Md. Rezuanul Islam , Masaki Satoh, Yohei Sawada, Le Duc

Variability in storminess, storm surge, and mean sea level (MSL) can substantially alter coastal hazards associated with extreme sea levels (ESL). However, detection and attribution of past changes in tropical cyclone (TC) and related storm surge activity are hampered by inhomogeneous TC records due to changes in observational capabilities. Here we investigate spatiotemporal changes in storm surge levels in Japan from 1980–2019, a period when observational platforms including tide gauges and storm records are highly consistent. The analyses illustrate statistical evidence of increasing surge annual maxima in several places including the bay area of Tokyo since 1980 and this rate of change is comparable to those observed for MSL rise over the same period. These findings contrast the current hypothesis on the flood adaptation plan in which future surge extremes will remain the same. We demonstrate that the change in surge annual maxima reflects the combined effect of a consistent northeastward shifting of TC landfall location, intensifying and widening of TC. The substantial influence of these TC meteorological variables on surge levels coupled with MSL rise over long periods suggests that current coastal planning practices including critical heights for flood defenses, might be inadequate in the future.