Abstract
AbstractIn 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.
Highlights
Agricultural production in the tropical zone is highly dependent on several environmental factors, especially water availability (Wallace 1991; Meinke and Stone 2005)
The main objective of this work is to propose a new approach to define onset/cessation dates and monitor their interannual variability, which would be minimally sensitive to parameterization and local-scale contingencies but still has some significance at local scale
The main objective of this paper is to present a new approach of extracting the regional-scale signal contained in rainy season onset and cessation dates defined at the local scale and based on multiple combinations of rainfall parameters
Summary
Agricultural production in the tropical zone is highly dependent on several environmental factors, especially water availability (Wallace 1991; Meinke and Stone 2005). Agroclimatologists usually define the onset at the rain gauge scale, using a variety of empirical thresholds (Stern et al 1981; Sivakumar 1988; Moron et al 2009; Marteau et al 2009) They consider that the rainy season onset is the first wet day of a spell receiving a given rainfall amount and not followed by a long dry spell during the subsequent weeks. The rainfall thresholds are determined empirically in order to fit the requirements of a given crop and are adjusted to account for local-scale climatic conditions (e.g., lower potential evapotranspiration in cool, high-altitude areas than in warm areas). These local-scale ‘‘agroclimatic’’ onset definitions are rigid in so far as each threshold may not be transposable to other crops and other
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