Environ. Res. Lett. 10 (2015) 064011 doi:10.1088/1748-9326/10/6/064011 LETTER OPEN ACCESS Climate change effects on the worst-case storm surge: a case study of Typhoon Haiyan RECEIVED 13 November 2014 REVISED 2 May 2015 ACCEPTED FOR PUBLICATION 27 May 2015 PUBLISHED 11 June 2015 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Izuru Takayabu1, Kenshi Hibino2, Hidetaka Sasaki1, Hideo Shiogama3, Nobuhito Mori4, Yoko Shibutani5 and Tetsuya Takemi4 1 2 3 4 5 Meteorological Research Institute, Tsukuba, Ibaraki 305-0052, Japan University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan Tottori University, Tottori 680-8550, Japan E-mail: takayabu@mri-jma.go.jp Keywords: typhoon, haiyan, storm surge, worst case scenario, climate change Supplementary material for this article is available online Abstract Effects of climate change on the worst case scenario of a storm surge induced by a super typhoon in the present climate are investigated through the case study of Typhoon Haiyan. We present the results of our investigation on super-typhoon Haiyan by using a super high resolution (1 km grid) regional model that explicitly handles cloud microphysical processes. As the parent model, we adopted the operational weekly ensemble experiments (60 km grid) of the Japan Meteorological Agency, and compared experiments using sea surface temperatures and atmospheric environmental parameters from before the beginning of anthropogenic climate change (150 years ago) with those using observed values throughout the typhoon. We were able not only to represent the typhoon’s intensity but also to evaluate the influences of climate change on worst case storm surges in the Gulf of Leyte due to a typhoon with high robustness. In 15 of 16 ensemble experiments, the intensity of the simulated worst case storm in the actual conditions was stronger than that in a hypothetical natural condition without historical anthropogenic forcing during the past 150 years. The intensity of the typhoon is translated to a disaster metric by simulating the storm surge height by using a shallow-water long-wave model. The result indicates that the worst case scenario of a storm surge in the Gulf of Leyte may be worse by 20%, though changes in frequency of such events are not accounted for here. 1. Introduction Human activities have changed the global climate and have affected some extreme weather events (Bindoff et al 2013). A typhoon (i.e., a tropical cyclone or TC) is one of the most potentially destructive extreme weather events. Estimation of the power dissipation index (cube of the maximum surface wind speed integrated for the whole lifetime of the event), a measure of the potential destructiveness of a TC over its lifetime, has already shown that TCs have become stronger in the past thirty years (Emanuel 2005). Moreover, the increase in this index is highly correlated with the observed increasing trend in sea surface temperature (SST) during the same period. However, © 2015 IOP Publishing Ltd studies disagree about whether changes in TC activity can be attributed to human influence, owing to insufficient observations and physical understanding (Bindoff et al 2013). There is increasing interest in whether not only long-term trends of extreme events but also the characteristics of specific recently observed extreme events can be attributed to external drivers and natural climate variability. Simulations to estimate how predicted sea level increases up to 2050 or 2100 will change the probability of future inundations in the eastern coast of the United States on the scale of that caused by Hurricane Sandy (Sweet et al 2013) have indicated that the return period of a similar inundation is likely to decrease.

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