The urban community of Epéna, in northern Congo, has been at risk of recurrent flooding for several decades. To this end, the present study aims to analyze rainfall variability from 1980 to 2022 in Epéna and its impact on the rate of flooding observed between October and November 2022. To carry out this study, we used data from the ERA5 reanalyses, consisting essentially of daily rainfall data over the period from January 01, 1980 to December 31, 2022. To this we added sequences of field images. These data were processed according to a methodological protocol based on descriptive statistics and the Pettitt test. The results obtained show that precipitation shows slight fluctuations at monthly and annual, but is highly irregular at seasonal level. The Pettitt test shows a period of change in the distribution of annual precipitation at Epéna between 1908 and 2022. These results also showed that the daily rainfall totals recorded between October and November 2022 at Epéna) were responsible for the floods observed on October 20, 2022 and on November 02 and 29, 2022 Levels.

Les nuages bas sont des composantes cle du climat mais sont rarement bien representes dans les modeles meteorologiques et climatiques. Il a ete montre recemment qu'une importante couverture nuageuse basse se developpe durant la saison seche (juin-septembre) sur la facade atlantique de l'Afrique Centrale, des plaines littorales du Gabon et du Congo-Brazzaville aux plateaux interieurs. Cette saison seche nuageuse est unique sous les tropiques et explique probablement la presence les forets sempervirentes les plus denses d'Afrique Centrale car l'evapotranspiration est faible. Le projet DYVALOCCA est finance sur 2020-2022 par les agences de recherche francaise et allemande (ANR et DFG). Il conduira une campagne de mesures, collectera donnees in-situ existantes et estimations satellitaires afin d'etablir des analyses diagnostiques et de modelisation de la dynamique et la variabilite diurne a interannuelle de ces nuages bas. Ceci devrait aider a comprendre la vulnerabilite passee, presente et future des forets denses sempervirentes d'Afrique Centrale.

An intercomparison of seven gridded rainfall products incorporating satellite data (ARC, CHIRPS, CMORPH, PERSIANN, TAPEER, TARCAT, TMPA) is carried out over Central Africa, by evaluating them against three observed datasets: (a) the WaTFor database, consisting of 293 (monthly records) and 154 (daily records) rain‐gauge stations collected from global datasets, national meteorological services and monitoring projects, (b) the WorldClim v2 gridded database, and (c) a set of stations expanded from the FAOCLIM network, these two latter sets describing climate normals. All products fairly well reproduce the mean rainfall regimes and the spatial patterns of mean annual rainfall, although with some discrepancies in the east–west gradient. A systematic positive bias is found in the CMORPH product. Despite its lower spatial resolution, TAPEER shows reasonable skills. When considering daily rainfall amounts, TMPA shows best skills, followed by CMORPH, but over the central part of the Democratic Republic of the Congo, TARCAT is amongst the best products. Skills ranking is however different at the interannual time‐scale, with CHIRPS and TMPA performing best, though PERSIANN has comparable skills when only fully independent stations are used as reference. A preliminary study of Southern Hemisphere dry season variability, from the example of Kinshasa, shows that it is a difficult variable to capture with satellite‐based rainfall products. Users should still be careful when using any product in the most data‐sparse regions, especially for trend assessment.

Maximum and minimum temperatures time series of Congo-Brazzaville are analyzed for trend and discontinuities over the period 1932 to 2010. Temperatures series show an irregular increase. A total of 8 synoptic stations show positive trends in their annual mean maximum temperature series, and 7 of them are significant, with higher trends for urban stations. Annual mean minimum temperature showed 6 stations having positive trends. This increase is in relation with observations at regional scale. However, the differences are observed between large towns (Brazzaville and Pointe-Noire), and small or rural towns (Dolisie, Sibiti, Impfondo, Djambala). Trends in diurnal temperature range (DTR) are large positive trends in maximum temperature that are mainly observed in cities. The curve of DTR shows a decreasing trend which indicates the increasing of minimum temperatures. The effects of urbanization on temperature trends are investigated. Most stations regarded as urban stations are still useful for trend analysis; being situated on the suburban of the studied cities, they are therefore, not substantially influenced by the urban heat island.

The interannual variability of rainfall amounts and rainy days is analysed from synoptic stations located in different climatic zones of Congo-Brazzaville over the common period 19322007. The annual and seasonal rainfall evolution is appreciated using standardized indices. Trends examined were based on the non-parametric Mann-Kendall test (the major synoptic stations point out alternative periods of anomaliespositive and negative). A majority of negative anomalies is recorded during the 1930s and 1940s. The decade 1950 shows mainly positive anomalies with the exception of 1958 which records a general precipitation deficit all across Congo. The decade 1960 is characterized by precipitation excess over the whole Congo. The decades 1980 and 1990 experience the largest rainfall deficit (about 1020% below the long-term mean). The evolution of the precipitation at Brazzaville is particularly stable, although there are large positive anomalies during the 1990s. The transition between positive and negative anomalies decades is not uniform across Congo. The progressive non-parametric Mann-Kendall trend test shows that there is stability in the annual rainfall and rainy days over the southern area in the period 19322007. By contrast, the annual rainfall for the northern stations shows a significant decline since about the 1980s. In the south the decline is observable only in the evolution of the MarchMay seasonal rainfall. In most of the stations there is a precipitation increase during the September-November rainy season. Copyright (c) 2011 Royal Meteorological Society

Trend and discontinuities in rainfall and temperature time series for Congo-Brazzaville are analysed over the period 1950–1998. Rainfall series show a stationary evolution in the south, and an overall negative trend in the north, while temperature series present an irregular increase. This increase is in relation with observations at the regional scale. After a stationary period, a main discontinuity occurred between 1968 and 1970, followed by a second at the beginning of the 1980s. However, the differences are observed between large towns (Brazzaville and Pointe-Noire), and small towns (Dolisie, Sibiti, Impfondo).

Application of the Markov process for daily precipitation occurrences in Congo-Brazzaville. This study deals with the daily precipitation occurrence during the rainy season in different locations in Congo-Brazzaville. The Markov-chain probability model has been used for defining probable dry and wet rainy sequences at each station, and transition probabilities between daily precipitations of two successive days. The main results are: in Congo, the dependence on the preceding day of the daily precipitations occurrence; the confirmation of two main climatic region (equatorial climate to the north and tropical wet to the south): the lack of coherence in the distribution of precipitations. To cite this article: G. Samba, M. Mpounza, C R. Geoscience 337(2005). (c) 2005 Academie des sciences. Publie par Elsevier SAS. Tous droits reserves.

Sur la periode 1951-1990, le bilan hydrique potentiel est negatif en moyenne pendant la saison seche de juin a septembre dans toute la region du Pool, situee au sud de la Republique du Congo, alors que des valeurs positives sont observees au cours de la premiere saison des pluies. Pour 8 annees sur 10, les stations de Brazzaville et de M’pouya affichent un bilan negatif, alors que tout le reste du pays connait un bilan positif. L’evolution de la defience hydrique pendant le mois de septembre permet de distinguer la moitie du nord (ou le mois de subsec) de la moitie sud (ou il est sec). Nos resultats precisent la repartition spatiale du potentiel hydrique et devraient permettre une meilleure gestion des bas-fonds ainsi que du calendrier agricole.