Temporal Analysis of Mean Sea Level and Characterization of Extreme Climate Events in Guanabara Bay, Rio de Janeiro (1989–2021)

Coastal management aimed at mitigating the effects of sea level rise and extreme events has become an increasing concern. This requires strategies based on risk assessments, vulnerabilities, and impacts associated with various climate scenarios. In this context, the present study aims to evaluate changes in mean sea level and characterize the occurrence of extreme events in the Guanabara Bay. The focus is on the seasonality and evolution of the time series recorded by the tide gauge at Ponta da Armação in Niterói, RJ, from 1989 to 2021. The study estimates the rate of sea level rise, the frequency of extreme events exceeding ±2 and ±3 standard deviations, and the evolution of harmonic components (amplitude and phase) over both annual and 19-year periods. The average rate of sea level rise was determined to be 2.66 ±0.45 mm/year. Residuals were crucial in identifying anomalies and distinguishing extreme over-elevation events, which predominantly occurred in the autumn (54.62%) and the winter (34.63%). The most intense events, exceeding ±3 standard deviations, displayed strong seasonality, with positive peaks in the autumn (66.20%) and negative peaks in the winter (44.33%). The analysis of harmonic components revealed positive trends in the amplitudes of the annual series for M2 and S2, alongside variations in the phases of M4, N2, and Q1. These results suggest significant changes in the dynamics of sea level variations in the region over the studied period.