Global climate projections suggest a significant intensification of summer heat extremes in the Middle East and North Africa (MENA). To assess regional impacts, and underpin mitigation and adaptation measures, robust information is required from climate downscaling studies, which has been lacking for the region. Here, we project future hot spells by using the Heat Wave Magnitude Index and a comprehensive ensemble of regional climate projections for MENA. Our results, for a business-as-usual pathway, indicate that in the second half of this century unprecedented super- and ultra-extreme heatwave conditions will emerge. These events involve excessively high temperatures (up to 56 °C and higher) and will be of extended duration (several weeks), being potentially life-threatening for humans. By the end of the century, about half of the MENA population (approximately 600 million) could be exposed to annually recurring super- and ultra-extreme heatwaves. It is expected that the vast majority of the exposed population (>90%) will live in urban centers, who would need to cope with these societally disruptive weather conditions.

The objective of this analysis is to provide an up-to-date observation-based assessment of the evolution of temperature extremes in the Middle East–North Africa (MENA) region and evaluate the performance of global climate model simulations of the past four decades. A list of indices of temperature extremes, based on absolute level, threshold, percentile and duration is used, as defined by the Expert Team on Climate Change Detection and Indices (ETCCDI). We use daily near-surface air temperature (Tmax and Tmin) to derive the indices of extremes for the period 1980–2018 from: (i) re-analyses (ERA-Interim, MERRA-2) and gridded observational data (Berkeley Earth) and (ii) 18 CMIP5 model results combining historical (1950–2005) and scenario runs (2006–2018 under RCP 2.6, RCP 4.5 and RCP 8.5). The CMIP5 results show domain-wide strong, statistically significant warming, while the observation based ones are more spatially variable. The CMIP5 models capture the climatology of the hottest areas in the western parts of northern Africa and the Gulf region with the thewarmest day (TXx) > 46 ∘C and warmest night (TNx) > 33 ∘C. For these indices, the observed trends are about 0.3–0.4 ∘C/decade while they are 0.1–0.2 ∘C/decade stronger in the CMIP5 results. Overall, the modeled climate warming up to 2018, as reflected in the indices of temperature extremes is confirmed by re-analysis and observational data.

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This study analyzes projected heat extremes over the Middle-East–North Africa (MENA) region until the end of the twenty-first century with a number of temperature indices based on absolute values and thresholds to describe hot conditions. We use model projected daily near-surface air (2-m) temperature ($$T_\mathrm{{max}}$$ T max and $$T_\mathrm{{min}}$$ T min ) to derive the indices for the period 1980–2100. The data were taken from 18 CMIP5 models combining historical (1980–2005) and scenario runs (2006–2100 under RCP2.6, RCP4.5, and RCP8.5 pathways). Results show a domain-wide projected warming for all emission scenarios. Our findings for a business-as-usual pathway indicate excessive warming of more than 8 $$^\circ $$ ∘ C in the northern part of the domain (south Europe) for the annual warmest day (TXx) and night (TNx). In the hottest parts of the domain record high temperatures reached 50 $$^\circ $$ ∘ C in the recent past, which could increase to at least 56 $$^\circ $$ ∘ C by the end of the century, while temperatures over 50 $$^\circ $$ ∘ C are expected to occur in a large part of the MENA region. A significant increase is projected in the number of hot days (TX $$>40^\circ $$ > 40 ∘ C) and nights (TN $$>30 ^\circ $$ > 30 ∘ C) all over the region. For the period of 2071–2100 excessive hot days and nights will become the normal during summer in large parts of the MENA with some locations expected to exceed 180 and 100 days, respectively. Calculations of the corresponding heat index suggest that several areas across the MENA region may reach temperature levels critical for human survival.

<p>A correct representation of the planetary boundary layer (PBL) is critical to achieve realistic simulations, especially regarding surface variables for regional climate simulations. In this study we examine the sensitivity of the performance of the Weather Research and Forecast (WRF) model to the use of three widely used PBL schemes with emphasis on heat extremes. This study aims (i) to explore the differences among the WRF simulated air temperature and heat extremes resulting from the choice of PBL schemes, (ii) to investigate the physical causes of model biases via the analysis of different variables and, finally, (iii) to reveal the most suitable scheme for application in the Middle-East - North Africa (MENA) domain. The schemes under evaluation are the Mellor–Yamada–Janjic (MYJ), Yonsei University (YSU), and the asymmetric convective model, version 2 (ACM2). We performed 11-year (2000-2010) simulations over the MENA region at 24km resolution. The simulations have been compared with the ERA5 reanalyses for several variables, including maximum and minimum 2-meter air temperature and indices of extremes. Results indicate that model biases strongly vary according to geographic area, with simulations showing good performance in some regions and substantial biases in others. Analysis of different variables like PBL height, moisture and heat fluxes show that differences among the schemes can be linked to differences in vertical mixing strength and entrainment of air from above the PBL.</p>