Malagasy Climate Variability, Characteristics, Modes, Mechanisms, Modelling, Teleconnection and Prediction

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Addis Ababa University


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 9 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 10 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



Malagasy Climate Variability