Past, present and future of wave climate, storms and morphological impacts on sandy coasts: Spain and Wales coasts examples.

Abstract:

Coastal response to climate events is very important for both socio-economic and environmental reasons. In order to carry out a correct coastal management program, it is important to provide realistic analysis of the natural variability and trend associated with climatic events (i.e. hurricanes, storms). In a scenario of rising sea level and increasing wave heights, the coastline will suffer huge impacts in terms of erosion and flooding especially with respect to low-lying regions that may partly or entirely disappear. This work deals with the analysis of a 22 year long wave buoy dataset recorded at Cadiz (SW Spain) and Tenby (S Wales, UK) with the objective of find the existing relationships between wave climate and coastal response. The analysis consisted in the characterization of winter wave climate, extreme waves and storms characteristics and distribution and their relationships with regional cycles (Teleconnection Patterns) such as the North Atlantic Oscillation (NAO) Index, the East Atlantic (EA) pattern and the Arctic Oscillation (AO), among others. Wave climate showed clear cyclic variations in average monthly significant wave height (Hs). Winter waves rapidly increased in height, reaching peak values (Hs = 1.2 m, Cadiz, Hs = 2.1 m, Tenby) between December and January. Energy patterns calculated using the equation of wave energy flux, showed average values of 37 kW/m and 155 kW/m respectively, during winter. In the same way, storm characterization in each study area was carried out using the Storm Power Index (Dolan and Davis, 1992) and five classes were obtained, from class I (weak) to V (extreme). Storm occurrence probability was 95% for class I (i.e. almost one event per year) to 5 % for class V. The return period for class V was 25 years and ranged from 5 to 8 years for classes III and IV storms, e.g. significant and severe events. Classes I and II showed a period of recurrence ranging from 1 to 3 years. For both areas high energy wave values were observed when neutral to strong negative NAO and AO phases occurred and also when there were abrupt changes moving between positive and negative phases without passing through a neutral phase. Beach response to storm events greatly varied along both investigated littorals, and essentially depended on the sequence of storm events and the beach morphodynamic state.