A climatology of air temperature extremes in the Mediterranean region for the 85-year period 1940-2024
Date Issued
September 29, 2025
Author(s)
Abstract
Extremely high/low temperatures along with the synoptic conditions leading to their appearance
are investigated for the Mediterranean region (55°N - 30°N, 0°E – 40°E) during the 85-year period
1940 - 2024. The data used are daily (04UTC and 12UTC) values of air temperature at 2m above
the Earth’s surface, 850hPa air temperature and 1000hPa and 500hPa geopotential heights, with
1°x1° spatial resolution, obtained from the ERA5 database. For 2m air temperature, the anomalies
are calculated as the differences between the initial values and the 85-year long-term averages for
the corresponding dates and are then used for the definition of Extreme High Temperature Days
(EHTDs) and Extreme Low Temperature Days (ELTDs). 3890 EHTDs and 4882 ELTDs are
defined. Statistically significant trends in the inter-annual variation of the number of these
extreme days show that EHTDs are evidently more frequent in recent years whereas ELTDs are
less frequent. A statistical analysis is applied on the data separately for the EHTDs and the
ELTDs, which includes the application of Principal Component Analysis (PCA) followed by
Cluster Analysis (CA), a procedure known as spectral clustering. As a result, 8 clusters are defined
for the EHTDs and 9 clusters are defined for the ELTDs, corresponding to different Mediterranean
sub-regions. The occurrence of EHTDs is mainly associated with intense solar heating, blocking
anticyclones and warm air advection from southern latitudes. On the contrary, ELTDs are
connected to intense radiative cooling of the Earth’s surface, cold air advection from northern
latitudes and Arctic outbreaks.
are investigated for the Mediterranean region (55°N - 30°N, 0°E – 40°E) during the 85-year period
1940 - 2024. The data used are daily (04UTC and 12UTC) values of air temperature at 2m above
the Earth’s surface, 850hPa air temperature and 1000hPa and 500hPa geopotential heights, with
1°x1° spatial resolution, obtained from the ERA5 database. For 2m air temperature, the anomalies
are calculated as the differences between the initial values and the 85-year long-term averages for
the corresponding dates and are then used for the definition of Extreme High Temperature Days
(EHTDs) and Extreme Low Temperature Days (ELTDs). 3890 EHTDs and 4882 ELTDs are
defined. Statistically significant trends in the inter-annual variation of the number of these
extreme days show that EHTDs are evidently more frequent in recent years whereas ELTDs are
less frequent. A statistical analysis is applied on the data separately for the EHTDs and the
ELTDs, which includes the application of Principal Component Analysis (PCA) followed by
Cluster Analysis (CA), a procedure known as spectral clustering. As a result, 8 clusters are defined
for the EHTDs and 9 clusters are defined for the ELTDs, corresponding to different Mediterranean
sub-regions. The occurrence of EHTDs is mainly associated with intense solar heating, blocking
anticyclones and warm air advection from southern latitudes. On the contrary, ELTDs are
connected to intense radiative cooling of the Earth’s surface, cold air advection from northern
latitudes and Arctic outbreaks.
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