The intensification of thermal extremes in west Africa

- Nocturnal and diurnal warming trends are identified over the Gulf of Guinea coastal region and the Sahel.
- Percentage of extreme warm nights and days are increasing since 1950.
- Maximal and mean duration of warm spells has increase over the Gulf of Guinea coastal regions; Only maximal duration of warm spells has increase over the Sahel
- Nocturnal trends in temperature indices are greater than the diurnal trends till the post-1980s period.
- These trends in extreme warm nights and days are consistent in the CMIP5 models.
- (An increase of extreme warm nights and days are expected over the 21st century.)

This study aims in filling the gap in understanding the relationship between trend and extreme in diurnal and nocturnal temperatures (Tx and Tn) over the Gulf of Guinea area and the Sahel. Time-evolution and trend of Tx and Tn anomalies, extreme temperatures and heat waves are examined using regional and station-based indices over the 1900-2012 and 1950-2012 periods respectively. In investigating extreme temperature anomalies and heat waves, a percentile method is used. At the regional and local scales, rising trends in Tx and Tn anomalies, which appear more pronounced over the past 60 years, are identified over the two regions. The trends are characterized by an intensification of: i) nocturnal/Tn warming over the second half of the 20th century; and ii) diurnal/Tx warming over the post-1980s. This is the same scheme with extreme warm days and warm nights. Finally annual number of diurnal and nocturnal heat waves has increase over the Gulf of Guinea coastal regions over the second half of the 20th century, and even more substantially over the post-1980s period. Although this trend in extreme warm days and nights is always overestimated in the simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), those models display rising trends whatever the scenario, which are likely to be more and more pronounced over the two regions in the next 50 years.