Investigation of the interrelation between climate change, the North Atlantic Oscillation and extreme events in the Mediterranean Region

The Mediterranean region is considered a hotspot of climate change because it is warming faster than the rest of Europe and undergoing more drastic changes in its hydrological cycle. As a result, hydro-meteorological extremes, such as droughts and periods of heavy precipitation, are more frequent and intense compared to other regions. Significant interannual-to-decadal variability in this region is modulated by large-scale atmospheric modes, particularly the North Atlantic Oscillation (NAO). This study examines the dynamic relationship between different NAO phases and their potential modulation under climate change, as well as the occurrence of extreme events across the Mediterranean, with a particular focus on Greece. For this purpose, we utilised NAO index data from the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), in conjunction with ERA5 atmospheric reanalysis data, Standardised Precipitation-Evapotranspiration Index (SPEI) data and Expert Team on Climate Change Detection and Indices (ETCCDI) data, to characterise the extremes (droughts, heatwaves, and heavy precipitation). To isolate the evolution of extremes relative to defined NAO+ and NAO- events, we used composite and superposed epoch analysis. The statistical significance of the results was assessed via the Monte Carlo bootstrapping technique. Our preliminary results suggest that the climate change-driven warming trend may alter the amplitude of NAO-related impacts, potentially intensifying the risk of heatwaves during NAO+ summers and amplifying the contrast between the occurrence of droughts and floods.

Keywords: Hydro-meteorological extremes, North Atlantic Oscillation, Climate Change, Mediterranean

Acknowledgements: This work is supported by National Funds by FCT – Portuguese Foundation for Science and Technology, under the projects UID/04033/2025: Centre for the Research and Technology of Agro-Environmental and Biological Sciences (https://doi.org/10.54499/UID/04033/2025) and LA/P/0126/2020 (https://doi.org/10.54499/LA/P/0126/2020).