What is a heat wave?
A heatwave is the occurrence of abnormally high temperatures for several consecutive days. It can be caused by dry, clear weather, or by persistent winds from hot regions such as the Sahara. These extreme weather events pose a threat to health, biodiversity and the Moroccan economy. These events are expected to be more frequent and more intense in the century to come.
Projections for 2050 in Morocco
Today, Morocco's average 20 days a year heatwaves. Their frequency and intensity are already multiplying, with the heatwave in May 2022 in several of the Kingdom's provinces. For a warming scenario of 2.5°C in 2050 - in line with current projections - it is estimated that this number would rise to 60 days per year. For a warming scenario of 4.5°C in 2050 - continuing the increase in greenhouse gas emissions - this would rise to 100 days per year.
Visualization of the number of heat wave days per year for a warming of 2.5°C (current projections) and 4.5°C (increase in emissions) in 2050.
Vulnerability and health risks
Among the populations most vulnerable to heat waves are the homeless, people in poor health, workers overexposed to heat, infants and the elderly. If we don't decide to drastically reduce our greenhouse gas emissions, situations of thermal discomfort will become the norm for all these populations by the middle of the century. We are projecting a increased risk of hyperthermia caused by extreme thermal discomfort in summer (thermal discomfort = temperatures felt above 32°C) by the end of the century.
As well as creating discomfort, heatwaves also present health risks. The human body needs to remain at its normal temperature (around 37°C). During a heatwave, it therefore starts to exert itself to regain this temperature. If this effort is too great, it can have cardiovascular, respiratory, digestive and cognitive effects. Thus, it is estimated that the mortality risk for the over-65s in 2050 under conditions of extreme heat would be multiplied by a factor of between 2 and 5 for a warming of 2.5°C. For a warming of 4.5°C in 2050, this factor rises from 3 to 8. And it's to be expected that those in a position to help the most vulnerable will also be in trouble.
Vulnerable populations and different levels of risk depending on heat intensity. Source : Waves and heat and health, Mathilde Pascal 2021
Urban island effect
The effects of heat waves are amplified in urban environments. The lack of vegetation, the high level of human activity and the heat trapped by urban materials all contribute to the intensity of heat waves. This effect is known as urban heat island effect. Conversely, transpiration from plants in vegetated areas helps to cool the atmosphere and compensate for the heat. As a result, the night-time temperature difference between a city and the countryside can reach 10°C in summer during a heatwave.
Illustration of factors contributing to the urban island effect, Source: Paris Climate Agency
The lack of vegetation in the kingdom's arid zones also has a positive impact on the environment. amplifying effect. As in urban environments, the absence of vegetation due to dry soils reduces the cooling effect that could have been achieved by evaporation and plant transpiration.
Economic consequences
Heat waves also have economic consequences. It is projected, for example, that for a warming scenario of 4.5°C in 2050, thermal discomfort would lead to an additional reduction in work capacity of 20% in 2050 and 40% in 2100 during the hottest months of the year.
When they become too long and intense, heat waves also represent a threat to agricultural crops and livestock. Prolonged exposure to abnormally high temperatures - coupled with a context of drought - leads to the loss or malformation of hectares of cereal crops, as was the case at spring 2022. Heat waves are also the cause of an increase in excess livestock mortality, as demonstrated by the heatwave in the summer of 2003, which resulted in the loss of almost 5 million poultry.
Heatwave episodes, which will become more intense and more frequent in the coming years, therefore represent a direct loss of yield for farmers and a threat to the kingdom's food security.
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Article by Shahine Bouabid