Socio-economic study of rice-fish farming in the region of upper Sassandra (Côte d'Ivoire)

This study aims to assess the socio-economic impact of rice-fish farming in the Haut Sassandra region. To this end, a survey was conducted in five villages in the sub-prefecture of Bédiala between April and July 2020 using a questionnaire. The method of collecting data and other information consisted of direct interviews with the leaders of the Bédiala fish farmers’ association (DEHIZEA), producers and fishmongers. The information thus obtained was supplemented by direct observations in the field. On the basis of the data collected on rice-fish farmers from DEHIZEA officials, 60 (or 30 %) rice-fish farms were selected out of 202 farms with effective fish farming activity in the areas concerned. The selection was made jointly with DEHIZEA officials using the simple random sampling method. The XLStat 2016 program was used to process the quantitative data. The results show that 63.3 % of rice-fish farmers are farmers and have been practicing the activity for more than 5 years. The sale of fish is the main activity of 80% of fishmongers. In 86.7 % of cases, rice bran constitutes the food distributed to the fish. The fish production of 40% of the rice-fish farmers is between 0.5 and 1.5 tonnes. Concerning rice production, 43% of rice-fish farmers produce between 500 and 1200 kg and 31% produce between 500 and 900 kg. On the other hand, all the rice-farmers have a production of less than 6 tonnes/year. They sell this production between 500 and 1000 CFA francs/kg, which gives an annual income of less than 5 million CFA francs. Ninety-seven percent of the producers are satisfied with the financial contribution of the system.Keywords: Rice-fish culture, Socio-economic, Upper Sassandra, Côte d’Ivoir

Changes in Vegetation and Rainfall over West Africa during the Last Three Decades (1981-2010)

The decadal variability of rainfall and vegetation over West Africa have been studied over the last three decades, 1981-1990, 1991-2000 and 2001-2010 denoted as 1980s, 1990s and 2000s, respectively. Climate Research Unit (CRU) monthly precipitation and Normalized Difference Vegetation Index (NDVI) from the National Oceanic and Atmosphere Administration (NOAA), all covering the period 1981-2010 have been used. This study aimed to assess the changes in the land surface condition and the spatio-temporal distribution of rainfall over West Africa region. The relationship between rainfall and vegetation indices over this region was determined using Pearson’s correlation. Also, the decadal comparison between rainfall and NDVI over the region was based on the significant t-test and the Pearson’s correlation. Results showed that significant return to wet conditions is observed between decade 1980s and decade 1990s over West Africa, and also during decade 2000s with the exception of central Benin and the western Nigeria. Meanwhile, a regreening of the central Sahel and Sudano-Sahel regions is noted. From 1990s to 2000s, this regreening belt is located in the South and the coastal areas: the Guinea Coast, Sudano-Guinea and western Sahel regions. A northward displacement of this re-greening belt is also detected. Thus, a linear relationship occurs between rainfall and NDVI in the Sudanian savannah region, but it is not the case in the rest of West Africa. This may suggest that the re-growth of vegetation in the Sudanian savannah region may be linked to rainfall supplies. Therefore, re-greening over Sahel region in1990s is related to rainfall recovery. However, this re-greening was not sustained in the decade 2000s due to a slight decrease in rainfall

Rainfall risk over the city of Abidjan (Côte d'Ivoire): first contribution of the joint analysis of daily rainfall from a historical record and a recent network of rain gauges

Every year, rains cause material damage and human losses, in Abidjan (Côte d'Ivoire). The objective of this study is to contribute to the characterization of the rain hazard in the District of Abidjan. The available data are made up of daily rainfall from a historical station “Abidjan airport” (1961–2014) and an academic network of rain gauges (21) progressively implemented in Abidjan since 2015. A descriptive analysis (date of occurrence, rainfall depth, mean wet days intensity and number of rainy days) on the Highest Cumulative Rainfall Periods (HCRP: 60 d) is conducted on the long-term station. The periods of highest risk of flooding during the long and short rainy seasons are characterized. The Experimental variograms of extreme rainfalls derived from the current network, allow to evaluate their extensions according to the rainy season.</p

Semi-analytical method for designing finite sets of discriminated solitons and soliton molecules in fibres

International audienc

Climate change impact on agricultural production: the case of Comoe River basin in Ivory Coast

International audienceThe objective of this study is to evaluate the impact of climate change on the hydrological balance of the Comoe basin, an area of rainfed agriculture. Frequency analysis of cropping seasons, with estimation of cumulative water deficit through a daily water balance simulation (1950\textendash2000), was used to explore the impact of variation in climate conditions on the cropping season. The performance indicators show an uneven evolution of agroclimatic potential: in a unimodal regime centred on the north of the basin, the cropping season duration, which did not change significantly, is consistent with the small changes in onset and end dates to that season; however, the cumulative water deficit increased from 750 mm to more than 850 mm. In contrast, in the bimodal regime, the western fringe, while less affected by both the recession and the rainfall deficit, undergoes an unusually short duration of cropping season. Thus, the second cropping season no longer lasts 90 days and seems less compatible with some cropping cycles. Such drought could increase the risk in annual cereal production without, however, being a leading limiting factor. Editor Z.W. Kundzewicz; Guest editor D. Hughe

Origins of streamflow in a crystalline basement catchment in a sub-humid Sudanian zone : the Donga basin (Benin, West Africa) Inter-annual variability of water budget

During the last quarter of the 20th century, West Africa underwent a particularly intense and generalized drought. During this period, the biggest drops in streamflow were observed in the Sudanian zone rather than in the Sahelian zone, but the reasons are still poorly understood. In 2000, a meso-scale hydrological observatory was set up in the sub-humid Sudanian zone of the Upper Oueme Valley (Benin). Three embedded catchments of 12-586 km(2) located on a crystalline bedrock were intensively instrumented to document the different terms of the water budget and to identify the main streamflow generating processes and base-flow mechanisms at different scales. Geophysical, hydrological and geochemical data were collected throughout the catchments from 2002 to 2006. Crossing these data helped define their hydrological functioning. The region has seasonal streamflow, and the permanent groundwater in the weathered mantle does not drain to rivers, instead, seasonal perched groundwaters are the major contributor to annual streamflow. The perched groundwaters are mainly located in seasonally waterlogged sandy layers in the headwater bottom-lands called bas-fonds in French-speaking West Africa of 1st order streams. During the period 2003-2006, regolith groundwater recharge ranged between 10% and 15% of the annual rainfall depth. Depletion of permanent groundwater during the dry season is probably explained by local evapotranspiration which was seen not to be limited to gallery forests. During the 4-year study period, a reduction of 20% in annual rainfall led to a 50% reduction in streamflow. This reduction was observed in the two components of the flow: direct runoff and drainage of perched groundwater. Thanks to the comprehensive dataset obtained, the results obtained for the Donga experimental catchment are now being extrapolated to the whole upper Oueme valley, which can be considered as representative of sub-humid Sudanian rivers flowing on a crystalline basement, for example, the upper courses of several major West African rivers (Senegal, Niger, Bani, and Volta)

Contrasted land-surface processes along the West African rainfall gradient

We review the main results of land-surface studies obtained in the three sites of the long-term observing system AMMA-CATCH. Runoff in the Sahel enhances the variability of energy partitioning between non-infiltrative areas where sensible heat is dominant and infiltrative areas where soil water availability increases the latent flux. In terms of water resources, an increase in runoff over the past 50 years, already reported for the exoreic Sahel, was revealed in the endoreic Sahel. In the Sudanian domain, the subsurface origin of streamflow could explain its decrease over the same period. Copyright © 2011 Royal Meteorological Society