*Article* **Effect of Depth-Induced Breaking on Wind Wave Simulations in Shallow Nearshore Waters off Northern Taiwan during the Passage of Two Super Typhoons**

**Shih-Chun Hsiao 1, Han-Lun Wu 1, Wei-Bo Chen 2,\*, Wen-Dar Guo 2, Chih-Hsin Chang 2 and Wen-Ray Su 2**

1 Department of Hydraulic and Ocean Engineering, National Cheng Kung University, TainanCity70101,Taiwan;schsiao@mail.ncku.edu.tw(S.-C.H.);hlwu627@mail.ncku.edu.tw

 (H.-L.W.) 2 National Science and Technology Center for Disaster Reduction, New Taipei City 23143, Taiwan; (W.-D.G.);(C.-H.C.);wrsu@ncdr.nat.gov.tw(W.-R.S.)

wdguo@ncdr.nat.gov.tw chang.c.h@ncdr.nat.gov.tw **\***Correspondence:wbchen@ncdr.nat.gov.tw;Tel.:+886-2-8195-8611

**Abstract:** Super Typhoons Maria (2018) and Lekima (2019) were adopted for this case study, although they only passed the northern offshore waters of Taiwan without making landfall. A direct modification technique was employed to create the atmospheric conditions for a wave-circulation model to hindcast large typhoon-driven waves. The radius of the modified scale (*Rtrs*) for a hybrid typhoon wind plays an important role in the significant wave height (SWH) simulations during the passage of typhoons. The maximum increment in peak SWH reached 3.0 m and 5.0 m in the deep ocean for Super Typhoons Maria (2018) and Lekima (2019), respectively if the *Rtrs* was increased from 4 × *Rmax* (radius of the maximum wind) to 7 × *Rmax*. The SWHs induced by the typhoon winds in the surf zone were more sensitive to different wave-breaking formulations used in the wave-circulation model. The maximum difference in peak SWH reached 2.5 m and 1.2 m for Super Typhoons Maria (2018) and Lekima (2019), respectively, when the wave-breaking formulations of BJ78 (proposed by Battjes and Janssen in 1978) and CT93 (proposed by Church and Thornton in 1993) were introduced to the wave-circulation model. The SWH simulations in the surf zone were insensitive to the wave-breaking criterion (*γ*) during the passage of typhoons. In shallow nearshore waters, the utilization of a constant *γ* for the wave-circulation model always produces peak SWHs that are smaller than those using *γ* based on local steepness or peak steepness.

**Keywords:** depth-induced wave breaking; wave-breaking formulation; wave-breaking criterion; shallow nearshore waters
