Influence of the North Atlantic Oscillation at local and regional scales: a case study of the Belgian coast. (3rd August 2018) - Montreuil, Anne‐Lise
Abstract : Together, large‐scale atmospheric circulation and local winds determine the occurrence of storm surges that may result in disastrous erosion. This study investigates the interrelationships between large‐scale atmospheric flow and local wind regimes as driving factors of erosion at the Belgian coast. The large‐scale atmospheric circulation is examined in terms of the winter North Atlantic Oscillation (NAO) index, and it is analysed and compared with regional‐scale circulation patterns (i.e. circulation weather types) and local wind regimes, on both annual and seasonal timescales. The results indicate that a strengthening of the positive winter NAO phase can result in an increase in the frequencies of west (W), southwest (SW) and northwest (NW) directional weather types, leading to local wind speeds in excess of 8ms −1, propagating towards the coast. These conditions are likely to lead to erosive events at the coast. By contrast, a weakening of the winter NAO phase can favour the development of northeast (NE), north (N), east (E) and southeast (SE) weather types. The NE and E types generate particularly strong winds, which potentially worsen erosion at the coast. The E and SE types do not, however, affect wind at a local scale. Thus, the extent to which the wind regime at the Belgian coast is sensitive to the winter NAO is a function of the equilibrium between the NAO effects and the regional atmospheric flow direction. In this study, a downscaling conceptual model is developed which relates climate to large‐scale and local‐scale coastal erosion forcing factors. A better understanding of the variability of, and the interrelationships between, climate, meteorology and erosion can help us to adapt to the changes in coastal evolution driven by climate change, improving the prospects of long‐term coastal resilience. Abstract : – A downscaling conceptual model is developed which relates climate to large‐scale and local‐scale coastal erosion forcing factors. – Whether or not the wind regime at the coast is sensitive to the winter NAO is a function of the equilibrium between regional atmospheric flow directions. – A strengthening of the positive winter NAO phase results in an increase in the frequencies of W, SW and NW weather types. The image illustrates the downscaling conceptual model of the interrelationships between the winter NAO, various weather types and local wind directions that lead to erosion along the Belgian coast. Unconnected arrows denote little or no influence.