The impact of the upward trend in the NAO index on precipitation dynamics in the Mediterranean region

The North Atlantic Oscillation (NAO) is the dominant pattern of atmospheric variability over the North Atlantic region, having its greatest influence on Europe during the winter months. In winter, positive NAO index values are linked to warmer temperatures and increased precipitation in western and northern Europe, whereas southern Europe tends to experience colder and drier conditions. These drier conditions can pose significant challenges for agriculture and livelihoods. An overall positive trend in the NAO index has been observed in winter in recent decades. However, how precipitation dynamics in the Mediterranean region respond to the shift towards a higher NAO index are largely unknown, partly due to the poor capture of NAO’s upward shift in climate models. 

Here we examine the impact of the shift towards a higher NAO index on precipitation dynamics in the Mediterranean region in winter. We employ a novel statistical model to analyse next-day precipitation conditional on past observations. The analysis focuses on conditioning drought persistence on different NAO states to assess their influence on the distributional characteristics of drought durations across the Mediterranean region. We present preliminary analyses that contribute to the growing body of evidence that long-term positive trends in the NAO index have an impact on rainfall patterns and drought occurrence in Europe. Understanding the role of teleconnections in regional climate variability and long-term trends is essential for robust regional climate projections for improved risk assessment and policy planning.