Observations of cyclone-induced storm surge in coastal Bangladesh

TL;DR

This study analyzes water level data from tide gauges in Bangladesh to understand cyclone-induced storm surges, revealing that tidal factors often influence water levels more than storm surge alone and that high casualties do not correlate with specific storm characteristics.

Contribution

It provides a detailed analysis of cyclone-induced storm surges in Bangladesh, highlighting the complex interactions between tides, wind, and water levels, and challenges assumptions about direct correlations with casualties.

Findings

Residual water levels are generally smaller than reported storm surge levels.

Water levels are more influenced by tidal phase than storm surge.

No single characteristic predicts cyclone casualties.

Abstract

Water level measurements from 15 tide gauges in the coastal zone of Bangladesh are analyzed in conjunction with cyclone tracks and wind speed data for 54 cyclones between 1977 and 2010. Storm surge magnitude is inferred from residual water levels computed by subtracting modeled astronomical tides from observed water levels at each station. Observed residual water levels are generally smaller than reported storm surge levels for cyclones where both are available, and many cyclones produce no obvious residual at all. Both maximum and minimum residual water levels are higher for west-landing cyclones producing onshore winds and generally diminish for cyclones making landfall on the Bangladesh coast or eastward producing offshore winds. Water levels observed during cyclones are generally more strongly influenced by tidal phase and amplitude than by storm surge alone. In only 7 of the 15 stations does the highest plausible observed water level coincide with a cyclone. While cyclone-coincident residual water level maxima occur at a wide range of tidal phases, very few coincide with high spring tides. Comparisons of cyclone-related casualties with maximum wind speed, hour of landfall, population density and residual water level (inferred storm surge) show no significant correlations for any single characteristic. Cyclones with high casualties are often extreme in one or more of these characteristics but there appears to be no single extreme characteristic shared by all high casualty cyclones.