Article InfoStochastic weather generators used in meteorological and hydrological studies are mostly statistical models that produce random numbers resembling the observed data on which they have been fitted. They can generate weather sequences that statistically resemble the real observed data. In this study we developed a single-site daily rainfall generator for the simulations of rainfall occurrences and amounts in northwestern of Benin. A first-order two-state Markov chain was used to determine the occurrence of daily precipitation. The rainfall amounts on wet days were generated by using the oneparameter Exponential distribution and the two-parameter Gamma distribution. The Markov model was successful in simulating the rainfall occurrences and the Exponential distribution as the more reliability in preserving most of the important daily characteristics of the historical rainfall amounts. The test of the two distributions on data that are not taken into account in the elaboration of the model has shown that the exponential distribution reproduces well the statistics of the daily precipitation than the gamma distribution
The recurrence of flooding in recent years in West Africa is dramatically affecting the socio-economic system of most countries in the region. This work is devoted to the analysis of the heavy rains of its last years in the context of global warming in subequatorial Benin through eight rainfall indicators. For this purpose, the daily rains collected at seventeen stations in the south of Benin between 1960 and 2018, the maximum and minimum daily temperatures of the two synoptic stations in the study area between 1970 and 2018 are used. Analysis of the results shows a non-uniform trend in rainfall indicators over the entire study period. The monthly trend is in accordance with the bimodal rain regime of southern Benin for each of the climatic indicators studied. After the break in the downward trend in rainfall in the 1980s or 1990s at the various stations, the last three decades have been marked above all by ten-year averages of the various indicators that are higher than those obtained over the entire study period. Despite the low proportion of extreme rains, their frequency has increased since the resumption of rainfall in the 1980s or 1990s, especially compared to the 1970s and 1980s. The highest heights are observed for the most part in the towns close to the sea Atlantic Ocean. Global warming in southern Benin is characterized above all by high decadal temperature variation rates in the 1990s. This significant global warming in this pivotal decade is accompanied by relatively large growth in all indicators in southern Benin.
Four indices were used to assess changes in both cold and hot tails of the daily temperature distributions. The analysis is based on long-term daily maximum and minimum temperature spanning the period from 1970 to 2015. The linear trend in the derived temperature indices was computed using the ordinary least squares (OLS) method. The significance of the trend was assessed using the Mann-Kendall test. Results showed significant changes in temperature extremes corresponding to a warming, especially for cold nights and warm nights. The results indicate a significant decrease in the frequency of cold nights (trend = -14.2 days/decade) and a significant increase in the occurrence of warm nights (14.6 days/decade). Daily maximum temperature indices showed similar changes but with smaller magnitudes.
Changes in the frequency and timing of extreme precipitation in southern Benin are assessed in the context of global warming. The peak-over-threshold (POT) is used for this purpose, with the six (06) year return period daily rainfall as the threshold over seventeen (17) weather stations between 1960 and 2018. The results show that the South Benin experienced extreme rainfall on many occasions between 1960 and 2018 with a nonuniform spatiotemporal distribution of this category of rainfall. No statistically significant trend in the frequency and variation of extreme rainfall intensities is revealed over the study period. Despite the low rate of extreme rainfall, the monthly trend is consistent with the bimodal rainfall regime in southern Benin. The global warming highlighted in its last decades in southern Benin is accompanied by a slightly upward trend in extreme rainfall compared to the period before 1990.
Le potentiel érosif de la pluie est sa capacité à provoquer l’érosion du sol. Son étude s’appuie sur l’énergie cinétique (KE) de la pluie qui peut être obtenue à partir de la distribution granulométrique des gouttes de pluie (en anglais Drop Size Distribution : DSD). Ce travail propose deux stimateurs de l’énergie cinétique de la pluie (KE) au Nord-Ouest du Bénin, l’un à partir de l’intensité de pluie (I) et l’autre à partir du facteur de réflectivité radar (Z) dans l’approximation de Raleigh. Les deux relations climatologiques KE-I et KE-Z sont établies à partir des données de DSD mesurées sur trois sites au Nord-Ouest du Bénin. L’énergie cinétique de la pluie a été évaluée par l’utilisation des relations KE-Z et KE-I. Ainsi, il est noté que la relation KE- Z est plus performante que la relation KE - I. Par ailleurs, en évaluant la sensibilité de ces relations KE- I et KE - Z au pas de temps d’intégration des spectres de DSD, il ressort que la performance de ces relations augmente avec le pas de temps d’intégration.
La distribution granulométrique de la taille des gouttes de pluie joue un rôle crucial dans l’étude de la microphysique des précipitations, l’érosion des sols et la télécommunication. Elle est souvent modélisée par les lois exponentielle, lognormale, gamma standard ou gamma généralisé. Jusqu’à présent en Afrique de l’ouest, la distribution granulométrique de la taille des gouttes de pluie est modélisée par la loi gamma ou lognormale. La présente étude s’est intéressée à la modélisation de la distribution par la loi gamma généralisée normalisée par un double moment. Les données exploitées sont les spectres de gouttes de pluie de durée une minute de la ligne de grain du 25/07/2006. Elles ont été recueillies au cours de la campagne AMMA à Djougou (Nord-Ouest du Bénin) en 2006. Les résultats obtenus montrent que la loi gamma généralisée normalisée par un double moment estime mieux les moments que la loi gamma standard normalisée par un double moment proposé par Moumouni et al., 2008.
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