South-west Japan lashed by powerful typhoon: 18-19 September 2022
One of the biggest storms to hit Japan in decades, super typhoon Nanmadol triggered landslides and brought record-breaking rain to south-west Japan. Two people have died and 90 were left injured, whilst nine million people were told to evacuate their homes (BBC, 2022). Around 130,000 households suffered power outages – most of them were in the southernmost Kyushu region, which saw the worst of the rainfall (Guardian, 2022). Nanmadol became the fourteenth numbered typhoon to hit the island nation which is by now no stranger to this natural hazard (Asahi Shiumbun, 2022).
Event overview
Japan is a frequent victim of natural disasters due to its location on the Pacific Ring of Fire and its exposure to Western Pacific typhoons, of which Typhoon Nanmadol is the latest one to make landfall. Nanmadol approached the island of Kyushu from the south and made landfall on Sunday 18 September near the city of Kagoshima. A rare “special warning” was issued by Japan’s Meteorological Agency (JMA) with Level 4 evacuation instructions issued to residents in and around Kyushu (Al Jazeera, 2022). Two fatalities have been reported so far, including a man who was found in a car that was submerged in Miyazaki Prefecture (Japan Times, 2022a).
By 20 September the storm had passed over Japan and headed eastwards into the Pacific Ocean (Guardian, 2022), leaving scenes reminiscent of those caused by Typhoon Hagibis in 2019 (see a previous JBA report for an overview of this event).
In order to assess the extent of the typhoon’s damage, Japan’s Prime Minster Fumio Kishida rescheduled his flight to New York, where he was to attend the UN General Assembly (Financial Times, 2022). Yoshiyuki Toyoguchi, a representative from Japan’s Ministry of Land, Infrastructure, Transport and Tourism, remarked that “flooding is affecting some areas and there are still many details of the damage we’re yet to grasp” (IBTimes, 2022).
Meteorological Overview
Typhoon Nanmadol was a super typhoon with strength equivalent to a Category 5 hurricane, sustaining high wind speeds of over 240km/h as it made its way towards south-eastern Japan (Japan Times, 2022b; BBC, 2022).
Nanmadol began life as a tropical depression over the sea south of Japan on 13 September (local time), developing into a tropical storm later that day; by 15 September it had evolved into a typhoon, further intensifying into a super typhoon on 16 September (Wunderground, 2022). The chronological development of the typhoon is shown in Table 1 and Figure 1.
Table 1: Development of Typhoon Nanmadol (Source: Wunderground, 2022). Dates and times are given in both UTC and local Japan Standard Time (JST).
Typhoon Nanmadol made landfall near the city of Kagoshima in Kyushu, Japan’s southern-most main island, on Sunday 18 September (BBC, 2022). The observed pressure at this point was the fourth lowest on record for a typhoon making landfall in Japan since 1951 (Washington Post, 2022). Nanmadol continued travelling north-eastwards, eventually weakening into an extratropical cyclone and moving offshore into the Pacific on the morning of 20 September (Japan Times, 2022a).
The formation and development of Nanmadol are suspected to have been influenced by warmer than usual sea surface temperatures – as much as 0.5-1.0°C – in the surrounding area, which act to fuel and intensity typhoons. These warmer sea surface temperatures are linked to the ongoing La Niña phase of the El Niño Southern Oscillation, a climate index based on sea surface temperature anomalies in the Southern Pacific Ocean (BBC, 2022; NASA, 2022).
Figure 1: Satellite-observed rainfall animation showing Typhoon Nanmadol’s path between 15 and 20 September 2022. Rainfall data source: NASA GPM, 2022. Typhoon Nanmadol track data source: IBTrACS, 2022. Video produced by JBA Risk Management, 2022.
Impacts
Early warning systems predicted waves reaching as high as 14 metres, with storm surges expected across northern and western Japan (Washington Post, 2022; JMA, 2022a). In response to this, around nine million people were served with evacuation notices across Kyushu, Shikoku and Chugoku (BBC, 2022).
As Nanmadol made landfall, heavy rainfall resulted in flooding across several areas of Japan, particularly in parts of Kyushu where up to 500mm of rain fell in less than 24 hours (Straits Times, 2022a). In Mikyazaki prefecture, in eastern Kyushu, the 24-hour rainfall total exceeded the September monthly average (Japan Times, 2022a); as a result, a local river burst its banks and many residential streets in Kyushu were flooded (Business Times, 2022; Nikkei Asia, 2022). Two fatalities were reported in Kyushu, as well over 100 injuries (Guardian, 2022).
The super typhoon recorded maximum wind speeds of 126kp/h on Tuesday 20 September, causing vehicles to overturn (Japan Times, 2022a). The strong winds reportedly damaged parts of Tanegashima Space Center, south of Kyushu (DW, 2022), whilst saturated ground resulted in landslides, damaging electric lines and leaving hundreds of thousands of homes without power (Japan Times, 2022b).
The resulting floods, wind and landslides forced several transportation lines to halt. Tokyo’s Tozai underground line and Kyushu’s bullet train, ferries and airlines all suspended their service, and hundreds of flights were cancelled (BBC, 2022). Ground transportation resumed on 20 September, after a three-day long suspension (Guardian, 2022).
Early modelled loss projections are anticipating losses in the low single-digit billions of US dollars (Insurance Insider, 2022), the majority of which Yale University’s Climate Connections estimate will be attributable to flooding alone (Forbes, 2022). However, Nanmadol is not anticipated to severely impact the insurance industry, in part due to Japan’s robust capital and strong reinsurance programs (Artemis, 2022).
Recent significant historical events
Table 2. Three recent historical flood events and their impacts across Japan.
Event analysis
The greatest rainfall amounts from Nanmadol were experienced in the southern island of Kyushu, with over 400mm of rain falling in some areas (Guardian, 2022; AccuWeather, 2022). The NHK news organisation reported over 900mm of rainfall in the town of Misato in Miyazaki prefecture over the course of the weekend, exceeding the September monthly average (NHK, 2022). The city of Ebino, nestled in the plateau of the Kirishima mountain range in Miyazaki, recorded a daily total exceeding 700mm between 18 and 19 September (Floodlist, 2022). The effects of the rain were felt elsewhere too, with the Chugoku area - west of Honshū island - experiencing record-breaking rainfall towards the latter part of the weekend, causing the Takatsu and Ota rivers to exceed flood levels (Japan Times, 2022c).
Figure 2: Mean daily rainfall accumulation (in mm) over municipalities of Kyushu Island between 17 and 19 September 2022. Data source: NASA GPM (2022), graphic produced by JBA (2022).
Return period analysis
JBA conducted extreme rainfall return period analysis for three locations – Kitikata and Nishimera in Miyazaki prefecture, and Saiki in Ōita prefecture – using NOAA CPC gridded daily climate data spatial resolution of 0.5 degrees, recorded between 1979 and present day (NOAA, 2022).
Table 3: 24-hour recorded precipitation at various locations on Kyushu Island, recorded between 18:00 JST 18 September to 18:00 19 September. Source: JMA, 2022b.
The results of the analysis are shown in Figures 3, 4 and 5. A Generalised Pareto Distribution curve was fitted to the historical data at each location to give an exceedance probability curve, shown by the solid orange line, with the 70th percentiles given by the dashed lines. The 24-hour rainfall totals recorded at the sites (listed in Table 3) are represented by the blue line and enable the return period of the extreme rainfall event to be estimated. The results of the analysis reveal the return period of the extreme rainfall to fall between approximately 150-300 years at these locations.
Figures 3, 4 and 5: Estimated extreme rainfall return periods at (left) Saiki, (middle) Nishimera and (right) Kitikata on Kyushu Island, based on NOAA CPC gridded climate data. Rainfall totals recorded between 18 September 18:00 JST and 19 September 18:00 JST are shown in context by the blue horizontal lines. CPC Global Unified Gauge-Based Analysis of Daily Precipitation data provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov.
JBA Risk Management’s Japan Flood Maps
JBA have national 30m resolution river (fluvial) and surface water (pluvial) flood hazard maps for Japan, which were updated earlier this year using the most up-to-date science and methods. Our recent updates incorporate the latest terrain and land use data, as well as updated information on flood defences and improved classification of river and surface water flood types. Figures 6 and 7 show that JBA’s flood maps at a return period of 200 years capture areas known to have flooded as a direct result of Typhoon Nanmadol.
For more information on our recent map updates, please see the following link: https://www.jbarisk.com/news-blogs/japan-flood-map-update-2022/
Figures 6 and 7: JBA’s river (blue) and surface water (purple) flood hazard maps showing flood extents for a 1-in-200-year event. Reported flood locations in Miyazaki Prefecture are shown in context (green circles) at Kunitomi, Higashimorokata District (Figure 6) and Shintomi, Kotu District (Figure 7).
If you're interested in finding our more about how our products or services can improve your management of flood risk, please get in touch for more information.
This report is covered by JBA’s website terms – please read them here.
References
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