In Côte d’Ivoire, agriculture is mostly rain-fed. As a result, changes and variations of climate have considerable impacts on crops production including cotton production. This paper focuses on analyzing the effects of rainfall variations on the cropping season (useful rain season) of cotton in cotton production area of Côte d’Ivoire. A set of stationarity tests was applied to the Nicholson index using rainfall data of the period 1950-2000. Then, from a frequency analyses, the variability of rainfall and characteristic parameters of the cropping season was evaluated in terms of risks. The result shows a general downward trend of rainfall in the cotton growing area with years of breaks between 1964 and 1975. Moreover, spatial evolution of the cropping season parameters is a function of latitude. After the years of breaks, the beginning and the end of the cotton cropping season, which became respectively later and earlier, indicated that the length of useful rain season became shorter. The deficits of seasonal rainfall accumulations vary up to 60%. It is therefore necessary to update the crop calendar by taking into account variability of parameters of the useful rain season.

Ivorian cocoa production, which still remains the driving force of the national economy today, despite the increasingly pronounced diversification of the State's resources, has long benefited from relatively favorable climatic conditions. However, since the 1970s, recurrent disruptions in key rainfall indicators for cocoa production have posed significant risks to the yields and incomes of many Ivorians who depend directly or indirectly on the agronomic performance of this speculation. Using a methodological approach based on descriptive statistical analysis, this study provides an understanding of the evolution of the main climatic factors involved in cocoa production in the Central West, which is one of the country's natural cocoa production basins. To carry out this task, daily rainfall data from Divo and Gagnoa, covering the period 1946-2015, were collected and processed. The results of the various statistical analyses indicate that the seasonal and intra-seasonal rainfall indicators in Gagnoa and Divo are generally declining after the break-up years detected in 1972 in Divo and 1966 in Gagnoa. After the breaks, the Useful Rainy Season (URS) starts later and the ends are earlier than before, which results in a shortening of the length of the URS and a reduction in the intra-seasonal rainfall totals of the two localities. Conversely, the maximum dry sequences during the URS show a slight increase after the break-up dates. The station of Gagnoa was less affected by the rainfall recession than that of Divo where the downward trend in seasonal and intra-seasonal rainfall events is more severe. This makes the Gagnoa region the one with the best rainfall capacities for cocoa production in the study area.

Dekoula et al., J. Appl. Biosci. 2018 Variabilité des descripteurs pluviométriques intrasaisonniers à impact agricole dans le bassin cotonnier de Côte d'Ivoire : zones de Boundiali, Korhogo et Ouangolo ABSTRACTObjective: This study aims to characterize the evolution of agricultural impact intra-seasonal descriptors during the growing season in cotton production area of Côte d'Ivoire. For this purpose, Methodology and results: ten intraseasonal descriptors likely to influence agriculture were determined from rainfall data covering the periods 1951-2000 and 2011-2016 from the Airport, Aeronautical and Meteorological Development and Operations Company and the National Agronomic Research Center. Trend (Mann-Kendall) and stationarity (Pettitt) tests and an inter-period comparison were applied to the identified variables. Analysis of seasonal rainfall accumulations, number of rainy days and average daily rainfall amounts showed a significant downward trend over the period 1951-2000. The cessation and length of the rainy season showed a significant trend towards early onset and shortening respectively. Other intraseasonal descriptors do not varied significantly. In contrast, statistically significant breaks were observed between 1968 and 1979. The period comparison indicated a deterioration in conditions during the dry period . The comparison of the periods indicates a deterioration of the climatic conditions during the dry period . These degradations have increased in the current period (2011)(2012)(2013)(2014)(2015)(2016). Conclusion and application: New climatic conditions observed in the cotton production area translated by a variability of intraseasonal descriptors are making agricultural planning increasingly difficult. It is therefore necessary to update the crop calendars in the cotton production area.

Aims: To understand the role of the interannual variability of cumulative rainfall and maximum dry sequences in cocoa production in the Centre-Ouest, one of the cocoa basins in Côte d'Ivoire, in order to propose technical routes more adapted to current rainfall conditions. Study Design: Collection, analysis and processing of daily rainfall data collected by the rain gauges at Divo and Gagnoa stations. Location and Duration of Studies: Divo Cocoa Research Station of the National Center for Agricultural Research, between January 2017 and June 2019. Methodology: The rainfall regime of each locality was determined to assess the impact of rainfall changes on the seasonality of rainfall. The interannual variability of rainfall was studied from the reduced centred rainfall indices. The break years in the time series were detected at both stations from the Khrono Stat software. The interannual cumulative rainfall were analysed for each station and compared to the minimum threshold allowed for cocoa trees. The means of the maximum interannual dry sequences and their probabilities of occurrence were determined using the agrometeorological software called Instat + Version 3.37. Results: The rainfall regime in the area studied (west-central Côte d'Ivoire) has not been modified by the post-rupture rainfall recession as is the case in other parts of the country; it remains a bimodal system characterized by two rainy seasons and two dries during the year. The Divo and Gagnoa regions have been facing a general recession in rainfall since 1966 in Gagnoa and 1972 in Divo. However, the locality of Gagnoa has experienced an increase in rainfall since 2000. Most of the rupture detection tests identified rainfall rupture dates identical to those indicated by the interannual variability highlighted by the rainfall indices. In Gagnoa and Divo, the interannual cumulative rainfalls after the years of rainfall break are reduced compared to those before these rainfall accidents. This situation has led to an increase in the maximum interannual dry sequences in the departments studied. Conclusion: Local climate change has created difficult rainfall conditions after years of rainfall break for cocoa trees as their water needs are increasingly reduced, especially in Divo in Lôh-Djiboua where the downward trend in rainfall has been continuous since 1972. In Gagnoa since the beginning of this century, there has been a new wet period that allows rainfall to adequately meet the cocoa tree's water requirements.