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Variabilité pluviométrique en Nouvelle-Calédonie et températures de surface océanique dans le Pacifique tropical (1950-2010): impacts sur les incendies (2000-2010)

Abstract : This PhD analyses (i) New Caledonian rainfall variability and its relationships with sea surface temperature (SST) in the tropical Pacific ocean and (ii) the impacts of atmospheric variability on fire activity. New Caledonia shelters a huge biodiversity and stands as one of the current 34 worldwide biodiversity hotspots. Our main goal is to build an empirical statistical scheme for predicting the September to December fires (highest annual frequency). We examined the relationships between fires detected by ATSR and MODIS sensors and local‐scale atmospheric conditions. While the signal in maximum temperature is weak and not robust among the fire records, the local‐scale anomalies of rainfall are always clearly negative for at least 3 months before the fires. These rainfall anomalies are related to warm El Niño Southern Oscillation (ENSO) events and specially to those exhibiting highest SST anomalies in the central Pacific during the austral spring. The warm central Pacific events strengthen the southern Hadley cell around New Caledonian longitudes, with positive rainfall anomalies in the equatorial Pacific leading to an anomalous release of latent heat in the upper troposphere and an increased subsidence in the SW Pacific. Atmospheric anomalies are strongest in September-November because of a combination of a rather strong zonal SST gradient with the warmest SST in the equatorial Pacific just west of the dateline. Moreover, we show that a slight eastward shift of maximum SST during central Pacific events is a crucial point in triggering deep convection near the dateline (west of Niño 3.4). This acts to strengthen deep convection in the central Pacific, thereby providing, a strong modification in the global teleconnections. Squared wavelet coherence between New Caledonia rainfall and Niño 4 SST index shows that their negative correlations are mostly carried by two distinct timescales : the classical ENSO variability and a quasi-decadal one, mainly during the September-November season. This is someway an "ideal" context from the seasonal prediction point of view since the predictor Niño 4 SST index is highly predictable, due to its temporal inertia from austral autumn, and exerts a strong impact on the burned area in New Caledonia. The correlation between the log of observed and simulated (based on Niño 4 index in June-August) total burned area across New Caledonia is 0.87.
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https://tel.archives-ouvertes.fr/tel-00715528
Contributor : Renaud Barbero <>
Submitted on : Sunday, July 8, 2012 - 11:25:45 AM
Last modification on : Saturday, October 3, 2020 - 3:19:53 AM
Long-term archiving on: : Tuesday, October 9, 2012 - 2:30:15 AM

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Renaud Barbero. Variabilité pluviométrique en Nouvelle-Calédonie et températures de surface océanique dans le Pacifique tropical (1950-2010): impacts sur les incendies (2000-2010). Sciences de l'environnement. Université de Provence - Aix-Marseille I, 2012. Français. ⟨tel-00715528⟩

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