Extreme temperature in the Mediterranean basins

This study analyses daily maximum and minimum temperature extremes in the Mediterranean basin using the EOBS and ERA5-Land datasets for the period 2011–2023. EOBS is a daily gridded land-only observational dataset over Europe while ERA5-Land is a global climate reanalysis dataset with hourly resolution and global coverage, both with a spatial resolution of 0.1°x0.1°.

In this study, climatic extremes were analysed. All values exceeding the 90th percentile of the data distribution or falling below the 10th percentile were used to identify extreme warm and cold temperatures, respectively. The main objective is to compare the distributions of temperature extremes for the two datasets to identify differences in the amount and magnitude.

The analysis was conducted on five climatic sub-regions of the Mediterranean Basin, including the Iberian Peninsula, Southern France–Balearic Islands, Northeastern Mediterranean, and the Southeastern Mediterranean with Turkey.

Preliminary results reveal that the number of temperature extreme detected simultaneously by the two datasets is about 80%. The best agreement between EOBS and ERA5-Land is found in the regions densely covered by near-surface measurement stations. More specifically, EOBS identifies more intense warm extremes than ERA5-Land, with most of the values ranging between 31–34 °C. For warm extremes, EOBS also captures a broader range of extreme temperature values compared to ERA5-Land in some areas, such as the Iberian Peninsula and the Southeastern Mediterranean. In both datasets, the values are characterized by temperatures ≥40°C, which represent 20% of the value above the percentile threshold. For cold extremes, the two distributions show a good agreement with approximately 25% of the values ​​on average between -4°C and 0°C, in areas such as the Iberian Peninsula and the Western Mediterranean, while lower values between -10°C e -6°C are observed in the Eastern Mediterranean. In the Iberian Peninsula and Western Mediterranean, EOBS shows a higher cumulative probability for values lower than -10 °C, while ERA5-Land has a higher cumulative probability in the range from 0°C to -2 °C. In the Northeastern Mediterranean, the cumulative probability for temperatures < -10 °C is approximately 25% for both datasets.

Further consideration will be presented regarding the influence of orography on the differences observed between ERA5-Land and EOBS, to better understand the representation of climatic extremes in both datasets.