Will Bangkok Flood in 2021?
The short answer to your question: The Bangkok region will probably not have significantly more flooding in 2021 than in other years, and almost surely 2021 will not be comparable to the Great Flood of 2011.
There is a lot of talk about possible flooding of Bangkok in 2021, with images of the great flood of 2011 not far off in memory. What this article provides is analytical information showing that the situation in 2021 is not nearly as bad as it was in 2011 for Bangkok, and actually the situation is relatively good in 2021.
In some other localities in Thailand, things are different, but those are other situations.
I also cover how you can protect many homes from interior flooding. In the Thailand Great Flood of 2011, my house became embedded in a lake for weeks, to a depth of up to around 1 meter at the front door, though stayed dry inside due to sealing methods which worked, so I documented them shortly afterwards. That link is near the bottom of this page.
* Rainfall this year is not particularly high thus far, in the areas which feed the Chao Phraya River
* Most dams upstream are not very high, so they can hold more water. There are some exceptions, and water release has already started, but it floods mainly localized communities far from Bangkok along their release channels.
* Construction of flood mitigation systems after the 2011 flood should be much better able to handle the water this year.
This does not rule out the possibility of considerable flooding, given the unpredictable nature of the weather, as it's possible that multiple tropical storms could form and pass thru the key upcountry areas, but it seems quite unlikely.
Before getting into the details of the analysis, let's first cover some basics:
Of course, news sources will always sell stories of localized floods, and people may form perceptions that those images apply to wide areas of Thailand, when actually it should be clarified that they are exceptional areas.
Deep flash floods happen often in low lying places within or near hilly and mountainous areas. In relatively flat places, floods between ankle and knee deep can quickly occur after heavy rainfall due to small variations in local elevations, but typically clear in hours to a day for places such as central Bangkok and many of its suburbs, due to drainage and pumping.
However, flooding of a wide region such as the Bangkok greater metropolitan area to a significant depth, and which persists, is due to water runoff from the north.
The Bangkok region is a vast sedimentary flood plain downstream of a major river, which naturally floods to some extent every year, usually. The Bangkok greater metropolitan area is only about half a meter to 2 meters above sea level.
In Bangkok and well beyond, manmade canals, dams, and floodwalls have channeled this water in various ways to complicate the flow in modern times, mostly in a way beneficial to the dwellings and crops of our technological species over recent centuries.
However, with global warming, we must watch out for particularly rainy seasons.
The rain which affects the Chao Phraya River comes from the north-northwest. Rain in the northeast (Isaan) generally drains to the Mekong River, not the Chao Phraya River, with the southern boundary being along the Korat Plateau uplift (starting with the Khao Yai mountain range and its related ranges to the east), and the western boundary being a roughly drawn line extending to the western boundary of the Khao Yai mountain range north of Bangkok. Notably, even though Khao Yai is near Bangkok, relatively very little of that water draining from the southern slopes drains into the Chao Phraya River. The southern slope water mainly drains into the Bang Pakong River, which is the next major river east of Bangkok. The northern facing areas drain ultimately far downstream to the Mekong River which makes up most of the eastern border of Thailand.
The rain which goes into the Chao Phraya River comes down from the north central and northwest. If you draw a line from Bangkok almost straight north to Pitsanulok and beyond, you have the approximate eastern boundary of the feed.
The Chao Phraya River starts in name where the Ping River and the Nan River meet in Nakhon Sawan.
The Ping River starts in Chiang Mai, with many tributaries. The Ping River at one point far downstream goes thru the massive Bhumibol Dam, located on the side the Mae Ping National Park near the border of Lamphun and Tak provinces.
The massive Queen Sirikit Dam is on the Nan River in Uttaradit Province. The Nan River starts in the Lao PDR, in the Luang Prabang Range.
As of the end of September, 2021, the Bhumibol and Queen Sirikit Dams were only about half full. In the Great Flood of 2011, they had been nearly full at this time.
There is a major dam right on the Chao Phraya River in Chainat, called the Chao Phraya Dam. It's not a reservoir, it's simply a dam on the river. Many warnings of river rises are due to increased water flow thru this dam. My wife's family live along a river in Ayuthaya in an area which floods nearly every year (yes, they're accustomed to it), so they keep informed of activity of the dam in Chainat.
Approximately 15 km north of the Chao Phraya Dam, the Tha Chin River branches off from the Chao Phraya River, and becomes the next major river west of Bangkok, running roughly parallel. (Branch point GPS: 15.226031, 100.079480)
Decades back, King Bhumibol proposed the "monkey's cheeks" system to further develop water management in Thailand, and it has been effective at mitigating a lot of flooding of valuable infrastructure and high population density areas.
There are countless khlongs and tributaries, some other dams with reservoirs around, plus places designated for emergency drainage. The Chao Phraya "watershed" is estimated to cover around 35% of the land area of Thailand. This includes the Tha Chin River network, but not the next major rivers to the east and west, the Bang Pakong River (which you cross when driving between Bangkok and Pattaya) to the east, and the Mae khlong to the west (coming out of Kanchanaburi and draining into the sea at Samut Songkram).
I won't go into too much detail for a short article here, but the main point is that there is a potentially good water management system, and in 2021 the situation is not particularly bad.
Further, checking rainfall in August 2021, the amount in the north was actually near normal.
Against all this, I have noticed the water being very high in the major Rangsit khlong right in front of my neighborhood, but that khlong is used to divert water around Bangkok. I would expect it to be near capacity if the government was trying to drain water ahead of time. There is a major network of flood gates. After the 2011 flood, they installed a raised cement wall along this khlong, but I have yet to see the water rise up high enough to test that wall since it was constructed.
Consider The Farmers, Too
The dams are not just built to manage floods. Dams are also built to provide water to farmers during the dry season.
Therefore, it is important that the dams not just drain all the water when they can. They actually need to keep as much water as they can, saved for the farmers.
Therefore, officials must make judgments and take risks. Hindsight is 20-20, so we should not judge too harshly in some cases, and instead should consider the outlooks at the time. In some cases of extreme localized flooding, there is an overflowing dam involved, typically in combination with a tropical storm or other source of heavy rain. Being an official responsible for dam decisions must be a very stressful job.
(It is common for frustrated people and the mass media to lash out and blame officials. Sometimes it may be justified, but often it's not and the officials have actually done a reasonably good job, all considered. Freedom of speech is very important, but so is critical thinking of your own, and not just following the herd mentality, especially on the internet where many people like to spout off opinions about topics they know little about.)
What Happened in 2011, Briefly
The year 2010 was exceptionally dry, with record low water levels in dams, which caused a lot of issues as regards farming. Officials started 2011 with the idea of increasing the water levels in dams.
However, 2011 turned out to be extremely different, with major rains starting in March. Northern Thailand received more than 3 times the average yearly rainfall in 2011. Most dams were around full capacity -- over, at, or near -- by the start of October 2011, and had no choice but to increase their rates of water discharge.
With the rain still coming, the result in 2011 was the worst flooding since 1942. I will spare you the details of that, as there are widespread reports elsewhere.
My 2011 Experience
It's the only time my neighborhood in Pathum Thani flooded, since it was constructed in 1992.
My house had water levels up the front door to a depth of a few feet for weeks. However, unlike any other houses I'm aware of, I was able to prevent water from flooding the interior of the house. I tried my own first time experimental approach, not following any other guidance, and not trying to sandbag my house like seemed to be the conventional wisdom.
I sealed around the front door with silicone, and taped a big plastic sheet (from a big bag) over the wooden door to prevent leakage thru the wood.
I plugged downstairs drains and toilet with 3 layers -- rubber lining for seal, a very flat hard item on top of the rubber, and heavy weights on top of the flat hard item.
I moved all electrical outlets from low lying areas to high lying areas, cut the wires to the low level sockets, and removed and filled in the cavities which previously held the sockets. (The way I plugged that cavity was not the best way, as I did it all in a hurry, so I'd rather you figure out the best way. My way worked but I plan to undo it and redo it someday for more permanent longterm stability against decay.)
I filled in any cracks I could find with silicone and plastic. (It is important to fill them from the outside, so that the water pressure will push the seal into the crack. If on the inside, then the water pressure will just try to push them out.)
The only way in and out of the house was thru a front window, and by boat. However, I had stocked up the house with lots and lots of water and food in advance.
It worked. There was some seepage thru cement and a toilet seal along the floor, but it was very slow and manageable, with periodic scoops and out the front window.
Fortunately, the power company and water utility did not cut off service. However, in some places they must for safety reasons, especially areas which flood more deeply. Modern breakers may give some protection, but the foresight to plan in advance is very important.
If there's a chance of a flood, then we are prepared to move some things from the downstairs floors to the tops of strong tables, move some valuable things upstairs, and drive our cars to either an empty high parking lot or else out of town.
If you choose to live in the Bangkok greater metropolitan region, then you just must accept these occasional possibilities and be prepared for floods. You must weigh the benefits vs. the risks.
I cover in much more detail, including photos, about how I protected the interior of my house against the flood waters which had risen up on my front door during the Thailand Great Flood of 2011.
My sources for the above information vary, and much of it is from Thai language websites which are difficult for me to review due to my limited Thai reading skills. However, some are notable:
For dam levels in mid September, 2021, see page 5 of the English language Weekly report for water watch during rainy season in 2021 by the Royal Irrigation Department. You'll see that most of the dams were not high, unlike this time in 2011. Many thanks to them, though I wish their website was less difficult to navigate and find things within.
For average rainfall in different regions, with comparisons to above and below normal, go to the English language page of the Thai Meterological Department and scroll down to the bottom of the page, then choose their "Monthly Weather Summary" and then details. For example, in August 2021, northern Thailand had rainfall of around 10% BELOW normal, and central Thailand only 7% above normal, as you can see starting on page 3. Good website.
There is often a significant lag between the current date and the report. In this article, I checked on October 1.
Any time tropical storms come into Thailand, there may be flash floods in low lying areas with significant variations in elevation, and problems can happen downstream from some dams which may overflow, especially smaller dams with major feeds. An overflowing dam can quickly cause a record flood.
When a local flood is broadcast in the news, it can be misinterpreted by many people in the public as indicative of the general situation in Thailand.
Also, political animals may try to spin stories for their own selfish interests, not caring about the Greater Good, just playing their games, exhibiting a dark side of our species in their behavior.
In this era of advertisement supported news and viral sharing, many articles bait readers by sensational headlines, cherry picked data and official quotes, and information left out which would put the event into better perspective overall. Many readers come away with a short and simplistic impression. Then perceptions can be parroted down the line into short term urban legends believed by herds. It is important to remind readers to engage in critical thinking towards news stories (and especially opinion comments on news stories by nonprofessionals). Many professional opinions are very good, but there is also an awful lot of rubbish on the internet ...
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