4-13 July 2020
JBA’s Event Response team has continued to monitor the ongoing flooding across Kyushu, Japan, which has caused 72 fatalities at the time of writing and a further 13 missing persons cases (NHK World Japan).
The original event commentary can be found further below – this is an update as of 14 July 2020.
EXTREME RAINFALL AND IMPACTS IN UPLAND AREAS
Torrential rainfall has continued over the last few days, leading to extensive river flooding across Kyushu.
Analysis of precipitation readings provided by the Japan Meteorological Agency has revealed new record highs of hourly precipitation across Kyushu. Across Kumamoto prefecture, two out of 26 gauges recorded new record hourly rainfall, with five out of 43 gauges setting new records in Kagoshima prefecture (figure 1).
Figure 1: Rain gauges with record breaking 1 hourly rainfall readings for Kumamoto and Kagoshima prefectures during the event. Source: Japan Meteorological Agency.
Multiple prefectures have also seen new precipitation records across 72-hour periods between 6 July and 12 July 2020, including eight records in Kumamoto, four in Kagoshima, five in Fukuoka and nine in Oita. Interestingly, whilst the recorded 72hr maximum at Hitoyoshi did not exceed the maximum previously recorded (on 23 July 2006), all three gauges upstream of Hitoyoshi recorded new maximum rainfalls during this period, contributing to the extreme river flows on the Kuma River which has caused widespread flooding and damage. The accumulated rainfall totals for the duration of the event between 3 July and 14 July 2020 are shown in figure 2.
Figure 2: Accumulation total precipitation 3 – 14 July 2020 for the Kyushu flood event. Source: Japan Meteorological Agency.
WIDESPREAD DAMAGE
This heavy rainfall is forecast to continue across much of Japan over the coming days. According to several news agencies, Japan’s Fire and Disaster Management Agency has estimated 14,000 houses in total to have been flooded or damaged on Kyushu and across western and central Japan (St George & Sutherland Shire Leader). In the Kyushu prefecture of Fukuoka alone, the most recent estimate for the number of damaged homes stands at 4,942 (Fukuoka Disaster Prevention Information).
An estimated 3,700 homes have been damaged in the city of Hitoyoshi, with flood levels reaching 2.5m at the hospital (NHK World Japan). Further downstream, several bridges have been destroyed and numerous riverside communities inundated.
Figure 3 (right): Aerial image showing inundation along the Kuma River (top) (Source: GSI) compared with JBA’s 1 in 200-year river flow map (below).
Landslides have been triggered across multiple prefectures, including 56 in Kumamoto, 44 in Kagoshima, 27 in Nagano and 24 in Nagasaki according to the Land, Infrastructure, Transport and Tourism Ministry (Kyodo News).
Figure 4 (above): Devastation caused by a landslide in the Tagawa area of Ashikita Town on 4 July (top) (Image source: Carl Court / Getty, Jiji Press / AFP / Getty). JBA’s river (blue) and surface water (purple) flood hazard maps highlighting the area at risk across Ashikita District (below).
Japan’s Prime Minister has stated that the Japanese government plans to use over 400 billion yen ($3.74 billion), including reserve funds, for reconstruction work.
RIVER FLOWS AND FLOOD DEFENCES IN URBAN AREAS
Towards the end of last week, the Japan Meteorological Agency issued extreme risk warnings along several downstream river sections. JBA’s Event Response team has been monitoring river flow conditions and the status of flood defences in these highly urbanised areas.
Close inspection of the Geospatial Information Authority of Japan (GSI) aerial imagery taken on Wednesday 8 July has shown limited impact to property and infrastructure in these areas despite extreme flows. In Kurume, Fukuoka prefecture, some limited flooding has occurred across commercial areas in Higashiaikawa. 
Figure 5 (above): Commercial areas inundated in Higashiaikawa, Kurume, Fukuoka prefecture (top) (Source: GSI) compared against JBA’s 1 in 200-year river flood map (below). Coloured points highlighting inundated areas. 
On the opposite bank on the northern side of the Chikugo River, imagery indicates that houses are generally raised above ground level and therefore have not been flooded, despite the widespread flooding of surrounding agricultural land.
Figure 6 (left): Agricultural areas inundated along Chikugo River in Fukuoka prefecture (top) (Source: GSI) compared against JBA’s 1 in 200-year river flood map (below).
JBA’s Event Response team is continuing to monitor this event. To ensure you receive all future event response and company updates, subscribe to our mailing list below.
JBA Risk Management has nationwide return period flood maps for Japan at 30m resolution as illustrated in the report. To find out more about how our maps and models can help you to understand and manage flood risk more effectively, get in touch.
4-6 July 2020
Exactly a year following the devastating flood event in 2019, Kyushu, Japan’s third largest and most south-westerly island, has been affected by wide-scale flooding and deadly landslides over the past week.
Record-breaking rainfall
The Japan Meteorological Agency recorded precipitation highs of 50mm-66mm per hour in the Fukuoka and Kumamoto prefectures between Monday 6 July and Tuesday 7 July. Precipitation highs of around 84mm per hour were recorded in the cities of Kushima, Miyazaki Prefecture, and Kanoya, Kagoshima Prefecture, early on Monday 6 July. Heavy rainfall was also experienced in the central and eastern parts of the island of Kyushu early on Monday 7 July, with totals reaching at least 55mm and 76mm per hour.
Impacts of flooding and landslides across Kyushu
The heavy band of rain has caused widespread flooding and landslides throughout the island of Kyushu, particularly in Kumamoto and Kagoshima prefectures, with over 1.38 million residents advised to evacuate.
Based on information provided by local authorities, a survey undertaken by Kyodo news estimated around 440,000 households across Fukuoka, Nagasaki and Saga prefectures have been advised to evacuate across the island by the evening of 6 July (Kyodo News). Within Fukuoka alone, authorities ordered more than 200,000 households to evacuate, with a further 80,000 households advised to evacuate. However, fewer than 2,000 households were recorded to have left their homes, potentially due to fears of contracting Covid-19 (The Japan Times).
To date, 56 people are reported to have lost their lives as a result of the floods, including fourteen victims in a care home near the Kuma River. The river burst through its levees in several places in the city of Hitoyoshi, Kumamoto, late on Saturday 4 July, flooding low-lying settlements.
The Chikugo River, the largest river in Kyushu, also overflowed in Hita, which is located towards the centre of the island. In Omuta, Fukuoka Prefecture, floods caused around 200 people to become stranded within two evacuation centres.
Tens of thousands of Japanese soldiers have been sent to help rescue stranded citizens and search amongst the wreckage for survivors.
Two examples comparing JBA’s 1 in 1,500-year river flood hazard map (top) and aerial images showing flooding in Hitoyoshi, Kumamoto prefecture. Source of aerial images: Kyodo News.
Outlook
Further heavy rain is forecast over the next few days as warm and humid air flows into the seasonal rain front stretching across the Japanese archipelago. The Japan Meteorological Agency has raised heavy rain warnings across many prefectures across Japan and posted extreme risk warnings for many rivers in central mountainous areas.
(Above, left) Weather warnings by prefecture as of 7 July 2020. Source: Japan Meteorological Agency.
(Above, right) Real-time flood risk map indicating river flood risk levels as of 7 July 2020. Source: Japan Meteorological Agency.
JBA’s Event Response team is continuing to monitor this event.
JBA Risk Management has nationwide return period flood maps for Japan at 30m resolution and a Global Flood Model to help you understand and manage flood risk more effectively. Please get in touch for more information.
References
Updated report
Carl Court / Getty: image source.
Geospatial Information Authority of Japan (GSI). 2020. [online] Available at: https://www.gsi.go.jp [Accessed 14 July].
Japan Meteorological Agency. 2020. [online] Available at: www.data.jma.go.jp [Accessed 14 July].
Jiji Press / AFP / Getty: image source.
Jun, Y. 2020. Heavy rain leaves scores dead. NHK World Japan. [online] 13 July 2020. Available at: https://www3.nhk.or.jp/nhkworld/en/news/backstories/1198/ [Accessed 14 July].
Kyodo News. 2020. PM Abe visits rein-hit Kumamoto to assess damage for recovery measures. Kyodo News. [online] 13 July 2020. Available at: english.kyodonews.net/news/2020/07/8fe657c7bc46-abe-visits-rain-hit-kumamoto-to-assess-damage-for-recovery-measures.html [Accessed 14 July]
St George & Sutherland Shire Leader. 2020. Japan flood death toll up to 68, PM visits. St George & Sutherland Shire Leader. [online] 13 July 2020. Available at: https://www.theleader.com.au/story/6831284/japan-flood-death-toll-up-to-68-pm-visits/?cs=13067 [Accessed 14 July].
Original report
BBC News. 2020. Japan flooding: fourteen dead in flooded care home. BBC News. [online] 5 July 2020. Available at: https://www.bbc.co.uk/news/world-asia-53290211 [Accessed 7 July].
Japan Meteorological Agency. 2020. Weather Warnings/ Advisories. [online] Available at: https://www.jma.go.jp/en/warn/index.html [Accessed 7 July].
The Japan Times. 2020. At least 53 dead as torrential rains and floodwaters hit Kyushu. The Japan Times. [online] 7 July 2020. Available at: https://www.japantimes.co.jp/news/2020/07/07/national/rain-floods-kyushu/ [Accessed 7 July].
Kyodo News. 2020. Death toll rises to 56 as rain damage widens in southwest Japan. Kyodo News. [online] 7 July 2020. Available at: https://english.kyodonews.net/news/2020/07/23ba8d55a443-death-toll-rises-to-50-in-rain-hit-southwestern-japan.html [Accessed 7 July].
Mealey, R. 2020. Japan floods: 11 missing, 500,000 to evacuate after days of torrential rain in Fukuoka and Oita. ABC News. [online] 6 July 2020. Available at: https://www.abc.net.au/news/2017-07-06/japan-floods-almost-500000-asked-to-evacuate/8684472 [Accessed 7 July].