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L'article du mois (Mai 2016)

Trends of mean temperatures and warm extremes in Northern Tropical Africa (1961-2014) from observed and PPCA-reconstructed time series.

par Moron V, B Oueslati, B Pohl, S Rome & S Janicot

Journal of Geophysical Research: Atmosphere, in press.


 

 Trends in daily maximum (TX) and minimum (TN) temperatures and indices of warm extremes are studied in tropical North Africa, west of the eastern African highlands, from 1961 to 2014

 

Trends in daily maximum (TX) and minimum (TN) temperatures and indices of warm extremes are studied in tropical North Africa, west of the eastern African highlands, from 1961 to 2014. The analysis is based on the concatenation and cross-checking of two observed databases. Due to the large number of missing entries (~ 25%), a statistical infilling using Probabilistic Principal Component Analysis was applied. Averaged over 90 stations, the linear trends of annual mean TX and TN equal respectively +0.021°C/year and +0.028°C/year.

The frequency of very hot days (TX > 35°C) and tropical nights (TN > 20°C), as well as the frequency of daily TX and TN above the 90th percentile -p90- (“warm days” and “warm nights”), roughly follow the variations of mean TX and TN, respectively. Heat spells of TX or TN > p90 are often short (usually < 2-3 days) and the interannual variation of their mean duration is noisier than for the other indices. Nevertheless, heat spells tend to last longer, with almost constantly positive anomalies since the mid-1990s. The trends in March-June, the warmest season across the Sahelian and Sudanian belts, show similar variations as annual means. Overall, the local-scale warming in annual temperatures, and in March-June, may be viewed merely as a simple shift of the probability distribution function of daily TX and TN. The correlations between the thermal indices and the 2-meter temperatures suggest that the low- frequency (> 8 years) variations may be viewed at least as a regional-scale fingerprint of the global warming, with largest correlations in the tropical Atlantic and Indian basins, while the high- frequency (< 8 years) variations should be mostly viewed as a delayed remote impact of El Nin~o Southern Oscillation (ENSO) events over the region, with warm (cold) anomalies tending to follow warm (cold) ENSO events.

 

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Le Centre de Recherches de Climatologie (CRC) est une équipe de recherche de l'UMR6282 Biogéosciences (CNRS / Université de Bourgogne). Le CRC travaille sur la détection, l'attribution et la prévision du signal climatique et de ses impacts dans l'actuel et le futur. Ses activités sont centrées autour de la régionalisation du climat observé et simulé.

Le CRC est structuré en deux axes thématiques qui mettent en œuvre des méthodes permettant de passer de l'information large échelle (objet des travaux de l'équipe « Dynamique du Climat ») à une information d'échelle plus fine permettant d'évaluer les impacts (équipe « Impacts Climatiques »). Cette méthodologie relève de la statistique (méthodes statistico-dynamiques sur les sorties de modèles; statistiques spatiales;  désagrégation), de l'analyse spatiale (SIG opérateurs d'analyse spatiale vecteur et raster; interpolation spatiale mécaniste ou statistique), ou de la modélisation numérique du climat (modèles régionaux MM5 et WRF, modèle global Arpege-Climat).

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