Seasonal variability of rainfall and thunderstorm in Guinea over the period 1981 to 2010

Republic of Guinea is one of the West African countries which share form a border with the southern part of the Sahel. It is located in the tropical area where the convective systems activities are intense with strong rainfall. Our results on Standardized Precipitation Index are coherent with the Sahel drought during the 1970s, and a recovery period of rainfall since the last years. The Standardized Thunderstorms Index shows positive anomalies (1981-1997) corresponding to the dry period of rainfall, while a negative anomalies is shown (1998-2010) for the wet period. This study highlights the relationship between thunderstorms and rainfall amounts in Guinea in the context of climate variability. Indeed, by categorizing the rainfall in two groups respectively weak and heavy, we calculated their correlations with thunderstorms. We found significant correlations between weak rainfall and thunderstorms. To appreciate the findings with the standardized anomalies of precipitation and thunderstorms, we also performed Rotations of Empirical Orthogonal Function and Principal Component Analysis to identify the coherent mode of the interannual variability of these parameters. We found that the first mode is the best Empirical Orthogonal Function which is coherent with is the results shown by the Standardized Index of Precipitation and Thunderstorms. To check the significance of each Empirical Orthogonal Function mode, we use the North's rule of thumb for estimating the sampling errors. It was noticed that no modes was concerned by sampling errors. And then, the rainfall seasonal cycle shows a unimodal rainfall regime, while the thunderstorms' one indicates a bimodal cycle. Our study could improve knowledge about rainfall amounts and thunderstorms variability, especially in climatic variability context.