An all-too-familiar sight

While a repeat of the 2011 floods is unlikely, heavy rains pose a threat to rice cultivation and will not mitigate drought next year

Locals brave the flood that recently hit the Bang Bo district of Samut Prakan province. Photos: Somchai Poomlard

Torrential rain has recently left many areas underwater. Last month, it caused flash flooding and forest runoff in the northern provinces. Caught off guard, residents climbed onto rooftops as water swept into their properties.

Downpours have also continued to pound roads and communities in Pattaya, leading to the worst flooding in a decade. Rains inundated an industrial park -- the Bang Poo Industrial Estate suffered a loss of 900 million baht -- and neighbouring areas in Samut Prakan.

Compounded by a tropical storm, heavy rain has persisted in many provinces, evoking tragic memories of the flooding in 2011. The national crisis submerged factories and farmlands, killed over 800 people, and caused over 1.4 trillion baht in damage.

Will Thailand be wreaked by huge floods just like in 2011? Recently joining a forum held by the National Research Council of Thailand, experts dismissed the possibility of an epic deluge but predicted that the country remains at risk of flooding and drought next year.

Locals brave the flood that recently hit the Bang Bo district of Samut Prakan province. Photos: Somchai Poomlard

Epic inundation unlikely

Assoc Prof Seree Supratid, director of the Climate Change and Disaster Centre of Rangsit University, said the chance of epic floods is less than 10% but his model shows each region having different probabilities of flooding events -- Central (10%-20%), Northeast (20%-40%), East (30%-40%), and South (50%-60%).

"But what if a megaflood occurs? We can't wait for the infrastructure project [on the Chao Phraya River basin] which is due to be completed in the next decade. We must be prepared. The command centre must predict which communities are most likely to feel the impact and forward the information to provincial authorities," he said.

Former Bangkok governor Bhichit Rattakul and now president of the Thai Network for Disaster Resilience said flooding in the capital is likely to occur from two sources -- upstream water and rain -- and that it can be solved by release and diversion.

"The city will flood if maintenance work falls behind and there is an impact of climate change. For example, the amount of rain this August was higher than the same month last year," he said.

The Bangkok Metropolitan Administration has used the pipe jacking technique to increase water storage capacity, constructed water tunnels, expanded river dykes, and built monkey cheek areas and water banks. It is also working with the Royal Irrigation Department to regulate the amount of upstream water.

Too much, then too little

Sutat Weesakul, the director of the Hydro-Informatics Institute, said that after light rainfall for eight months, the country is expected to experience heavy downpours from September-November, resulting from a monsoon trough and strong southwest monsoon winds. Another storm is expected to hit the country later this month, which may cause flooding in cities, districts and riversides.

"Heavy rainfall means high water levels in dams such as the Mae Mok [in Lampang], the Lam Pra Plerng [in Nakhon Ratchasima], and the Naruebodindrachinta [in Prachin Buri]. The Bhumibol dam [in Tak] and Sirikit dam [in Uttaradit] will also be able to collect additional water," he said.

The data, however, shows that this year's total rainfall and water intake at dams is only 945 millimetres (mm) and 17,208 million cubic metres (mcm), lower than the figure of the floods in 2011 when rainfall and dam water intake totalled 1,824mm and 72,143mcm.

Sutat said the dry season has caused the amount of usable water in the four major dams to drop from 5,771mcm on Nov 1 last year to 2,263mcm on April 30. However, the rainy season has increased the volume of usable water from 2,265mcm on May 1 to 3,108mcm on Sept 15.

"However, there should be at least 8,000mcm of usable water by Nov 1 for off-season rice farming next year. But this is unlikely," he said.

The data indicates that four main reservoirs hold 9,804mcm of water in total, which is lower than the figure of 22,336mcm in 2011. Sutat stressed that "they are unlikely to cause flooding" because this year's water volume is close to the figure of 8,917mcm seen in 2015, which led to a severe drought.

Locals brave the flood that recently hit the Bang Bo district of Samut Prakan province. Photos: Somchai Poomlard

Calculating financial loss

Asst Prof Pongsak Suttinon, a lecturer at Chulalongkorn University's Faculty of Engineering, made a risk assessment of financial loss due to submerged rice. Flooding is likely to occur in the Central Region (the Chao Phraya River basin) and some parts of the Northeast.

"In the worst-case scenario, financial loss will total 13 billion baht in September, followed by 11 billion baht in October, 2.3 billion baht in November, and 55 million baht in December," he said.

However, Pongsak added that the data shows that the amount of water in four main dams has dropped for three consecutive years, and this will increase the chance of drought and affect rice cultivation. In fact, off-season rice growing has exceeded the amount of water available for 20 years.

"With poor water management systems and lack of storms bringing water to reservoirs, the financial loss caused by drought will be 15 billion to 20 billion baht next year. This is equal to Mae Hong Son's gross domestic product," he said.

Putting plans in place

Thanet Somboon, an expert in hydrology at the Royal Irrigation Department, said its management involves collecting, delaying and releasing water from upstream to downstream.

"Currently, four main dams hold 3,200mcm of usable water. They are capable of collecting additional water but we must watch out for rain and tidal bore," he said.

The agency has put in place water management measures. While the Bangrakam lowland area (upper Chao Phraya River basin) can collect 400mcm, 12 lowland areas (lower Chao Phraya River basin) can hold 1,500mcm.

Other measures involve water management in the east and the west of the Chao Phraya River. One of them is the drainage system of the Klong Mahachai-Klong Sanamchai monkey cheek project. At the bottom of the water management system are canal floodgates. Authorities have also installed water pumping machines along rivers.

When asked about drought, he used the risk map to predict that the four major dams will be able to hold 4,500-5,200mcm of usable water next year. Therefore, the agency will manage water in order of priority, namely for urban consumption and then for agricultural, industrial and other activities.

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