Modelagem numérica das ondas de tempestade na costa de Moçambique: o caso dos ciclones Idai e Kenneth

Abstract

This study analyzed the storm surges generated by tropical cyclones Idai and Kenneth (2019) along the Mozambique coast using the CROCO model at 1/12° resolution. Three experiments were conducted for each cyclone (Tide+Wind, Tide-Only, Wind-Only), allowing the decomposition of total sea level elevation and quantification of nonlinear interactions. Validation with tide gauge data from Pemba and Inhambane (2007) revealed R² = 0.969 and RMSE = 0.221 m at Pemba, and R² = 0.850 and RMSE = 0.349 m at Inhambane. Harmonic analysis showed overestimation of semidiurnal constituents (+17.1% for M2) and underestimation of diurnal constituents (−12.2% for K1) at Pemba, a pattern attributed to bathymetric smoothing. Astronomical tide proved dominant, contributing ~92% to Idai and ~97.8% to Kenneth, confirming the meso macrotidal nature of the western costal shelf of Mozambique Channel. Residual surge reached +0.823 m at Beira and +0.107 m at Pemba , a 7.7‑fold difference explained by three factors: wind stress ~3.3 times higher during Idai; morphological amplification over the Sofala Bank; and favorable timing (Δt = −6.0 h for Idai versus 5.0 h for Kenneth). Nonlinear interaction was systematically negative (mean −0.256 m at Beira and −0.486 m at Pemba), governed by tidal amplitude rather than cyclone intensity, with the dynamic threshold (𝜇+2𝜎) proving superior to the fixed 2.0 m threshold for identifying extreme events. Results demonstrate that storm surge severity in Mozambique results from complex interactions between atmospheric forcing, tides, and geomorphology, and cannot be predicted solely by cyclone intensity.