Regional-scale rainy season onset detection: a new approach based on multivariate analysis.

Joseph Boyard-Micheau (1) , Pierre Camberlin (1) , Nathalie Philippon (1) , Vincent Moron (2, 3)

1 BGS - Biogéosciences [UMR 6282]
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 IRI - International Research Institute for Climate and Society

In agroclimatology, the rainy season onset and cessation dates are often defined from a combination of several empirical rainfall thresholds. For example, the onset may be the first wet day of N consecutive days receiving at least P millimeters without a dry spell lasting n days and receiving less than p millimeters in the following C days. These thresholds are parameterized empirically in order to fit the requirements of a given crop and to account for local-scale climatic conditions. Such local-scale agroclimatic definition is rigid because each threshold may not be necessarily transposable to other crops and other climate environments. A new approach is developed to define onset/cessation dates and monitor their interannual variability at the regional scale. This new approach is less sensitive to parameterization and local-scale contingencies but still has some significance at the local scale. The approach considers multiple combinations of rainfall thresholds in a principal component analysis so that a robust signal across space and parameters is extracted. The regional-scale onset/cessation date is unequally influenced by input rainfall parameters used for the definition of the local rainy season onset. It appears that P is a crucial parameter to define onset, C plays a significant role at most stations, and N seems to be of marginal influence.

Mots clés: Intraseasonal variability; Interannual variability

Domaines: Climatologie; Milieux et Changements globaux

Joseph Boyard-Micheau, Pierre Camberlin, Nathalie Philippon, Vincent Moron. Regional-scale rainy season onset detection: a new approach based on multivariate analysis.. Journal of Climate, 2013, 26 (22), pp.8916-8928. ⟨10.1175/JCLI-D-12-00730.1⟩. ⟨hal-00908347⟩