Spatio-temporal variability of rainfall and impacts on vegetation in Reunion Island

International audienceReunion Island is located in the southwest Indian Ocean with a diverse climatological context weakened by the consequences of global warming. The rugged terrain and the exposure to the east-west trade winds explain the abundance of microclimates on the island. The first objective of this study was to attempt to characterize the spatiotemporal variability of rainfall in La Reunion. The results of the identification of discontinuities in rainfall data series and drought indices highlight two different geographic situations. On the west, leeward coast, discontinuity in the rainfall series occurred between 1980 and 1989. It shows a significant decline in annual rainfall amounts (between 14 and 32%). On the east, windward coast, the discontinuities dates are variables (mainly between 1968 and 1972). There is only a small decrease or even an increase in the annual rainfall amounts. By observing the length of the rainy season, the imbalance between the windward coast’s climate and the leeward coast’s is extended. It is very short on the west coast since 2006 whereas the rainy season is difficult to separate from the dry season on the east coast because of the very important rainfall amounts throughout the year. As the areas of forest and grassland are falling steadily, a study of the impact of the rainfall spatiotemporal variability has to be done. Consequently, the second objective of this study was to measure of the co-variation between “rain” and “NDVI”. We used remote sensing methods using MODIS low-resolution images from 2000 to 2013. Results show that vegetative sets on the west of the island, which are often affected the water stress, respond well to rainfall changes. However, those on the east coast are less sensitive to a decrease or an increase in rainfall amounts. Nevertheless, the correlation coefficient has medium intensity with a maximum value ranging from 0,3 to 0,4. Yet, a multivariate analysis shows that the value of these coefficients is mainly due to the heterogeneous landscape of La Reunion