Extreme sea level
Intergovernmental Panel on Climate Change (IPCC) and published by Cambridge University Press in 2023, defines extreme sea level (ESL) as: ‘The occurrence of an exceptionally low or high local sea surface height, arising from (a combination of) short-term phenomena (e.g., storm surges, tides and waves). Relative sea level changes affect extreme sea levels directly by shifting the mean water levels and indirectly by modulating the propagation of tides, waves and/or surges due to increased water depth. In addition, extreme sea levels can be influenced by changes in the frequency, tracks or strength of weather systems and storms, or due to anthropogenically induced changes such as the modification of coastlines or dredging. In turn, changes in any or all of the contributions to extreme sea levels may lead to long–term relative sea level changes. Alternate expressions for ESL may be used depending on the processes resolved. Extreme still water level (ESWL) refers to the combined contribution of relative sea level change, tides and storm-surges. Wind-waves also contribute to coastal sea level via three processes: infragravity waves (lower frequency gravity waves generated by the wind waves), wave setup (time-mean sea level elevation due to wave energy dissipation), and swash (vertical displacement up the shore-face induced by individual waves). Extreme total water level (ETWL) is the ESWL plus wave setup. When considering coastal impacts, swash is also important, and Extreme coastal water level (ECWL) is used.’
See also: Extreme weather and Extreme weather event.
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