Variability of convective rainfall in the austral summer season over central Madagascar is studied using an area-rainfall index, local radiosonde data, and gridded information on outgoing longwave radiation (OLR), sea-surface temperature, and tropospheric winds. Seasonal rainfall patterns are influenced by topography, monsoon and trade wind circulations, and tropical cyclone events. The Inter Tropical Convergence Zone overlies the north-west coast, where summer rainfall averages 47 cm month-'. Climatic conditions that affect convective rainfall at interannual time-scales are studied through spatial lag correlation analysis. Sea-surface temperature is weakly correlated with rainfall departures, with positive values in the central Indian Ocean reaching +0.41 at lags -4 and 0 months. Strongest positive correlations (+0.45) gradually shift to the central South Atlantic Ocean at lag 0 and +2 months. Wind correlations imply that increased upper level tropical easterly flow overlying enhanced low-level north-west monsoon flow favours above normal rainfall. Regional teleconnection patterns identified by rainfall-OLR correlations are remarkably similar to those for Quasi-biennial oscillation (QBOWLR correlations, suggesting that up to one-third of the interannual convective variance can be explained by the phase of the QBO.

Outputs from 25 regional climate models within the coordinated regional downscaling experiments—Africa are used to assess the impacts of the 1.5°C and 2°C global warming levels (GWLs) over Madagascar. A robust increase in the annual mean temperature ranging from 0.9°C to 1.2°C (1.3°C–1.8°C) is projected in the 1.5°C (2°C) GWL. The west and southwestern parts of the island display the highest rise in temperature. On the other hand, the changes in rainfall signals depend on the location, the months within the rain season and the warming level with the models showing a large uncertainty in the signal of changes. During early summer, the west and southwest regions exhibit an increase in total rainfall accompanied with more wet spell days and excessive amounts of extreme rainfall. In contrast, the east and the north are characterized by a deficit in total rainfall and wet spell days while the maximum number of dry spells increase. The change signals are more pronounced in the 2°C GWL. From January to April, an overall increase in total and extreme rainfall is projected over the island. The two warming levels agree on the delay in the rainfall onset and shortening of the rainfall season with the 2°C GWL depicting more modest changes in the west and southern parts of the country compared to that of 1.5 °C GWL. These results have important implications not only for the development of the country but also for the endemic biodiversity which is already suffering from the impacts of climate change.