Abstract 204

Abstract ID: 204

Extreme rainfall events over the French tropical overseas territories : characteristics and atmospheric forcing provided by equatorial waves

Lead Author: Erwan Cornillault
CRNM, France

Keywords: Extreme events, Convectively-coupled equatorial waves, Cluster analysis, French overseas

Abstract: Because they can lead to floods, landslides or rockfalls, extreme rainfall events are often associated with heavy human and economic loss. The early forecast of these high-impact weather events is thus critical for efficient early warning systems. The large-scale atmospheric configurations related to such events have been widely documented over the mid-latitudes. But more studies are needed about those leading to their occurrence over the tropics. In particular, a few case studies emphasised the possible role of convectively-coupled equatorial waves, the major tropical synoptic systems. Still, it remains to be shown that their part is genuinely systematic.
The present study documents the atmospheric configurations leading to extreme rainfall events over the French overseas territories distributed along the tropical belt (Indian Ocean, Western and Central Pacific, and Caribbean Sea). Such documentation should provide a basis to understand better the processes at play in tropical extreme rainfall events. This study also helps to identify large-scale conditions prone to their occurrence and thereby provides further guidance for their improved and earlier forecast, especially at the sub-seasonal timescale.

Using the Météo-France rain gauge network, which provides long-term daily rainfall time series over the French overseas territories, we characterise the properties of extreme rainfall events over these regions, namely their intensity, spatial variability and seasonality. We also assess the contribution of tropical storms and cyclones to their occurrence. Then, hierarchical clustering is used to identify rain gauges consistent in terms of extreme rainfall event occurrence. The composite large-scale atmospheric conditions are finally analysed for each rain gauge cluster, focusing on equatorial waves based on appropriate space-time filtering. We illustrate our approach for La Réunion Island, before evaluating how the results over this area are relevant for the other French tropical regions.

Finally, the potential predictability of the identified atmospheric drivers, with current sub-seasonal forecast systems, is also discussed.

PEYRILLE Philippe (CNRM, France)
COUVREUX Fleur (CNRM, France)
ROEHRIG Romain (CNRM, France)