Future Change Storm Surge based on Multi-Scenario and Multi-Regional Climate Model Ensemble Experiments

Future Change Storm Surge based on Multi‐Scenario and Multi‐Regional Climate Model Ensemble Experiments Kanazawa Univ. Junichi Ninomiya Kyoto Univ. Nobuhito Mori Tetsuya Takemi Tsukuba Univ. Osamu Arakawa Nagoya Univ. Sachie Kaneda Masaya Kato

Outline • Motivation • Summary • Methodology • SST ensemble experiment using MRI‐AGCM • RCM and Storm surge model and setting • Results • Sensitivity of future change parameter for TC simulation • Future change of TC • Storm surge simulation using RCM outputs and the other method • Summary

Motivation • Subjects • Uncertainty for future change estimation • Extreme event assessment based on coarse‐resolution GCM • Aims • To decrease uncertainty for GCM and RCM bias, and estimate probable extreme event by careful simulations. • To evaluate future change of largest storm surge. ‐> To make management plan for coastal structures • This research is case study of pseudo global warming (PGW) experiment with historical typhoon Vera (1959).

Summary • A series of delicate RCM simulations • RCM hindcast gave reasonable result. • Partial future change parameter for RCM simulation estimated excessively strong TC. • All future TCs intensity were stronger than present TC and their tracks change to west. (WRF: 9.3 hPa, JMA‐NHM: 29.7 hPa) • Future change of storm surge • Storm surge simulations using empirical TC model based on fine RCM output were carried out. • Estimated storm surge future changes by forcing from WRF, JMA‐NHM and ensemble mean were 26 cm.

Methodology 1. Estimate future change of atmospheric parameters based on SST ensemble experiments using MRI‐AGCM (RCP 8.5, 20 km‐resolution, Mizuta et al., 2014) ‐> 4 kinds of future change distribution 1. 2. Ensemble average of CMIP5 (C0) 3 kinds of SST distribution calculated by cluster analysis (C1 – 3) 2. Present‐ and Future‐RCM simulation of TY Vera using 2 RCMs 1. Present‐experiments (Pre) using JRA‐55 2. Future‐experiments (PGW; Pseudo Global Warming, C0 – 3) 3. Storm surge simulation using RCM outputs

SST Ensemble Exp. • Mizuta et al. calculated using MRI‐ AGCM with 4 SST distributions.

Future Change Distribution from MRI‐AGCM Ensemble average Increase 3 – 4 K over sea Difference between each cluster and ensemble avg. ±10 – 15 % scattering compared with ensemble average of future change

Methodology 1. Estimate future change of atmospheric parameters based on SST ensemble experiments using MRI‐AGCM (RCP 8.5, 20 km‐resolution, Mizuta et al., 2014) ‐> 4 kinds of future change distribution 1. 2. Ensemble average of CMIP5 (C0) 3 kinds of SST distribution calculated by cluster analysis (C1 – 3) 2. Present‐ and Future‐RCM simulation of TY Vera using 2 RCMs 1. Present‐experiments (Pre) using JRA‐55 2. Future‐experiments (PGW; Pseudo Global Warming, C0 – 3) 3. Storm surge simulation using RCM outputs

Models • RCM • WRF v3.3.1 • JMA‐NHM • Japan meteorological agency, non‐hydrological model • Work for weather forecast in Japan • Storm Surge model • SuWAT • Coupled model of Surge, Wave and Tide • Developed by S. Y. Kim (3rd presenter in this session)

Model settings (WRF, JMA‐NHM & SuWAT) 895 hPa Domains for storm surge model 7290 m 20 km 2430 m 810 m Item WRF settings Duration 1959/9/22 12:00 – 9/27 0:00 Spatial Res. 5 km Grids 976 x 831 Vert. Lay. 56 Dt 20 s Micro. WSM 6‐class Shortwave RRTMG Longwave RRTMG Surface Bound. Revised MM5 Monin‐Obukhov Planet. Bound. YSU Land Surf. 5‐layer Thermal diffusion Cumulus Kain‐Fritsch Urban w/o Topo. & Landuse USGS GTOPO30 Nudging Spectral Nudging（Wave Num. 2，Upper layer of 700hPa） Bogus Initial

Sensitivity of Future Change Parameter Case Name future change Param. Min. Cen. Pres. [hPa] BestTrack w/o 895 Pre w/o 901.8 C0 SST SST 859.7 C0 SST/T SST, T 889.4 C0 SST/T/P SST, T, P 893.0 T: Temp., P: 3D Pres. n/a Humidity: Future change is small. Wind: It will change TY track. Case C0 SST estimated very strong typhoon due to intensification of atmospheric instability.

Pre & PGW experiments using RCM Case Name Param. future change Min. Cen. Pres. [hPa] BestTrack w/o 895 WRF Pre w/o 901.8 WRF PGW SST, T, P 892.6 JMA‐NHM Pre w/o 907.0 JMA‐NHM PGW SST, T, P 877.3 T: Temp., P: 3D Pres. Landfall

Storm Surge using WRF Pre & PGW Original WRF Outputs Pre experiment ・Slow TY moving ・Large TY eye ‐> Late and small peak surge PGW experiments ・Westward track drift ‐> Small peak

Storm Surge Sim. under Pre & PGW Target using WRF outputs Original WRF Outputs Track shift Estimated Shifted WRF Outputs BestTrack Shifted TC Estimated TC Pre using shifted WRF output ・Good agreement PGW using shifted WRF output ・Small peak <‐ influenced surface roughness on land ・Preでは，観測に⽐べて台⾵の遅 れと中⼼付近の再現性の影響を受 けた結果，ピーク時間の遅れと過 ⼩評価となった． ・PGWでは，経路の⻄側へのズレ により過⼩評価となった．

Storm Surge Sim. under Pre & PGW using WRF outputs WS>40m/s 20<WS<40m/s Due to difference of surface roughness between over land and over sea.

Summary of Storm Surge using WRF Track shift & empirical TC Forcing BestTrack Estimated □︓RCM output △︓Shifted RCM output ＊︓Empirical TC model Pre，C0，C1，C2，C3 Estimated TC Empirical TC Central Pres. Max. Wind Radius It is difficult to compare with surge results using RCM output each other because of track mismatch and difference of moving speed. Experiments using empirical TC model are effective to investigate TY intensification.

Summary • A series of delicate RCM simulations • RCM hindcast gave reasonable result. • Partial future change parameter for RCM simulation estimated excessively strong TC. • All future TCs intensity were stronger than present TC and their tracks change to west. (WRF: 9.3 hPa, JMA‐NHM: 29.7 hPa) • Future change of storm surge • Storm surge simulations using empirical TC model based on dynamical DS were carried out. • Estimated storm surge future changes by forcing from WRF, JMA‐NHM and ensemble mean were 26 cm, 26 cm and 26 cm, respectively.