Waves
Recent analyses of global trends in wave height have identified a slight increase in the height of significant waves in average conditions and a greater increase in extreme conditions since 1985. The significant wave height (Hs) in open ocean represents a sea state which is defined as the mean wave height of the highest third of waves. On the Basque coast, where storms predominantly come from a specific direction (WNW-NW), it is one of the most important indicators for characterising the impact of waves.
- Over the last 30 years, no trends have been observed in average wave conditions.
- These trends cannot be directly attributed to climate change, but there is no evidence to rule it out either.
Relationship of the indicator to climate change
Recent studies analysing global wave trends have identified a slight increase in significant wave height in average conditions (0.3 cm/year) and a larger increase in extreme conditions since 1985 (up to 0.8 cm/year for the North Atlantic, Young & Ribal, 2019). In a trend analysis of wave power, Reguero et al. (2019) identified a global increase in wave power of 0.4%/year between 1948 and 2008 that could be associated with warming of the sea surface.
As far as the Bay of Biscay is concerned, wave studies (Castelle et al., 2017, Ulazia et al. (2017), Paris et al. (2014)) have not been able to associate or rule out the relationship of trends to climate change. However, there is a good correlation between seasonal wave height and atmospheric patterns, which requires further analysis. At the same time, the impact of waves on the Basque coast is expected to increase as a consequence of rising sea levels (Liria et al., 2011). An example of this is the municipality of Donostia-San Sebastian, where a non-linear increase in the flood level is expected due to the characteristics of the marine climate, the magnitude of the rise in sea level and the morphology of the profile and protective structures (de Santiago et al., 2020).
Figure 1. Significant wave height Hs (m) from the Bilbao-Vizcaya buoy between 1991 and 2020 (daily average): (A) Original time series data; (B) Partial residuals over the year (dots) and partial seasonal component of the model (grey line with its confidence interval in blue); (C) Partial residuals of the time series for the trend component (blue line).
Analyses of the time series for significant wave height from the Bilbao-Vizcaya buoy show a non-significant increasing trend with a rate of 3.103 cm ± 3.031 cm per decade (p=0.30) (Figure 1) between 1991 and 2020.
Figure 2. Trend in the monthly extremes of significant wave height Hs90 (m) from the Bilbao-Vizcaya buoy between 1991 and 2020.
Analyses of the time series for monthly extremes of significant wave height from the Bilbao-Vizcaya buoy show a significant increasing trend with a rate of 18.317 cm ± 7.573 cm per decade (p=0.0161) (Figure 2) between 1990 and 2020.
In conclusion, no trends have been observed in average wave conditions over the last 30 years, but there has been an increase in certain extreme wave conditions (significant increase in wave height by 18 cm per decade) (Chust et al. 2022).
To characterise the wave height, the trend of the highest values recorded each month can be studied, and can then be compared with the trend for the entire series. The most reliable and comprehensive data on waves in extreme conditions come from buoy data. Therefore, the following indicators have been analysed:
- Significant wave height (Hs) measured from the Bilbao-Vizcaya buoy data
- Monthly extremes in significant wave height (Hs90), calculated with the monthly 90th percentile
Data from the Bilbao-Vizcaya buoy (Longitude: 3.09° W, Latitude: 43.64° N) owned by Puertos del Estado (State Ports) (https://www.puertos.es/) are used to analyse the trend of the significant wave height. The Bilbao-Vizcaya wave buoys began in 1990, and are the longest series of buoys on the Basque coast. Data on significant wave height and other wave parameters are available for every three hours between 1990 and 2002, and every hour from 2002 onwards. A series of monthly values using the 90th percentile calculated each month from the significant wave height series of the Bilbao-Vizcaya buoy has been constructed to analyse the monthly extremes of significant wave heights. The methodology for calculating trends in the time series is detailed in the study by Chust et al. (2022), where a GAMM analysis is used to filter out seasonal variability in the series.
Castelle, B., Dodet, G., Masselink, G. and Scott, T. (2017) A new climate index controlling winter wave activity along the Atlantic coast of Europe: the West Europe Pressure Anomaly: WEST EUROPE PRESSURE ANOMALY. Geophys. Res. Lett., 44.
Chust, G., M. González, A. Fontán, M. Revilla, P. Alvarez, M. Santos, U. Cotano, M. Chifflet, A. Borja, I. Muxika, Y. Sagarminaga, A. Caballero, I. de Santiago, I. Epelde, P. Liria, L. Ibaibarriaga, R. Garnier, J. Franco, E. Villarino, X. Irigoien, J. A. Fernandes-Salvador, A. Uriarte, X. Esteban, D. Orue-Echevarria, T. Figueira, and A. Uriarte. 2022. Climate regime shifts and biodiversity redistribution in the Bay of Biscay. Science of the Total Environment 803:149622.
de Santiago, I., Liria, P., Epelde, I., Chust, G. and González, M. (2020) Estudio de inundabilidad por Cambio Climático en el entorno de las playas del municipio de Donostia-San Sebastián.
Liria, P., Chust, G., Epelde, I. and Caballero, A. (2011) Extreme Wave Flood-Risk Mapping Within the Basque Coast. J. Coast. Res., 225-229.
Paris, F., Lecacheux, S., Idier, D. and Charles, E. (2014) Assessing wave climate trends in the Bay of Biscay through an intercomparison of wave hindcasts and reanalyses. Ocean Dynamics, 52.
Reguero, B.G., Losada, I.J. and Méndez, F.J. (2019) A recent increase in global wave power as a consequence of oceanic warming. Nature Communications, 10, 205.
Ulazia, A., Penalba, M., Ibarra-Berastegui, G., Ringwood, J. and Saénz, J. (2017) Wave energy trends over the Bay of Biscay and the consequences for wave energy converters. Energy, 141, 624-634.
Young, I.R. and Ribal, A. (2019) Multiplatform evaluation of global trends in wind speed and wave height. Science, 364, 548-552.
Bay of Biscay
Wave height
(average)
Wave height
(monthly extreme values)
25.9 – 10.8 cm
Per decade
Time serie between 1990 - 2020