L’étalement urbain au péril des activités agro-pastorales à Abidjan

L’urbanisation rapide, pose des défis de logement et d’alimentation à la communauté internationale dans son ensemble et particulièrement aux pays en voie de développement. A Abidjan en Côte d’Ivoire, le développement de la commune de Yopougon et la croissance démographique de près de 4 %, entrainent une importante pression sur les terres agricoles urbaines et périurbaines. La présente étude met en évidence l’influence de cet étalement urbain sur les activités agro-pastorales à Yopougon. Une démarche cartographique, suivie d’une démarche socio-anthropologique a été adoptée. Des entretiens avec questionnaires ont été effectués avec 93 agriculteurs. Cette étude montre que les activités agricoles se déroulent sur trois principaux sites : Lokoa, Béago et Azito. Entre 2004 et 2007, les sites agricoles ont connu une réduction d’environ 41 % de leurs superficies du fait de la croissance urbaine. La variation totale de superficie due aux constructions est de 40 % à Azito, 18 % à Lokoa et 8 % à Béago. Des parcs à bétails ont changé de position géographique et se retrouvent en bordure de lagune. L’étude montre également que 94 % des agriculteurs du site vivent principalement de l’agriculture urbaine et que l’insécurité foncière reste leur principale préoccupation. L’étalement spatial de la commune de Yopougon, contribue à une forte réduction des superficies agricoles rendant ainsi vulnérable les familles impliquées dans les activités agricoles comme principales sources de revenus.Rapid urbanization leads to challenges in housing and food access for all the international community and particularly in developing countries. In Abidjan, the developments of Yopougon municipality and population increase have caused significant pressure on agricultural lands and represent a danger for agriculture in the surrounding villages. The present study aims at highlighting the influence of urban spread on agro-pastoral activities in the district of Yopougon. A cartographic approach and a socio anthropologic approach were used. Observations and individual interviews were made with 93 agricultural actors. Agricultural activities were observed on three principal sites : Lokoa, Béago and Azito. Between 2004 and 2007, approximately 41 % of the agricultural surface was occupied by settlements. Total variation of surface due to settlements was 40 % at Azito, 18 % at Lokoa and 8 % at Béago. Some pastoral and cattle parks were joined by the city and were moved to other geographical positions. For 94 % of agricultural actors in the studied site, agriculture was the principal source of income and land insecurity remained the principal concern of the farmers. The urban sprawl of the municipality of Yopougon contributes to a strong reduction of agricultural surface. It makes agricultural actors vulnerable as it is their only source of income

Caractérisation des occurrences de sécheresse dans le bassin hydrologique de la Bia transfrontalier entre la Côte d’Ivoire et le Ghana : contribution des chaînes de Markov

Cette étude analyse l’occurrence au cours de la période 1901-2009 des sécheresses dans le bassin de la Bia en utilisant des modèles de chaînes de Markov. À partir des données pluviométriques annuelles de six stations (Ayamé, Bianouan, Agnibilékro, Enchi, Buakuc et Sunyani), le test sur les tendances séquentielles avec l’indice standardisé de sécheresse pluviométrique a confirmé l’existence de trois grandes tendances durant le dernier siècle. On observe une période humide de 1901 à 1945, suivie d’une période normale de 1946 à 1970, et une période sèche de 1971 à 2009. Une comparaison de matrices de Markov 1 et 2, entre les trois sous-périodes (1901-1945 ; 1946-1970 ; 1971-2009) et la période totale considérée (1901-2009) montre une modification profonde de la répartition des sécheresses dans les différentes stations. L’étude de la persistance de la sécheresse, en utilisant les chaînes de Markov, a montré que la probabilité d’avoir une année sèche après une année sèche est plus importante à partir de 1970 et est accentuée au centre du bassin. La probabilité d’avoir deux années sèches successives est plus importante au nord qu’au centre du bassin. La probabilité d’avoir trois années sèches successives est sensiblement élevée (entre 0, 54 et 0, 70) sur tout le bassin. La période de retour d’une sécheresse aussi longue est comprise entre 10 et 30 ans

Impact of rainfall trends on flood in Agnéby watershed

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

Modeling the Propagation of Flood Waves at the Mouth of the Comoé River in Grand-Bassam (South East of Côte d’Ivoire)

This study was carried out in order to determine the areas at risk of flooding during high water periods at the mouth of the Comoé River in Grand-Bassam. The database is essentially made up of hydro-climatic data, satellite images and topographic data. According to the various criteria, the Weibull law was selected to estimate the maximum frequency flows. According to this law, the flows at the return periods of 2, 10, 50 and 100 years are respectively 634, 733, 781 and 797 m3 / s. The modeling results showed that the areas exposed to the risk of flooding are located near the Ouladine lagoon and the Ebrié lagoon at the mouth of the Comoé river. The extent of the floodplains varies with flooded areas of the order of 85.63 km²; 89.42 km²; 101.67 km²; 107.10 km² for the return periods of 2; 10; 50 and 100 years old

Characterization of Meteorological Droughts Occurrences in Côte d’Ivoire: Case of the Sassandra Watershed

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%)

L’étalement urbain au péril des activités agro-pastorales à Abidjan.

Rapid urbanization leads to challenges in housing and food access for all the international community and particularly in developing countries. In Abidjan, the developments of Yopougon municipality and population increase have caused significant pressure on agricultural lands and represent a danger for agriculture in the surrounding villages. The present study aims at highlighting the influence of urban spread on agro-pastoral activities in the district of Yopougon. A cartographic approach and a socio anthropologic approach were used. Observations and individual interviews were made with 93 agricultural actors. Agricultural activities were observed on three principal sites : Lokoa, Béago and Azito. Between 2004 and 2007, approximately 41 % of the agricultural surface was occupied by settlements. Total variation of surface due to settlements was 40 % at Azito, 18 % at Lokoa and 8 % at Béago. Some pastoral and cattle parks were joined by the city and were moved to other geographical positions. For 94 % of agricultural actors in the studied site, agriculture was the principal source of income and land insecurity remained the principal concern of the farmers. The urban sprawl of the municipality of Yopougon contributes to a strong reduction of agricultural surface. It makes agricultural actors vulnerable as it is their only source of income