Regionalization of Tidal Harmonic Constants as an Alternative to Global Tide Models: An Assessment in Brazilian Coastal Environments

Abstract

Harmonic tide prediction plays a fundamental role in nautical cartography, coastal geodesy, and sea-level monitoring. This study presents a comparative assessment of tide predictions derived from three distinct sets of harmonic constants: the local FEMAR catalog, the regionalized IBGE_REG dataset obtained through spatial interpolation of harmonic constants from the Brazilian Permanent Tide Gauge Network for Geodesy (RMPG/IBGE), and the global FES2022 model. The analysis was carried out in two contrasting coastal environments: Todos os Santos Bay, characterized by high hydrodynamic complexity, and the Rio de Janeiro coastline, representative of a predominantly open-coast setting. Predicted time series were compared with observations after temporal alignment using cross-correlation and mean-level adjustment and evaluated using the root mean square error (RMSE), residual standard deviation (STD), and coefficient of determination (R²). In Todos os Santos Bay, predictions based on the FEMAR constants and the IBGE_REG dataset achieved superior performance, with RMSE values ranging from approximately 0.08 to 0.14 m and coefficients of determination exceeding 0.95, whereas the global model exhibited higher residual variability at some stations. Along the Rio de Janeiro coast, all approaches showed comparable performance, with RMSE values ranging from approximately 0.12 to 0.17 m and high R² values for all evaluated models. The results demonstrate that harmonic constant regionalization provides a technically consistent approach for extending the spatial coverage of tide predictions in regions lacking local harmonic analyses, particularly in hydrodynamically complex coastal environments, while the global FES2022 model remains a competitive alternative in predominantly open-coast settings.