Heat wave occurrences over Senegal during spring: Regionalization and synoptic patterns

Abstract

Based on 12 Senegalese stations of the Global Summary of the Day (GSOD) database (1979–2014), heat waves (HW) are defined for each station in spring (March–April–May, the hottest season in Senegal) as the daily maximum temperature (Tx), minimum temperature (Tn), or average apparent temperature of the day (AT), exceeding the corresponding 95% mobile percentile for at least three consecutive days. A hierarchical cluster analysis used to regionalize HW in these 12 stations is applied to simultaneous occurrences of daily temperature peaks over their 95% mobile percentiles. Three homogeneous zones of four stations each are identified (Zone 1, Zone 2 and Zone 3), from west (Atlantic coastline) to east (inland Senegal). Atmospheric circulation associated with HW is assessed through composites of ERA‐Interim deseasonalized anomalies, with the start date of each HW in each zone used as a reference. The main pattern controlling the presence of HW in Senegal consists in positive pressure anomalies centred around the strait of Gibraltar, promoting easterly to northeasterly wind anomalies. This causes higher temperatures in the three zones of Senegal, and lower temperatures and drier air over the central Sahel. This pattern is opposite to that characteristic of HW in the central Sahel shown in previous studies. From Zone 1 to Zone 3, the temperature and moisture patterns are shifted to the east while pressure anomalies weaken drastically. Night‐time Tn‐HW are characterized by higher water vapour contents than daytime Tx‐HW, corroborating and complementing previous studies over the Sahel. These HW patterns are close to the canonical mode of intra‐seasonal atmospheric variability over Senegal.

Characteristics and thermodynamics of Sahelian heatwaves analysed using various thermal indices

“…In terms of underlying thermodynamic processes, despite differences of the sampling bases, comparisons of the findings of this paper with that of previous publications can still be made. Most notably our findings agree with Guichard (2014), Oueslati et al (2017) and Sambou et al (2020) on the leading role of greenhouse effect of moisture during Sahelian nighttime heatwaves. It should be noted that this process is not specific to the Sahel but is also observed during nighttime heatwaves over other tropical regions (e.g Oppermann et al 2017;Chen et al 2019).…”

Heat waves in spring from Senegal to Sahel: Evolution under climate change

“…Senegal is considered as a second domain of interest, useful to assess the oceanic influence on temperature extremes. Finally, the three zones within Senegal that have been defined in Sambou et al (2020) are retained (Figure 1).…”

“…A HW is defined in Sambou et al (2020) as a sequence of at least three consecutive days above the 95th temperature percentile (p95). The percentile values are calculated day by day over March-May using a 29-day long moving window in order to take into account the marked seasonal temperature evolution in spring.…”

“…Under current climate conditions, Sambou et al (2020) investigated the synoptic atmospheric pattern associated with HWs over Senegal during spring (March-May) 1979-2014. The detection of 'hot' days has been carried out on 12 Senegalese weather stations (see Figure 1 for their location).…”

“…In this paper, we pursue this analysis, by assessing how a HW may evolve over the Sahel and over Senegal in the coming decades. To that end, we develop a multiscale approach for HWs identification in different RCP (Representative Concentration Pathways) scenarios over three nested domains, a 'Sahel' domain, Senegal, and the three zones identified by Sambou et al (2020) within Senegal. Special attention is given here to the long-term changes in the intrinsic properties of HWs, namely, their durations, intensities and frequencies.…”