RESUMO
The influence of intra-seasonal oscillations (ISO) on rainfall in Central Africa (CA) during the March-May (MAM) season is assessed using the National Oceanic and Atmospheric Administration Climate Prediction Center daily gridded rainfall data. ISO indices are defined using the time series analysis of the first two principal components resulting from the empirical orthogonal function, applied to daily filtered outgoing longwave radiation. Based on these indices, a total of 71 strong Intraseasonal Events (SIEs) and 66 weak Intraseasonal Events (WIEs) were selected using threshold method. The results show that SIEs are associated with enhanced rainfall conditions over almost all the study area, while WIEs provide a meridional dipole-like rainfall pattern, consisting of increasing precipitation in the western part and decreasing in the eastern part of CA. The relationship with Madden-Julian Oscillation (MJO) was also examined. The positive rainfall anomalies associated with MJO phases progress eastward and are modulated by the 850 and 200 hPa horizontal wind. The circulation, linked to geopotential height anomalies at lower layers, tends to strengthen (reduce) the convective activity over the region during extreme ISO events and for the MAM season throughout the study period. Uncentered pattern correlation was further used to assess the link between ISO and MJO phases during the MAM season and we found a correlation of 0.5 in precipitation anomalies between phases 1 and 2 of the MJO and the SIEs; - 0.4 and - 0.6 between phases 5 and 6 and the SIEs respectively, suggesting a strong relationship between ISO events and MJO.
RESUMO
Investigating the effects of the increased global warming through the lens of the Paris agreements would be of particular importance for Central African countries, which are already experiencing multiple socio-political and socio-economic constraints, but are also subject to severe natural hazards that interact to limit their adaptive capacity and thus increase their vulnerability to the adverse effects of climate change. This study explores changes in heat stress and the proportion of population at risk of discomfort over Central Africa, based on an ensemble-mean of high-resolution regional climate model simulations that cover a 30-year period, under 1.5, 2 and 3 °C Global Warming Levels (GWLs). The heat index was computed according to Rothfusz's equation, while the discomfort index was obtained from Thom's formula. The results show that throughout the year but with a predominance from March to August, the spatial extent of both heat and discomfort categories is projected to gradually increase according to the considered GWLs (nearly threefold for an increasing warming thresholds from 1.5 to 3 °C). As these heat conditions become more frequent, they lead to the emergence of days with potentially dangerous heat-related risks, where almost everyone feels discomfort due to heat stress. It thus appears that the majority of populations living in countries located along the Atlantic coast and in the northern and central part of the study area are likely to be more vulnerable to certain health problems, which could have repercussions on the socio-economic development of the sub-region through decreased workers' productivity and increased cooling degree days. Overall, these heat-related risks are more extended and more frequent when the GWL reaches 2 °C and above.