INFLUENCE OF THE ENSO PHENOMENON ON PRECIPITATION IN THE NORTH-WESTERN PART OF MADAGASCAR

climatology

This article is based on an analysis of precipitation according to ENSO phenomenon. Self-organizing maps, associated with hierarchical ascending classification, are methods for subdividing our study area. The calculation of the standardized precipitation index is applied to our rainfall data. The anomalous accumulation is used to determine the start dates and end dates of the season. The aim is to characterize the spatio-temporal variability of rainfall in the north-western part of Madagascar. Then, detect during which ENSO phases most often occur the precipitation anomalies (state of humidity or drought) and also the length of the longest or shortest season. The study area is located between longitudes 43°E to 48.5°E and latitudes between 12°S to 18°S. It is subdivided into 3 sub-zones. The daily precipitation data used are available on the ECMWF website for a period of 42 years (1979 to 2020). They correspond to the sum of large-scale precipitation and convective precipitation. Our study area is grouped into three different sub-areas. The maximum amount of precipitation during the La Nina phase does not differ significantly from that observed during the El Niño phase. However, the El Niño episode has more influence on annual precipitation in our study region. In subzone 2, extreme humidity occurred during this phase. Furthermore, the amounts of annual precipitation during the El Niño phase are almost greater than those in La Nina years. On the other hand, the neutral phase often evokes a state of precipitation close to normal. In subzones 1 and 3, the length of the season curiously tends to lengthen during the El Niño phase.

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