Extreme rainfall events are meteorological hazards that cause great damage and many casualties in the world. This paper examines the trends in extreme rainfall from 10 sub-daily time series and 44 daily time series in Côte d'Ivoire. Rainfall data were converted into indices. In total, six (6) indices were used for daily extreme rainfall and one (1) index for sub-daily extreme rainfall (15 to 240 min). Two statistical tests for trend detection were used to evaluate the possible trend in these precipitation data. The first is a Mann-Kendall non-parametric trend test, used to evaluate the existence of monotonic trends. The second is a linear regression method, based on a parametric approach to trend detection. Results show that very few statistically significant decreasing trends can be detected at the sub-daily and daily timescales. Some decreasing trends in extreme rainfall events were localized in the south and southeast. These results could enhance the implementation of adaptation systems to flood risk.

Résumé Cette étude évalue les conséquences de la variabilité climatique sur la maïsiculture pluviale dans l'est Ivoirien. Les tests de stationnarité ont mis en évidence des ruptures dans les séries pluviométriques à la fin des années 1960. L'impact de ces décrochages sur les saisons culturales montre que, malgré sa réduction après les années 1970, la durée de la première saison culturale ne constitue pas un facteur restrictif pour la maïsiculture de cycle court. L'évolution des conditions hydriques de la maïsiculture et les potentiels de rendements induits ont été simulés sur la base des données climatiques et des résultats d'essais de longue durée. Les conditions hydriques ont été caractérisées en termes de déficit et d'excès d'eau par le modèle CROPWAT-FAO de simulation du bilan hydrique. La confrontation des résultats des simulations et des indicateurs descriptifs des tendances de production, montre que l'état actuel des conditions climatiques n'explique pas la dynamique d'ensemble de la maïsiculture dans l'est Ivoirien.Mots clefs pluie; variabilité climatique; maïsiculture pluviale; bilan hydrique; rendement du maïs; Côte d'Ivoire Climate variability and rainfed maize production in the eastern Ivory CoastAbstract This study examines the impact of climate variability on rainfed maize production in the eastern part of the Ivory Coast. Stationarity tests show breaks in the annual rainfall regimes toward the end of the 1960s. The impact of these jump changes on the growing seasons shows that, despite significant decrease in its length after the 1970s, the main growing season remained long enough to crop maize with a short cycle. The impact on maize was assessed by simulating yields and crop water use. The simulation was based on long yield series and meteorological data using the FAO CROPWAT program to calculate water deficit and excess water conditions. The comparison of simulation outputs with the indicators for trends in production, shows that the current state of the climatic conditions does not explain the overall dynamics of maize cropping in the eastern Ivory Coast.

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The objective of this study is to assess the impact of climate change on the evolution of the hydrological balance of the Comoe basin, an area of rainfed agriculture. Starting from a frequency analysis of cropping season with an appraisement of cumulative water deficit through a daily water balance simulation, the study explores the impact of climate conditions evolution over the cropping season periods from 1950 to 2000. The agroclimatic performance indicators thus defined, particularly the satisfaction index of crop water requirements (CWRI) and the annual amount of water deficits, show up a disparate evolution of agroclimatic opportunities: in the case of unimodal regime in the north, the cropping season duration did not vary significantly. Those weak variations match strongly with those of the onset and end dates of that cultural season; however, the water deficit heaped up increased from 750 to more than 850 mm. The bimodal regime of the western fringe is less affected by the rainfall reduction, meanwhile we notice a slight water deficit decrease combined with cropping seasons (CS) reduced abnormally. The second cropping season no more reaches 90 days and seems thus less compatible with some cropping cycles. Such a drought will increase the risk for annual crops production without being however a leading limited factor. Impact du changement climatique sur la production agricole: le cas du bassin du fleuve Comoé en Côte d'IvoireRésumé. Cette étude évalue l'impact des changements climatiques sur les conditions hydriques du bassin de la Comoé, une zone d'agriculture pluviale conventionnelle. L'analyse fréquentielle des saisons culturales et l'estimation des déficits hydriques par simulation du bilan hydrique , permet de montrer une évolution disparate des potentialités agroclimatiques : en régime unimodal centré sur le secteur nord du bassin, la durée de l'unique saison culturale qui n'a pas fondamentalement changé, concorde avec les faibles variations des dates d'apparition et de fin de celle-ci; le déficit hydrique passe toutefois de 750 à plus de 850 mm. En régime bimodal en revanche, la frange occidentale peu affectée à la fois par la récession pluviométrique et le déficit hydrique, subit une durée anormalement réduite des saisons culturales ; ainsi, la deuxième saison culturale n'atteint plus 90 jours, et semble de moins en moins compatible avec certains cycles culturaux. Une telle sécheresse pourrait augmenter les risques de production en céréales annuelles, sans toutefois constituer un facteur limitatif de premier plan. Downloaded by [FU Berlin] at 17:38 24 June 2015A c c e p t e d M a n u s c r i p t 2 Mots clés agriculture pluviale ; bilan hydrique ; saison culturale ; déficit hydrique ; bassin de la Comoé ; Côte d'Ivoire

The rainfall variability observed since the 1970s has resulted in a succession of years of drought. Generally, this has raged for thirty years in West Africa, in the Sahelian countries, and the countries along the Gulf of Guinea. It has resulted in severe decreases in rainfall and stream flows. This paper focuses on taking into account the rainfall variability on surface flows of the Agnéby watershed to better understand the evolution of the hydrological regime. To achieve this, the study was based on daily rainfall and flow data from 1955 to 2015. An analysis of the hydropluviometric indices has been performed. These indices associate several complementary methods such as the detection tests of the break in the average, the procedure for the segmentation of hydrological time series, the runoff coefficient, and the hydroclimatic average coefficient. The analysis reveal ruptures around 1960s and 1980s. These result in hydrological responses with deficits of-54% and-36%. A significant resumption of the average flows is observed from 1996, with a rainfall surplus of + 7%, which has resulted in a hydrological response of 149%. This latter finding points out the entry into a new, more humid climatic period than that of the 1960s and 1980s at the scale of the Agnéby basin. This is confirmed by the increase of the hydroclimatic average coefficient up to 130% since the end of the 2010 decade. The annual rainfall obtained are also well comparable with those of the wet period (1997-2015) with a cumulative rainfall varying between 1280 mm and 1760 mm.