[M-IS06] Extreme Weather and Water Related Disasters in Asia

[MIS06-06] What Drives Extreme Sea Levels in Japan: Unraveling the Dynamics of Storm Surge and Mean Sea Level Trends

★Invited Papers

*Md. Rezuanul Islam¹, Le Duc^1,2, Yohei Sawada^1,2, Masaki Satoh¹ (1.The University of Tokyo, 2.Meteorological Research Institute, JMA)

Keywords:Tropical cyclone, Storm surge, Sea level rise, Extreme sea level, Compound event

Variability in storminess, storm surge, and mean sea level (MSL) can substantially alter coastal hazards associated with extreme sea levels (ESLs). However, the detection and attribution of the past changes in tropical cyclone (TC) activity and associated storm surges are hampered by the inhomogeneous TC records. In this study, we investigate spatiotemporal changes in storm surge levels in Japan from 1980 to 2019, a period when observational platforms including tide gauges and storm records are highly consistent. We find statistical evidence supporting the increase in surge annual maxima in several places including the bay area of Tokyo since 1980. This rate of change is comparable to that observed for MSL rise over the same period. These findings cast doubt on the current hypothesis underlying the flood adaptation plan, which assumes that future surge extremes will remain the same and only considers MSL changes. We demonstrate that the changes in ESL in the last 40 years cannot be explained by the rise of MSL alone. Rather, the northeastward shifting of TC landfall location along with intensifying and widening of TCs, might have altered the likelihood of ESL, including surge extremes. The substantial influence of these TC meteorological variables on surge levels combined with the rise of MSL, suggests that current coastal planning practices including critical heights for flood defenses might be inadequate in the future.