Oceanic influences on Sahelian extreme spring temperatures: insights from CMIP6 numerical experiments

Abstract:

Numerous studies have emphasized the importance of sea surface temperature (SST) on monsoonal Sahelian precipitation, from interannual to multidecadal and climatic time scales (e.g. Giannini et al. 2003). From a climate perspective, temperatures have greatly increased in the Sahel in the past decades, especially during the very hot months prior to the monsoon season, in April-May (e.g. Guichard et al. 2009, Guichard et al. 2017, Barbier et al. 2018).

In this study, we successively assess:

(i) the ability of CMIP6 models to accurately simulate Sahelian temperatures and whether they improved compared to those of CMIP5 models using ‘historical’ runs together with several observational datasets;

(ii) the sensitivity of April-May temperatures to SST by comparing ‘historical’ and Global Monsoons Model Intercomparison Project (GMMIP) ‘amip-hist’ runs over the period 1950-present (SST derived from observation are prescribed over the whole period).

Beyond large (several K) persisting errors affecting the simulation of Sahelian temperatures from CMIP5 to CMIP6, which will be illustrated and discussed, we find that the temperature climatic trends as well as the smaller time scales of variability are both better simulated in amip-hist compared to historical CMIP6 runs when focussing on the hottest period of the year. An analysis of associated changes in the atmospheric dynamics and thermodynamics helps the interpretation of these results.

Barbier J. et al., 2018: Detection of intraseasonal large-scale heat waves: Characteristics and historical trends during the Sahelian Spring. J. Climate. doi: 10.1175/JCLI-D-17-0244.1

Giannini A. et al., 2003: Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science, 302(5647), 1027-1030.

Guichard F. et al., 2009: Surface thermodynamics and radiative budget in the Sahelian Gourma: seasonal and diurnal cycles, J. Hydrology, 375, 161-177. doi: 10.1016/j.jhydrol.2008.09.007

Guichard F. et al., 2017: Climate warming observed in the Sahel since 1950. in 'Rural societies in the face of climatic and environmental changes in West Africa'. pp 23-42. AN13: 9782709924245 and 9782709924269.