Business-as-usual will lead to super and ultra-extreme heatwaves in the Middle East and North Africa

Human-induced global warming is expected to significantly impact the Mediterranean region, particularly the MENA region, throughout the 21st century. This warming trend, coupled with less certain changes in precipitation, will lead to a disproportionate increase in summer temperatures. Consequently, heatwaves are projected to increase in frequency, intensity, and duration. Observed trends in heat extremes already corroborate model simulations showing a transition to warmer conditions since the 1980s. The intensification of heatwaves in the already harsh MENA environment poses severe risks to human health, agriculture, water resources, energy systems, and overall socioeconomic stability. Heat stress can cause substantial labor productivity loss and may even be linked to conflict and migration. Livestock, particularly camels, cattle, and goats, will also be negatively affected. Impacts on human health include heart cramps, heat syncope, heat exhaustion, and heatstroke, especially among vulnerable populations. In some parts of the Middle East, especially near the Arabian Gulf, the combined effects of high temperature and humidity are predicted to exceed human adaptability thresholds. Large gatherings, such as the Hajj, are also particularly vulnerable. The region's high and increasing urbanization, concentrated in large metropolitan areas, will exacerbate the problem through the urban heat island (UHI) effect. Existing literature mostly relies on coarse-resolution global simulations or regional modeling that inadequately represents MENA's unique climate features. This study addresses this gap by utilizing a comprehensive MENA-focused climate downscaling initiative to provide high-quality regional information.

The paper reviews existing literature on heatwave projections in the MENA region, noting that most studies are based on global simulations at relatively coarse resolution or regional modeling that doesn't fully capture the region's complexities. It highlights the lack of high-quality regional information and the need for a MENA-focused climate downscaling initiative. The review includes research on the impacts of heatwaves on various sectors in the region, such as human health, agriculture, water resources, and energy. Previous studies are referenced to demonstrate the significance of the warming trends in MENA and the need for improved modeling.

The study analyzed a multi-model ensemble of ten MENA-CORDEX simulations, combining six global earth system models and four regional climate models, following CORDEX guidelines. Future climate projections (2006–2100) were generated for the Representative Concentration Pathway (RCP) 8.5 (business-as-usual) scenario, with a comparison also conducted for RCP 4.5. The horizontal resolution was 0.44° (~50 km). The warm season was defined as May to September. Simulated mean values and absolute maxima were compared with gridded observations from the Climate Research Unit (CRU) and Berkeley Earth datasets. A percentage-based definition of heatwaves was used, defining a heatwave as at least three consecutive days with a maximum temperature above the 95th percentile of daily maxima (31-day window) from the 1981–2010 reference period. The daily Heat Wave Magnitude Index (HWMI) was used to assess heatwave intensity, combining duration and temperature anomalies. Population exposure was calculated by combining future HWMI estimates with gridded population projections from the Shared Socioeconomic Pathways (SSPs), specifically SSP5. The 0.1° population data was aggregated and resampled to match the MENA-CORDEX grid. Linear interpolation was used to create annual population numbers for the years 2010–2100.

The study's key findings indicate a significant intensification of heatwaves in the MENA region under the RCP8.5 scenario. By the end of the century, the entire region is projected to experience at least one moderate, severe, or very extreme heatwave annually. Unprecedented super-extreme and ultra-extreme heatwaves will become commonplace, affecting about 60% of the region annually. These events will be characterized by exceptionally high temperatures (exceeding 56°C in some areas), extended durations (several weeks), and high frequency. Approximately 600 million people (about half the MENA population) could be exposed to annually recurring super- and ultra-extreme heatwaves by the end of the century, with over 90% of this population residing in urban centers. The average duration of heatwaves is projected to increase significantly, exceeding ten days in many locations and lasting more than a month in some hotspots. The amplitude of heatwaves will also increase, with maximum temperatures potentially exceeding 56°C in some regions. The frequency of severe, extreme, and very extreme heatwaves will increase dramatically, particularly in inland regions. Model limitations and the exclusion of the urban heat island effect are noted. Comparisons with the RCP4.5 scenario indicate that even under less pessimistic conditions, severe impacts are expected.

The findings strongly suggest that the MENA region will face an unprecedented increase in the intensity, duration, frequency, and spatial extent of heatwaves under a business-as-usual scenario. The projected extreme heat will severely threaten human health, agriculture, and biodiversity. The results largely agree with other high-resolution studies for the Mediterranean part of the domain. The strong warming is attributed to the intensification of the greenhouse effect due to anthropogenic emissions and land-use changes, along with amplifying feedbacks such as land-atmosphere interactions and expanding soil moisture deficits. The conservative estimate of exceeding 56°C in some areas highlights the critical need for mitigation and adaptation strategies. The UHI effect, not fully considered in the model due to resolution limitations, is expected to further exacerbate temperatures in urban areas. The comparison between RCP8.5 and RCP4.5 scenarios underscores the need for urgent action, even under less extreme emission scenarios.

The study concludes that the MENA region will experience an unprecedented increase in extreme heatwave events unless substantial mitigation measures are implemented. The projected super-extreme and ultra-extreme heatwaves will have severe societal and environmental consequences. Further research should focus on refining the modeling of urban heat island effects and exploring mitigation and adaptation strategies specific to the MENA region. The findings emphasize the urgent need for MENA countries to prioritize preparations for exceedingly hot summers.

The study acknowledges limitations related to the spatial resolution of the climate models used. The urban heat island effect was not explicitly considered, potentially underestimating the severity of heatwaves in urban areas. The limited number of simulations for less pessimistic scenarios (e.g., RCP2.6) restricts the analysis of these conditions. While the models reasonably captured the mean spatial patterns of warm-season temperature, local discrepancies and biases from observations were present.