the number of heatwaves per season is forecasted to increase from 60 days in south
of Southern America to 120 days in Eastern Africa, the Amazon Basin, and
Western Africa. Under such a scenario, heatwave conditions would become the new
normal. For a global 1 °C increase in mean warming, a regional divergence prevails, with lower latitude regions showing faster increases in heatwave days. Lower
levels of global warming will be reflected in minimal extremely intense heat events.
The regional variation of the number of seasonal heatwaves and global temperature increase is not linear. The number of events decreases with mean temperature increases of 1.5–2 °C in Eastern Africa and of 3 °C in Western Africa and
Sahara regions. For many other regions considered, the predominant rate of
increase of heatwave events peaks at about 3 °C of mean global warming. Some
regions such as Southeast and South Asia and Mediterranean Basin show a peak at
4.5 °C mean global warming. Large increases in heatwave days result in
no-lagging, long continuous events. The longest events are located over tropical
areas, such as Sahara, the Amazon Basin, Central America, and Eastern Africa. In
these regions, under a 5 ºC mean global warming, heatwaves could last 80 days but
under a scenario of 2–3 °C, the duration of heatwaves would be substantially
shorter of about 20 to 40–50 days, respectively.
The median temperature regional peak heatwave increases linearly with global
warming, with the largest increase occurring in the Mediterranean Basin, where
heating intensity could be 9 °C under a mean global heating scenario of 5 °C in
2100, compared with pre-industrial values. Under mean global heating of 2.5 °C,
heatwaves could peak between an additional 2.5 °C in Australia and Southern
South America and 5 °C in the Mediterranean Basin and Central Asia. This increase
is significantly higher when compared with the mean global 1.5 °C scenario, where
heatwave additional peaking range is between 2 °C in East Asia and Southern
America and 3 °C in the Mediterranean Basin and Central Asia.
Regional median return periods of heatwaves are forecasted to decrease at a
non-linear rate with an increasing mean global threshold. At a 4 °C global warming,
in almost all regions, a yearly intense heatwave could occur, compared with 1
equivalent event every 30 years, between 1861 and 1890. The return times are
substantially different under 1.5 and 2.5 °C scenarios across regions. In some
regions such as Tibet, central North America, eastern North America, and East
Asia, a threefold higher return time can occur at scenarios of 1.5 and 2.5 °C mean
global warming. The estimated return times were also about twofold higher in
regions such as Greenland, Northern Europe, Australia, Central America, North
Asia, and South Asia. In the Mediterranean Basin, it is about 1.5-fold higher.
The relationships detected by Perkins-Kirkpatrick and Gibson (2017), between
regional heatwave characteristics and global mean warming, are model-dependent.
For example, the overall spread of heatwave days per °C among the 27 models can
be as large as 40. On the other hand, the lengthening of the longest event can also
spread among the models across 30 days, under equal conditions. Tropical regions,
very sensitive to average global temperature increases, displayed the highest differences among models. The spreads are reduced outside tropical regions, with
heatwave days changing by 8–20 days, event number by 1–2.5 days, and the
8.4 Occurrence of Extreme Events
285
of Southern America to 120 days in Eastern Africa, the Amazon Basin, and
Western Africa. Under such a scenario, heatwave conditions would become the new
normal. For a global 1 °C increase in mean warming, a regional divergence prevails, with lower latitude regions showing faster increases in heatwave days. Lower
levels of global warming will be reflected in minimal extremely intense heat events.
The regional variation of the number of seasonal heatwaves and global temperature increase is not linear. The number of events decreases with mean temperature increases of 1.5–2 °C in Eastern Africa and of 3 °C in Western Africa and
Sahara regions. For many other regions considered, the predominant rate of
increase of heatwave events peaks at about 3 °C of mean global warming. Some
regions such as Southeast and South Asia and Mediterranean Basin show a peak at
4.5 °C mean global warming. Large increases in heatwave days result in
no-lagging, long continuous events. The longest events are located over tropical
areas, such as Sahara, the Amazon Basin, Central America, and Eastern Africa. In
these regions, under a 5 ºC mean global warming, heatwaves could last 80 days but
under a scenario of 2–3 °C, the duration of heatwaves would be substantially
shorter of about 20 to 40–50 days, respectively.
The median temperature regional peak heatwave increases linearly with global
warming, with the largest increase occurring in the Mediterranean Basin, where
heating intensity could be 9 °C under a mean global heating scenario of 5 °C in
2100, compared with pre-industrial values. Under mean global heating of 2.5 °C,
heatwaves could peak between an additional 2.5 °C in Australia and Southern
South America and 5 °C in the Mediterranean Basin and Central Asia. This increase
is significantly higher when compared with the mean global 1.5 °C scenario, where
heatwave additional peaking range is between 2 °C in East Asia and Southern
America and 3 °C in the Mediterranean Basin and Central Asia.
Regional median return periods of heatwaves are forecasted to decrease at a
non-linear rate with an increasing mean global threshold. At a 4 °C global warming,
in almost all regions, a yearly intense heatwave could occur, compared with 1
equivalent event every 30 years, between 1861 and 1890. The return times are
substantially different under 1.5 and 2.5 °C scenarios across regions. In some
regions such as Tibet, central North America, eastern North America, and East
Asia, a threefold higher return time can occur at scenarios of 1.5 and 2.5 °C mean
global warming. The estimated return times were also about twofold higher in
regions such as Greenland, Northern Europe, Australia, Central America, North
Asia, and South Asia. In the Mediterranean Basin, it is about 1.5-fold higher.
The relationships detected by Perkins-Kirkpatrick and Gibson (2017), between
regional heatwave characteristics and global mean warming, are model-dependent.
For example, the overall spread of heatwave days per °C among the 27 models can
be as large as 40. On the other hand, the lengthening of the longest event can also
spread among the models across 30 days, under equal conditions. Tropical regions,
very sensitive to average global temperature increases, displayed the highest differences among models. The spreads are reduced outside tropical regions, with
heatwave days changing by 8–20 days, event number by 1–2.5 days, and the
8.4 Occurrence of Extreme Events
285