Northern regions (probabilities ranging from 71% to 80%) of the basin. Over the 1970–2015 period, the probability of obtaining three successive dry years is significantly high in this watershed (between 20% and 70%).

Ce travail aborde un problème de santé dû à l’ulcère de Buruli en zone pré-forestière (zone de contact forêt- savane) dans la région de la Marahoué en Côte d’Ivoire. Cette maladie est due à une mycobactérie : la Mycobacterium ulcerans. L’objectif de cette étude est de déterminer des zones à risque à la Mycobacterium ulcerans afin de pouvoir protéger les populations vulnérables. Pour y parvenir, une approche combinée de systèmes d’information géographique et l’analyse multicritère a été adoptée. La cartographie des zones potentielles à risque à l’ulcère de Buruli révèle que le sud de la région présente un risque élevé de la transmission l’ulcère de Buruli. Ce risque élevé est lié à trois types d’indicateurs regroupant les facteurs. L’indicateur lié aux facteurs climatiques (précipitation, température et humidité relative) couvre 41,54% de superficie. L’indicateur lié aux facteurs environnementaux tels que l’indice de végétation (NDVI), l’indice d’humidité du sol (NDWI), l’altitude, l’hydrographie, et à la population, couvre 55,24% et l’indicateur lié à l’occupation du sol couvre 3,22% de la superficie. Par ailleurs, les résultats montrent que 57,17% de la superficie totale de la région est favorable à la transmission de l’ulcère de Buruli. Dans l’ensemble, les indicateurs climatiques, environnementaux, la population et l’occupation du sol constituent des facteurs de risques associés à l’émergence de l’ulcère de Buruli. © 2016 International Formulae Group. All rights reserved. Mots clés: Cartographie, risque, ulcère de Buruli, analyse multicritère, Côte d’Ivoire English Title: Assessment of hydro-climate and environmental risks associated with the Buruli ulcer occurrence in Marahoué region (Côte d’Ivoire) English Abstract This study discusses a health care issue caused by Burili ulcers in pre-forested areas (contact area, forest-savanna) in Marahoué region of Côte d’Ivoire. That disease is caused by a mycobacterium: the Mycobacterium ulcerans. The aim of this work was to determine risk areas to Mycobacterium ulcerans in order to protect vulnerable populations. To achieve this objective, a combined approach of GIS and multi-criteria analysis has been proposed. The mapping of potential risk areas shows that the southern region has a high risk of transmission of Buruli ulcer. This risk is linked to three types of indicators grouping the factors. The indicator related to climatic factors (precipitation, temperature and relative humidity) covers 41.54% of the area. The indicator linked to environmental factors (vegetation index, humidity index of soil, altitude and hydrography) and population covers 55.24% and the indicator for the land use covers 3.22% of the area. Furthermore, the results show that 57.17% of the total area of the region are favorable for the transmission of Buruli ulcer. Overall, climate and environmental indicators, population and land use are risk factors for the emergence of Buruli ulcer. © 2016 International Formulae Group. All rights reserved. Keywords: Mapping, risk, Buruli ulcer, multi-criteria analysis, Côte d’Ivoire

This study aims to assess future trends in monthly rainfall and temperature and its impacts on surface and groundwater resources in the Bandama basin. The Bandama river is one of the four major rivers of Côte d’Ivoire. Historical data from 14 meteorological and three hydrological stations were used. Simulation results for future climate from HadGEM2-ES model under representative concentration pathway (RCP) 4.5 and RCP 8.5 scenarios indicate that the annual temperature may increase from 1.2 °C to 3 °C. These increases will be greater in the north than in the south of the basin. The monthly rainfall may decrease from December to April in the future. During this period, it is projected to decrease by 3% to 42% at all horizons under RCP 4.5 and by 5% to 47% under RCP 8.5. These variations will have cause an increase in surface and groundwater resources during the three periods (2006–2035; 2041–2060; 2066–2085) under the RCP 4.5 scenario. On the other side, these water resources may decrease for all horizons under RCP 8.5 in the Bandama basin.