Malagasy Climate Variability, Characteristics, Modes, Mechanisms, Modelling, Teleconnection and Prediction
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Date
2009-12
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Addis Ababa University
Abstract
Actually, the water resource becomes increasingly limited and difficult to exploit.
Their quantity on the Malagasy territory is unevenly spread; it is relatively abundant in the
East coast while the area of South-east presents a periodic situation vulnerable to the dryness.
The water resource is especially conditioned by precipitations in the form of rain having a
great effect in society’s life.
Prior to different tasks linked to the Malagasy rainfall, better understanding of the
meteorological and orographical influences are very useful as Madagascar is situated in the
southwest zone of the Indian Ocean closed to the African continent with a channel sea on the
West (Channel of Mozambica) and the Indian Ocean on the East, located between 12° and 25°
30' of southern latitude, crossed by the austral Capricorn tropic. It is an Island whose
transversal profile of its orography is marked by a strong asymmetry of slopes: in the East,
the altitude rises quickly and reaches the central areas through a sharp cliff. Its Eastern coastal
plains are very narrow. However, in the West the relief declines progressively attaining low
stretched areas.
In the synoptic scale, tropical weather is prevailing in this island with dry season
during the austral winter (May to October) and wet season during the austral summer
(November to April). Strong trade winds and extra tropical perturbations are the most
dominant meteorological patterns prevailing in the island.
Despite the establishment of the rainfall climatology over Madagascar gaps are still
identified in that previous analysis for instance the spatial and temporal variation rainfall with
tremendous spatial gradient of rainfall in all directions. It is therefore vital to optimally
compute space-time modes of variability of the country by the mean of the Principal
Component Analysis (PCA) as this type of research is not yet attempted for Madagascar
despite its popularity. Most importantly, salient factors that determine these modes are
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investigated to better understand the rainfall mechanisms in the country using the worldwide
PCA tools.
Therefore, tropical cyclone having mutual relationship with the leading mode
component opens an interesting research field on the role of tropical cyclone in the
modification of Madagascar climate and its contribution in different regions during the rainy
season.
Furthermore, extreme precipitation events in Madagascar can be related to a variety
of catastrophic events including drought, famine, flooding, and the spread of disease. It is
important to attempt to anticipate when these extreme events are likely to (Doncques, 1975)
occur so that disaster relief efforts can be implemented which could reduce the potential
impacts of these extreme events. In order to predict and prepare areas that may be susceptible
to food shortages as a result of rainfall anomalies, SPI (Standardized Precipitation Index) and
EV (Extreme Value) Analysis applied to the precipitation records are adopted. Specifically,
the aim is not only to study the quantile of Madagascar rainfall record but also its tails and
risk measures using the Extreme Value theory. Another important issue of this analysis is the
return level of the excess of the precipitation record in order to extract the main temporal
pattern of severe rain which occurred in Madagascar.
As a crucial natural resource for Madagascar, rainwater is unevenly distributed.
Some regions are extremely ‘fragilized’ by the cyclone passage that provokes important
floods. Other areas are recurrently hit by drought especially the southern part of the country,
but in the other regions it seems periodic. In fact, the extreme South of the island is a semiarid
area where the annual average precipitation is less than 600 mm with 9 to 11 months
water deficiency. So, whatever classification adopted and criteria employed, the South
remains as the driest region (Doncques, 1975). This study is devoted to understanding the
dynamics of dry events in the atmosphere over the southern part of Madagascar. The study
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reveals that Southern Madagascar rainfall during the austral summer season depends on
quantitative dynamical atmospheric variables. It is with this simple conceptual framework that
we manage to predict the seasonal mean rainfall during its active phase on the relative
contribution of these externally forced components. Moreover, it is important to develop an
early warning system for rainfall variability based on a sound scientific understanding of its
causes. This step of analysis considers which components of the ocean-atmosphere system
contribute to its water resource then it compares the predicted result by model with the
observed datasets of southern rainfall. Finally, it is aimed to give contribution to the
predictability of Malagasy rainfall through applied climatology
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Keywords
Malagasy Climate Variability