China–Korea Linked Typhoons: A transboundary sequential hazard framework for East Asian tropical cyclones

Abstract. Tropical cyclones over the western North Pacific (WNP) are among the most damaging natural hazards in East Asia, yet the transboundary sequential process by which a single typhoon affects China and then Korea has not been quantified. This study proposes the China–Korea Linked Typhoon (CKLT) framework and applies it to 70 years of official records (1949–2018) from the China Meteorological Administration (CMA) and the Korea Meteorological Administration (KMA). A CKLT is defined by three criteria: (i) the same WNP typhoon number appears in both CMA and KMA records; (ii) the China impact onset precedes or coincides with the Korea impact onset; and (iii) the Forecast Window (FW), defined as the interval between the two onsets, does not exceed 14 d. The FW is an observational temporal linkage metric, not a forecast skill measure. The 14 d threshold is jointly supported by Gaussian mixture model decomposition, kernel density estimation, and physical transit-time considerations, with the resulting case count stable across thresholds of 12–19 d. Mann–Kendall analysis revealed asymmetric long-term changes: China-affecting typhoon frequency in the CMA W8 station record increased (+ 0.570 events decade⁻¹, p = 0.006; constant-network subset + 0.45 events decade⁻¹, p = 0.032) while station-based mean wind and gust decreased; Korea-affecting typhoons in the KMA advisory record showed no frequency trend but exhibited intensification in advisory-based extreme gusts (+ 1.41 m s⁻¹ decade⁻¹, p = 0.022) and typhoon-conditional precipitation (+ 24.7 mm decade⁻¹, p < 0.001). Of the 227 Korea-affecting typhoons, 75 shared a common WNP typhoon number with CMA records and satisfied the sequential onset criterion; applying the 14 d Forecast Window threshold identified 36 (15.9 %) as CKLTs, with the FW distribution adequately represented by a parsimonious gamma model (α = 1.20, β = 5.21; KS p = 0.258) and a 6 d median (95 % bootstrap CI [2.95, 6.78] d; B = 5000). These results support the CKLT framework as an observation-based, population-level timing indicator for transboundary typhoon hazard analysis and bilateral disaster-preparedness research, rather than as a deterministic forecast of individual storm impacts.