Conclusion

Synoptic Summary (16–22 July)

Between 16 and 22 July 2024, central Korea experienced a prolonged extreme rainfall event, not from a single frontal passage but from a sequence of wave cyclones along a quasi-stationary front. This event was driven by three key factors:

a persistent southwesterly low-level jet (LLJ) transporting moisture from the East China Sea
repeated formation of surface mesocyclones that anchored the front
a cut-off low over Liaodong interacting with a downstream ridge over Japan, maintaining upper-level divergence for 72 hours.

Though atmospheric instability (CAPE) remained low, the environment supported intense rainfall due to high moisture content (TPW 50–70 mm), strong θₑ gradients, and episodic CIN breakdown. These conditions favored warm-rain processes and isentropic ascent, leading to multiple rainfall peaks (18, 19, and 21 July) tied to wave and LLJ pulses—marking a moisture-driven, dynamically sustained system, rather than a typical monsoonal pattern.

Comparison with Past Events

This event shares clear similarities with the Seoul urban flood on 27 July 2011, which was in mesoscale structure and synoptic evolution.

In both cases, a quasi-stationary upper-level trough–ridge pattern remained locked in place, sustaining continuous upper-level divergence directly above a stalled frontal boundary. This persistent lifting mechanism led to prolonged heavy rainfall.

Like in 2024, convection was dominated by warm-rain processes, with only modest atmospheric instability (low CAPE). This means that high rainfall efficiency, rather than severe convective energy, was the key factor behind the flooding.

Both events also showed multiple redevelopment phases of the frontal rainband, which stayed nearly stationary. As a result, the same regions were affected by repeated rainfall peaks, despite the lack of any major frontal movement.

These similarities highlight a broader insight: extreme rainfall in Korea can arise not only from highly unstable atmospheres, but also from moist, dynamically forced environments where frontal structures are locked in place.

Statistical Analysis

The extreme precipitation event that occurred across South Korea during 16–22 July 2024 exhibited highly anomalous characteristics in both intensity and spatial concentration. Analyses of maximum 1-hour and daily precipitation revealed that several stations, including Paju, Namhae, and Seosan, recorded values that not only exceeded historical records but also corresponded to statistically rare return periods exceeding 200 years in some locations. The event was marked by exceptionally high Local Intensity Ratios (LIR) and Concentration Indices (CI10%), indicating that a substantial portion of seasonal precipitation was concentrated within a few hours or days, particularly at coastal and northern inland stations. Despite this intensity, the event was not characterized by prolonged rainfall durations or frequent high-intensity episodes, but rather by isolated, short-lived, and extremely intense downpours.

When compared against the 1991–2020 climatology, the 2024 event consistently ranked at or above the 95th percentile across multiple metrics at key stations. This suggests a strong deviation from historical norms, likely indicative of an evolving hydroclimatic regime. The spatial heterogeneity of the event, with stark contrasts between affected and unaffected regions, underscores the growing importance of localized risk assessments and high-resolution monitoring in extreme weather prediction and disaster preparedness. These findings reinforce the necessity of updating intensity-duration-frequency (IDF) curves and regional design standards to reflect the emerging realities of short-duration, high-impact precipitation events in a changing climate.

Forecasting Improvements and Policy Implications

1. Forecasting Enhancements

500 / 300 hPa charts: A cut-off low stuck over Liaodong and a strong ridge over Japan suggest persistent upper-level divergence, which supports long-lasting ascent and rainfall.
850 hPa θₑ gradients and LLJ analysis: If a θₑ ridge aligns with the Korean Peninsula and a low-level jet stronger than 25 kt hits this region, strong frontal lifting is likely.
Skew-T analysis: Instead of focusing only on CAPE, it’s more helpful to track precipitable water (TPW), CIN (convective inhibition) breakdown, and LCL (lifting condensation level) height to evaluate rainfall potential.
Satellite and radar imagery: Very cold cloud tops (IR temperature < −70°C) combined with radar echo training patterns indicate anchored convection and flash flood potential.

2. Policy Implications

Shift from simply monitoring rainfall totals to identifying high-risk synoptic patterns, such as prolonged wave-train activity and upper-level blocking.
Strengthen localized flood warning systems, especially in urban basins and river valleys prone to flash flooding.
Enhance forecast interpretation by factoring in multi-wave cyclogenesis and frontal regeneration, rather than assuming a single rain event tied to one frontal passage.