Atmospheric controls and long range predictability of directional waves
in the United Kingdom & Ireland
Abstract
Improved understanding of how our coasts will evolve over a range of
time scales (years-decades) is critical for effective and sustainable
management of coastal infrastructure. Globally, sea-level rise will
result in increased erosion, with more frequent and intense coastal
flooding. Understanding of current and future coastal evolution requires
robust knowledge of the wave climate. This includes spatial, directional
and temporal variability, with recent research highlighting the
importance of wave climate directionality on coastal morphological
response, for example in UK, Australia and California. However, the
variability of the inshore directional wave climate has received little
attention, and an improved understanding could drive development of
skillful seasonal or decadal forecasts of coastal response. We examine
inshore wave climate at 63 locations throughout the United Kingdom and
Ireland (1980–2017) and show that 73% are directionally bimodal. We
find that winter-averaged expressions of six leading atmospheric indices
are strongly correlated with both total and directional winter wave
power (peak spectral wave direction) at all studied sites. Coastal
classification through hierarchical cluster analysis and stepwise
multi-linear regression of directional wave correlations with
atmospheric indices defined four spatially coherent regions. We show
that combinations of indices have significant skill in predicting
directional wave climates (r= 0.45–0.8; p<0.05). We
demonstrate for the first time the significant explanatory power of
leading winter-averaged atmospheric indices for directional wave
climates, and show that leading seasonal forecasts of the NAO skillfully
predict wave climate in some regions.