Vietnam Floods: A Tale of Six Cyclones

October 2020

Since early October, Vietnam has experienced a succession of six tropical storms and typhoons which have caused extreme rainfall and brought widespread flooding to much of central Vietnam. Rainfall this year has been exceptional, with many areas experiencing record-breaking precipitation levels. For example, Hue in Thua Thien-Hue Province has received 2,336mm of rainfall since the start of October. In comparison, the city usually receives 2,798mm of rainfall across the entire year and only 757mm in the month of October (AccuWeather , 2020).

Quang Tri, Thua Thien-Hue, and Quang Binh provinces have seen the greatest impacts from the storms. As of 11 November 2020, reports confirmed at least 235 deaths and missing people with 390,000 houses inundated (VNExpress, 2020).

JBA’s Event Response team has analysed the impacts of these storms and carried out rainfall probability analysis for Tropical Storm Linfa, Tropical Storm Nangka, Tropical Goni and Storm Etau, as well as comparing the flooding against our Vietnam flood maps and Global Flood Model (get in touch for more information on these).

Figure 1: Rainfall accumulation in Vietnam from 11 October – 12 November 2020. (Source: NASA PPM, 2020; processed by JBA Risk Management)

Tropical Storm Linfa

Linfa made landfall in the central region of Vietnam on 11 October in Quang Nam and Quang Ngai provinces and continued to bring heavy rainfall on 12 October to central provinces; within 24 hours, Ta Long (Quang Tri province) saw 210mm of rain and Quang Dien (Thua Thien-Hue province) received 182mm of rain (ReliefWeb, 2020a). For the period 5 October 2020 to 13 October 2020, the Vietnam Disaster Management Authority reported 8-day total rainfall ranging between 1,000 and 1,975mm (Vietnam Disaster Management Authority, 2020a). In Hue, Thua Thien-Hue province, flood depth reached approximately 0.4–1m. (The Watchers , 2020)

JBA Risk Management has compared the storm’s 8-day rainfall total with historical 8-day accumulation totals based on gridded rainfall data. The estimated return period for Tropical Storm Linfa, based on rainfall intensity, ranged from 200–900 years (Table 1).

Table 1: Rainfall return period analysis for locations with high rainfall - 05 October 2020 (19:00hr) to 13 October 2020 (19:00hr). (Data source: Vietnam Disaster Management Authority, 2020; Physical Sciences Laboratory NOAA, 2020)

The storm resulted in 110,000 houses being inundated, with 382 completely destroyed (ReliefWeb, 2020a). The agriculture industry in Vietnam was badly hit, with 9,772 hectares of rice, crops and aquatic farm produce destroyed by the deluge (ReliefWeb, 2020a). As of 17 October, 61 deaths had been reported following Linfa (Lao Dong , 2020).

Tropical Storm Nangka

Tropical Storm Linfa was followed in quick succession by Tropical Storm Nangka which hit the Vietnam coast on 13 October in the Thai Binh and Thanh Hoa provinces. From 13 October to 16 October the three-day rainfall total reached 298–411mm at various locations (Table 2). JBA’s analysis against the historical 3-day record estimates that the rainfall intensity has an estimated return period of 50 to 220 years (Table 2).

Table 2: Rainfall return period analysis for locations with high rainfall - 13 October 2020 (19:00hr) to 16 October 2020 (19:00hr). (Data source: Vietnam Disaster Management Authority, 2020; Physical Sciences Laboratory, NOAA, 2020)

Around 150,000 people were evacuated during Tropical Storm Nangka and the total death toll from 6 October 2020 to 17 October 2020 reached 64 in Vietnam (Vietnam Disaster Management Authority, 2020b).

Tropical Storm Saudel

On 25 October, Tropical Storm Saudel brought waves of 3m high along the Vietnam coast between Quang Tri and Thua Thien-Hue provinces causing significant flooding. The worst affected provinces include Ha Ting, Quang Binh, Quang Tri and Thua Thien-Hue. As of 22 October, a total of 114 deaths and 21 missing people were reported (Garda , 2020).

Figure 2: Loc Thuy Commune in Le Thuy District, Quang Binh Province is one of the most heavily flooded areas in the central region (Source VNExpress).

Typhoon Molave

Typhoon Molave made landfall on 28 October near Quang Ngai as a category 2 storm – the fourth cyclone system to reach the east coast of Vietnam in October 2020. Molave was also reported to be the strongest storm to hit Vietnam in the last 20 years. From 28 October to 29 October, rainfall ranged between 150-400mm in Hue-Phu Yen and Central Highlands and between 500-700mm in South Nghe Anh and Ha Thin (ReliefWeb, 2020b). In Hoi An, flood waters reached a depth of 0.5m (VnExpress , 2020a). Wind speeds were reported to have peaked at 150kph, while waves reached heights of 6-8m along the coast (VNexpress, 2020b).

Approximately 1.3 million people were evacuated prior to the arrival of the storm (Reuters, 2020). Around 92,000 houses were damaged, 96.5% of which were located in Quang Nam, and at least 5,000 houses were destroyed completely. The estimated loss to property damage is between USD$430 million and USD$1 billion (Bloomberg , 2020; SCMP, 2020 ). Landslides in Quang Nam province caused 15 deaths and 40 people were reported missing. Typhoon Molave hit the Philippines prior to arrival in Vietnam, with 16 deaths reported. In addition, 175,000 families were affected with 44 deaths reported in Cambodia (ReliefWeb, 2020b).

Figure 3: Flooding in Ha Tinh, Vietnam following Typhoon Molave, dated 1 Nov 2020 (Source: Vietnam National Centre for Hydro-Metrological Forecasting, 2020).

Tropical Storm Goni

The weakened Typhoon Goni that devastated the Philippines made landfall on Vietnam on 6 November 2020. The tropical depression, which first hit Binh Dinh province, brought high rainfall to several central provinces such as Quang Ngai, Phy Yen and Knanh Hoa, as well as inBinh Dinh itself (ReliefWeb, 2020a). Storm Goni is the fifth tropical cyclone and flood event to hit Vietnam since October 2020, where most of the country’s regions are still battling with the aftermath of previous disaster events. Between 5 November and 6 November, affected regions experienced heavy to torrential rainfalls; Binh Dinh and Quang Ngai provinces received significant rainfall of between 100 and 200mm, with some areas receiving more than 300mm. For example, Duc Phong, Pho Phong and Duc Phu (Quang Ngai province) at 315mm, 305mm and 265mm respectively, as well as An Tin and Hoai Son (Binh Dinh) at 212mm and 165mm respectively (ReliefWeb, 2020b). JBA’s analysis against historical records estimates the rainfall brought by Storm Goni sits at an intensity with return periods between 3 to 50-years (Table 3).

Table 3: Return period analysis for locations with high rainfall reported due to Tropical Storm Goni (Rainfall data: ReliefWeb, 2020b). 

Due to the significant rainfall brought by Goni, more than 13,000 people were evacuated over the provinces as river flood warning levels raised to classes 2- 3 (Relief Web, 2020a; ReliefWeb, 2020b). Goni, which struck Vietnam a week after the catastrophic Typhoon Molave, had given victims no time for recovery. By the time Goni struck, there had been around 130 deaths with an estimated 170,000 livelihoods having been disrupted (ReliefWeb, 2020c).

Storm Etau

On November 10, Storm Etau became the twelfth storm to hit Vietnam and the sixth flood event to reach Hoi An in central Vietnam (Garda, 2020). Even after the storm had passed, coastal cities like Vinh Thanh and Vinh Phuong, and towns in Nha Trang were inundated, with floods of about 0.5 – 1m (Newsbeezer, 2020). Streets in Hoi An, a town in Quang Nam province, had floods up to 1m deep along several streets (VN Express, 11 Nov). Hoi An town is an ancient town popular with tourists and lies on the coast of Vietnam; it hosts many coastal beach resorts. Based on the return period analysis for Hoi An Town, the 24-hour rainfall total of 250-350mm has an estimated return period of 10 to 110-years (Table 4; VN Express, 2020; Garda, 2020). La Hai town, located in the mountainous region of Dong Xuan district in Phu Yen province, saw flood depths of 1 - 2.5m (Vietnam Investment Review, 2020).

In the central provinces, Binh Dinh, Khanh Hoa and Phu Yen received rainfall of about 250mm (Garda, 2020) while some locations in Quang Nam province received rainfall of up to 350mm between 10 November and 11 November (VN Express, 11 Nov).

Table 4: Return period analysis for locations with high rainfall reported due to tropical Storm Etau (VN Express, 2020; Garda, 2020).

Storm Etau resulted in two deaths and caused 371 houses to collapse as of 11 November. (ReliefWeb, 2020d).

JBA’s Event Response team has compared the areas reported to be flooded following the storms to JBA’s Vietnam Flood Maps.

Figure 4: False colour image of observed flooding 22 October 2020 Kien Giang River, Le Thuy, Quang Binh Province, captured by Sentinel-2 L2A (top) compared to JBA’s 1-in-50-year flood map at 30m resolution (Copernicus Sentinel data 2020 processed by Sentinel Hub).

Figure 5: False colour image of observed flooding 22 October 2020 Gianh River, Quảng Trạch District, Quang Binh Province, Vietnam, captured by Sentinel-2 L2A compared to JBA’s 1-in-50-year flood map at 30m resolution (Copernicus Sentinel data 2020 processed by Sentinel Hub).

Outlook

Based on a World Bank report, an estimated 11.8 million people located in Vietnam’s coastal provinces are at risk of flooding with 35% of the population located close to vulnerable and overpopulated coastlines (Retuers, 2020). Analysis from JBA’s Global Flood Model indicates that 2.1 million people are annually exposed to flooding in Vietnam. Vietnam’s Average Annual Loss is 0.4% of GDP, making Vietnam the fifth most exposed country to flood globally and second most exposed in South-East Asia. Residential insurance penetration remains low, whilst the fact that over 60% of industrial parks are within the 1-in-50-year flood extent is also cause for concern. As economic losses rise and the insurance gap narrows, without considered flood risk management, insured losses seem likely to follow.


JBA Risk Management has nationwide return period flood maps for Vietnam 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

AccuWeather. 2020. Tropical Storm Saudel threatens to unleash more rain across flood-weary Vietnam. [online] Available at: https://www.accuweather.com/en/hurricane/tropical-storm-saudel-threatens-to-unleash-more-rain-across-flood-weary-vietnam/835156

Bloomberg. 2020. Vietnam estimates typhoon Molave caused USD430 million of damage. [online] Available at: https://www.bloomberg.com/news/articles/2020-11-01/vietnam-estimates-typhoon-molave-caused-430-million-of-damage

Garda. 2020a. Vietnam: Flooding casualties mount as Typhoon Saudel approaches October 2020/update 4. [online] Available at: https://www.garda.com/crisis24/news-alerts/391831/vietnam-flooding-casualties-mount-as-typhoon-saudel-approaches-october-22-update-4

Garda. 2020b. Vietnam: Tropical Storm Etau makes landfall north of Nha Trang (Khanh Hoa province) November 10 /update 2. [online] Available at: https://www.garda.com/crisis24/news-alerts/398246/vietnam-tropical-storm-etau-makes-landfall-north-of-nha-trang-khanh-hoa-province-november-10-update-2

Lao Dong. 2020. Rain and flood in the Central region: 61 people died, warning from landslides and flash floods. [online] Available at: https://laodong.vn/xa-hoi/mua-lu-tai-mien-trung-61-nguoi-thiet-mang-canh-bao-sat-lo-va-lu-quet-846091.ldo

Physical Sciences Laboratory NOAA. 2020. CPC Global Unified Precipitation data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA. [online] Available at: https://psl.noaa.gov/
ReliefWeb. 2020a. Flash Update 03 14 October 2020 Tropical Storm Linfa & Nangka. [online] Available at: https://reliefweb.int/sites/reliefweb.int/files/resources/FlashUpdate_03_14Oct2020-TS-LINFA-NANGKA-MEKONG.pdf

ReliefWeb. 2020b. Typhoon Molave – Oct 2020. [online] Available at: https://reliefweb.int/disaster/fl-2020-000211-vnm

ReliefWeb. 2020a. Vietnam, Philippines - Typhoon GONI update. [online] Available at: https://reliefweb.int/report/viet-nam/vietnam-philippines-typhoon-goni-update-gdacs-jtwc-ndrrmc-government-vietnam-echo

ReliefWeb. 2020b. Flash Report on Natural Disaster Risk Management on November 5, 2020. [online] Available at: https://reliefweb.int/report/viet-nam/flash-report-natural-disaster-risk-management-november-5-2020

ReliefWeb. 2020c. Switzerland provides humanitarian assistance to the victims of the floods in Central Vietnam. [online] Available at: https://reliefweb.int/report/viet-nam/switzerland-provides-humanitarian-assistance-victims-floods-central-vietnam

ReliefWeb. 2020d. Vietnam, Cambodia, Thailand - Tropical Depression ETAU update. [online] Available at: https://reliefweb.int/report/viet-nam/vietnam-cambodia-thailand-tropical-depression-etau-update-dg-echo-gdacs-jtwc

Reuters. 2020. Vietnam ready to evacuate 1.3 million people as typhoon approaches. [online] Available at: https://www.reuters.com/article/us-asia-storm-idUSKBN27B0FV

SCMP. 2020. Typhoon Molave smashes through central Vietnam, leaving floods and despair in its wake. [online] Available at: https://www.scmp.com/week-asia/health-environment/article/3107478/hammered-typhoon-molave-people-vietnam-struggle-stay

The Watchers. 2020. Death toll climbs to 29, over 130 000 houses flooded in central Vietnam. [online] Available at: https://watchers.news/2020/10/13/vietnam-floods-death-toll-october-2020/

Vietnam Disaster Management Authority. 2020a. Quick report on the work on duty prevention and control on October 14, 2020. [online] Available at: https://translate.google.com/translate?sl=vi&tl=en&u=http://phongchongthientai.mard.gov.vn/Pages/bao-cao-nhanh-cong-tac-truc-ban-pctt-ngay-14-10-2020.aspx

Vietnam Disaster Management Authority. 2020b. Quick report on the work on duty prevention and control on 17 October 2020. [online] Available at: http://phongchongthientai.mard.gov.vn/Pages/bao-cao-nhanh-cong-tac-truc-ban-pctt-ngay-18-10-2020.aspx

Vietnam National Centre for Hydro-Metrological Forecasting. 2020. News on Rivers in Nghe An, Ha Tinh. [online] Available at: https://kttv.gov.vn/Kttvsite/vi-VN/1/tin-lu-tren-cac-song-o-nghe-an-ha-tinh-post17978.html

VnExpress. 2020a. Storm Molvane, mightiest in 20 years, makes landfall over central Vietnam. [online] Available at: https://e.vnexpress.net/news/news/storm-molave-mightiest-in-20-years-makes-landfall-over-central-vietnam-4183361.html

VnExpress. 2020b. The destructive force of Vietnam’s biggest storm in 20 years. [online] Available at: https://e.vnexpress.net/news/video/the-destructive-force-of-vietnam-s-biggest-storm-in-20-years-4183485.html

VN Express. 2020c. Quang Binh left desolate in wake of receding floods. [online] Available at: https://e.vnexpress.net/photo/news/quang-binh-left-desolate-in-wake-of-receding-floods-4182258.html

VN Express. 2020d. Hoi An suffers deluge following more heavy rains. [online] Available at: https://e.vnexpress.net/news/news/hoi-an-suffers-deluge-following-more-heavy-rains-4190177.html
Vietnam Investment Review. 2020. Storm Etau claims two lives in central region. [online] Available at: https://www.vir.com.vn/storm-etau-claims-two-lives-in-central-region-80667.html

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