Dynamic of heat waves in the sahel of 1982-2014: study the potential role of precipitation and vegetation

This report aims to make a state of the art of the evolution of heat waves during the period 1982 to 2014 in the Sahel and to try to establish a link between heat waves and precipitation as well as Normalized Difference Vegetation Index (NDVI). This will allow a better predictability of future changes in heat waves, the only way to minimize the damage because the models predict that warming will continue even beyond the 21st century. Estimation of heat waves was made on the basis of the heat index that combines air temperature and relative humidity to get a value which determines the temperature felt by the skin. The threshold is set at the 90th percentile of the heat index for a period of at least 3 days together with a minimal spatial extension. Heat waves appear seasonally, with a maximum during the month April-May-June (WAN) and they had a high inter-annual variability during the period 1982-2014. The years 1998 and 2010 have been severe heat waves extensions while those of 1982, 1984 and 1985 recorded low. The study on the severity of episodes of summer heat waves carried on the threshold of the intensity of the heat index and duration. It appears that the years 1998, 2001 and 2010 were severe. The correlation between heat waves in spring and summer precipitation in the same year give a correlation coefficient r = 0.30. This result was impacted by the effect of El Nino Southern Pacific (Multivariate ENSO Index (MEI)) and lowered r=0.10. The MEI is correlated with heat waves of spring and summer precipitation for respective values of correlation coefficient r = -0.20 and r = -0.17. Then the correlation coefficient of the precipitation of the year (n-1) and the heat waves of the year (n) was r = 0.29. This correlation value is found to be very strong by eliminating the abnormally hot years (1998 and 2010), with a coefficient r = 0.56.The studies also try to link heat waves and the last year normalized difference vegetation index (NDVI) a correlation coefficient equal to r = 0.28 was found and correlation between NDVI and summer precipitation gave r = 0.67.