This study evaluated six hot extremes, including MaxTmax, MeanTmax, 95Tmax, Tmax95p, D40Tmax, D45Tmax, and four cold extremes, MinTmin, MeanTmin, 05Tmin and Tmin05p. The characteristics of these hot and cold extremes were spatially analyzed for the historical and projected changes for the early and late future periods (2020–2059, 2060–2099, respectively), considering three SSPs, as described in the next sub-sections. The performance of the selected GCMs in simulating ERA5 extremes before and after bias correction, based on KGE, is presented in Fig. 2. All GCMs showed an improvement in KGE in simulating extremes. However, the improvement was less for MinTmin and Tmin05p.
Figure 3 represents Taylor diagrams for each extreme before and after bias correction of GCMs, and the MME mean of the bias-corrected GCMs. The x-axis features a hollow circle with reference data (i.e., ERA5). GCMs before and after bias correction are represented using colored circles. The best performing model is shown by the model indicator closest to the hollow circle. All extremes indicated better performance after bias correction. The MME of the bias-corrected GCMs was the nearest to the hollow circle for most of the extremes.
4.1. Hot Extreme
The spatial distributions of MaxTmax for the reference period and two futures over Egypt are presented in Fig. 4. The highest MaxTmax (47.2 ℃) was detected in the southeast, while the lowest (32.3℃) was in the northern and eastern parts of the study area. Most parts of the country would experience a MaxTmax of more than 45.0℃. The areal distribution of projected changes in the MaxTmax was almost alike, considering all SSPs scenarios. However, the increase in MaxTmax was greater under worst-case scenarios and for the late future compared to the early future. For example, SSP1-2.6 showed a positive change from nearly 0.0℃ in the early future to 3.0℃ in the late future near the border between Egypt and Sudan. An increase in MaxTmax by 1.3 to 3.8℃ was projected over most of Egypt for SSP2-4.5 in the late future. The projected increase was 0.5 to 2.3℃ in the early future in the same region. SSP5-8.5 showed the highest MaxTmax increase, 5.4℃, over most of the country in the late future.
The geographical distributions of MeanTmax for the reference period and the two futures over the study area are presented in Fig. 5. The highest value of MeanTmax (33.9℃) for the historical period was observed in the southeast, while the lowest (22.0℃) was in the coastal north. Most parts of the country showed a MeanTmax of 27.5 to 30.0℃. The spatial patterns of projected changes for all SSPs were almost similar. However, the higher rate of increase in MeanTmax was for worst-case scenarios and the late future. The change in MeanTmax was low over the country for the two futures employing SSP1-2.6. In contrast, SSP2-4.5 projected an increase in MeanTmax from 1.5℃ in the early future to 2.3℃ in the late future. The projection showed a relatively higher increase when using SSP5-8.5, from 1.7℃ in the early future to 3.7℃ in the late future, except for a thin patch (2.1℃) in the vicinity of the Red Sea.
Figure 6 indicates the areal distribution of 95Tmax for the historical period and two futures. The country has experienced a 95Tmax of 28.8 to 42.8℃, but most areas showed a temperature ranging between 35 and 42.8℃. The projected changes considering SSP1-2.6 for the two futures showed similar spatial distribution of change in 95Tmax at 1.5 to 2.0℃. The increase was higher for higher SSPs and in the late future. SSP2-4.5 presented an increase in 95Tmax by 1.5℃ in the early future and 2.5℃ in the late future. SSP5-8.5 showed a maximum change of 2.1℃ in the early future and 4.8℃ in the late future. Figure S-3 represents the spatial pattern of Tmax95p for the historical period and the two futures. The historical simulation showed that Tmax95p ranges between 5.25 and 5.75%, with the highest values in the southeast region. The spatial distributions in the projected changes in Tmax95p were more or less similar in the two futures and three SSPs. Percentage in the number of hot days showed a higher decrease in the near future than in the far future. The increase was more in the central area for all SSPs in the far future.
The spatial patterns of D40Tmax for the reference period and two futures are visualized in Fig. 7. The country experiences D40Tmax from 1 day in the north to 84 days in the south in the historical period. South and southeast Egypt witnessed 45–84 days of temperature above 40℃, while it is 5 to 30 days in the west and southwest. The projected change showed a gradual increase in the spatial distribution of D40Tmax, with increased variation for the late future compared to the early future and higher SSPs. SSP1-2.6 projection showed that the south was likely to experience 20–40 days D40Tmax, while the areal extent of this change was greater for the late future in the south. SSP2-4.5 presented an increase in D40Tmax by 30–40 days in the early future and by 50–70 days in the late future. The highest increase (70–95 days) was projected in most parts of the country for the late future compared to the early future (10–50 days). The spatial distributions of D45Tmax are presented in Figure S-1. Smaller areas in the south and southeast of the country experience 1 or 2 days of temperatures above 45℃ in the reference period, while most regions never witness any temperatures above 45℃. The projection showed an increase by 10 days for most areas except the small part in the south, especially in the late future. However, the number of days increased for higher SSPs and in the late future. The highest increase (52 days) in D45Tmax was projected in a small patch in the south when using SSP5-8.5, while the lowest increase (7 days) was with SSP1-2.6 over the same area.
4.2. Cold Extreme
The areal distributions of annual MinTmin for the reference period and the projected changes are shown in Fig. 8. The lowest MinTmin was 0.0℃ for the historical period in the northeast and southwest, while the highest MinTmin was 14.1℃ in the country's far southeast. Most parts of the country showed MinTmin of 2.0℃. The changes in MinTmin were similar to hot extremes. The larger increase was in the late future compared to the early future for higher SSPs. The increase for SSP1-2.6 was 2.95℃ in the south, while it was 5.0℃ for SSP5-8.5 in the far future. All SSPs show a similar spatial distribution of MinTmin in the early future except for a thin path which was relatively higher (2.7℃) along the southern borders. However, the geographical distributions of MeanTmin for the historical period and the projected changes are visualized in Figure S-2. Like other indices, the positive change in MeanTmin was higher in the late future compared to the early future when using higher SSPs. However, similar spatial distributions of MeanTmin were for SSP1-2.6 in the two futures. Most of the country showed a MeanTmin of 2.7℃ in the late future for SSP2-4.5, while it was 4.3℃ for SSP5-8.5.
The spatial distributions of 05Tmin for the reference period and the projections are presented in Fig. 9. The highest 05Tmin (19.0℃) was in the east, while the lowest 05Tmin (3.0℃) was in the west and northeast of the country. A relatively larger area experiences a 05Tmin from 0 to 7.5℃. A positive change of 05Tmin was projected for the late future compared to the early future, and a gradual increase was observed for higher SSPs. For example, the projected change in 05Tmin was 1.4℃ over most of the study area under SSP1-2.6 in the early future and 1.5℃ in the late future. Similarly, they were noticed to be 1.6℃ in the early future and 3.6℃ in the late future under SSP5-8.5. Besides, Figure S-4 indicates the spatial pattern of Tmin05p for the historical period and the two futures. The historical simulation shows Tmin05p ranges between 5.25 and 5.75%, with the highest value in the southeast. The spatial distributions in the projected changes in Tmin05p were more or less similar in the two futures and for each SSP. The number of cold nights was projected to decrease for SSP1-2.6 by up to 0.1 and 0.13 in the near and far future, respectively. A greater increase in Tmin05p with 0.41 and 0.44% for SSP5-8.5 near and far future, respectively.