Co-occurrence of extreme ozone and heat waves in two cities from Morocco

Abstract

Temperature is the first meteorological factor to be directly involved in leading ozone (O3) extreme events. Generally, upward temperatures increase the probability of having exceedance in ozone adopted thresholds. In the global climate change context more frequent and/or persistent heat waves and extreme ozone (O3) episodes are likely to occur during in coming decades and a key question is about the coincidence and co-occurrence of these extremes. In this paper, using 7 years of surface temperature and air quality observations over two cities from Morocco (Casablanca and Marrakech) and implementing a percentile thresholding approach, we show that the extremes in temperature and ozone (O3) cluster together in many cases and that the outbreak of ozone events generally match the first or second days of heat waves. This co-occurrence of extreme episodes is highly impacted by humidity and may be overlapping large-scale episodes.

Concurrent Heat Waves and Extreme Ozone (O3) Episodes: Combined Atmospheric Patterns and Impact on Human Health

“…Extreme events may be partly explained by these averages. This statement is in complete agreement with many other climatological and air pollution studies over the area [20,33,43,51].…”

“…This spotlights the role of the geographical location of the cities and the influence of meteorological parameters on events' occurrence. This influence was highlighted in many previous studies as well [1,6,7,[9][10][11]15,16,19,20,52]. For example, the study by Chen et al concluded that soaring ozone concentrations across China in 2017 could be mainly attributed to the notable change of meteorological conditions in 2017, characterized with rising temperature and sunshine duration and decreasing relative humidity [52].…”

“…The thresholding method is widely employed and recommended by the STARDEX (STAtistical and Regional dynamical Downscaling of EXtremes for European regions; https: //crudata.uea.ac.uk/projects/stardex/, access on 14 December 2021) and the ETCCDI (Expert Team on Climate Change Detection and Indices) projects (Brown et al, 2010). Many studies in Morocco have used this approach [20,22,33].…”

“…Morocco is located in northwest Africa [ 20 ]. It is bordered by the Atlantic Ocean to the west, Algeria to the east, Mauritania to the south, and the Mediterranean Sea to the north ( Figure 2 ).…”

“…In Africa, the simultaneous appearance of heat waves and ozone episodes and their relationship with the large-scale atmospheric circulation is underconsidered by the scientific literature in the region. Khomsi et al explored the concurrence of extreme O 3 and hot events, in two urban cities from Morocco, during the extended summer (April–September) between 2009 and 2016 [ 20 ]. Authors reported that 33% of hot events matched O 3 episodes in the coastal city of Casablanca, as compared to 70% in the inland city of Marrakech.…”