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

par Joseph Boyard-Micheau; Pierre Camberlin; Nathalie Philippon; Vincent Moron.

à paraître dans Journal of Climate

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 mm without a dry spell lasting n days and receiving less than p mm 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 regional scale. This new approach is less sensitive to parameterization and local-scale contingencies but which has still some significance at 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.

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

par Joseph Boyard-Micheau; Pierre Camberlin; Nathalie Philippon; Vincent Moron.

 

à paraître dans Journal of Climate

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 mm without a dry spell lasting n days and receiving less than p mm 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 regional scale. This new approach is less sensitive to parameterization and local-scale contingencies but which has still some significance at 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.