Classification of monthly tidal envelopes in mixed tide regimes.

Coastal inundation is increasing globally. Changes in tidal water levels contribute to flood risk alongside rain and sea storm events. Unlike the latter, temporal variations in tides may be predicted and their patterns analyzed many years in advance. This paper explains two novel methods for characterizing monthly scale patterns in tidal water level variation: one simple qualitative method with restricted applicability; and another more complex quantitative method with global applicability to areas characterized by mixed, mainly semidiurnal and mixed, mainly diurnal tide regimes (~ 65% of global oceans). We reveal that in some areas tidal high and low waters are balanced in near symmetrical patterns, while elsewhere tides are skewed towards upper or lower tidal height envelopes. Areas characterized by tidal patterns skewed towards upper envelopes are at heightened risk of extreme event inundations during certain periods each year, event scale risks that will increase with climate changes. Those skewed towards lower tidal envelopes are prone to frequent flooding and are potentially at greater risk of chronic inundation with ongoing mean sea level rise. Our findings and the novel tidal pattern classification approaches offered contribute to understanding the time varying nature of tidal contributions to coastal inundation risks.