What are the chances of severe flooding in Thailand in 2012? Late August 2012 version
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What are the chances of severe flooding in Thailand in 2012? Late August 2012 version

Early last month, BP blogged on the chances of severe flooding in 2012 and stated:

BP will check again at the end of August/beginning of September as by this time, the quantity of water in the dams should have risen significantly and we will have an ever better idea on the management of water levels in the dams, but even by now we can make some tentative predictions.

Even assuming the worst-case scenario, it is not as much rain as 2011. It is not impossible we will have more rain in 2012, but there are no signs either in the first 5 months of this year or the forecast to expect suddenly for the rain to reach a new record high over the next 5 months.

In addition, we still have more capacity in the dams to take on additional water so even in the worse-case scenario this won’t necessitate the panicked release of large quantities of water in September and October 2011. We can have discharges of water from the dams earlier in July-August, in particular, to reduce the level of intake into the dams.  Looking at all the data, there is no evidence to suggest we will have a severe flood like 2012 or even a flood approaching that level. BP will look again at the end of August/beginning of September for an update.

BP: Now, this post is an updated version of that July post.

Last year, as Thailand experienced severe flooding, BP blogged repeatedly about the the water level in dams – see Sirikit and Bhumibol dam posts. The relevance being as the water level in the dams increased, the authorities had to release water from the dams, but this was happening during the rainy reason when there was excess rainfall – see posts here and here. In BP’s opinion, the combination of extra rain and the mismanagement of the dam levels (although see this post for a contrary opinion on mismanagement of dam levels) caused the floods last year. The government can’t do anything about rainfall, but it can manage the water in dams differently.

There was some anxiety expressed in January that the water level in the dams was too high and not much was being done about it although as BP noted in this post, the extent of downward trajectory of the dam levels suggested the panic was overblown. Back in early January, Bhumibol dam was 91% full and the Sirikit dam was 89% full. Then, in March, BP blogged again at the end of March that the quantity of water in those two dams, the two largest dams, had reduced to 60% and the plan was to reduce the the water level in those dams to be 45% full in order that, if necessary, there was additional capacity in the dams in case there is excess rainfall during the rainy season. Then, in early July, Bhumibol dam was 46% full and the Sirikit dam was 44% full. And what is the situation as of late August?

Bhumibol Dam

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Source: Hydro and Agro Informatics Institute (an agency under Ministry of Science and Technology) although it states the figures are from the Irrigation Department.

Note: Left-hand vertical axis is million cubic metres. Horizontal axis is date. It is every 31 days or so (no idea why!), but it goes from January to December. “Full” data is only available for these 8 years.

BP: You can see from the above chart that there is a lot of excess capacity compared to last year, but exactly how much? Now, the amount of water in the dams is at 48% which compares very favourably with 75% at the same time last year. There is plenty of capacity to absorb excess rainfall.

Sirikit Dam

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Source: Hydro and Agro Informatics Institute (an agency under Ministry of Science and Technology) although it states the figures are from the Irrigation Department.

Note: Left-hand vertical axis is million cubic metres. Horizontal axis is date. It is every 30 days (no idea why!), but it goes from January to December. “Full” data is only available for these 8 years.

BP:  You can see from the above chart that there is a lot of excess capacity compared to last year, but exactly how much? Now, the amount of water in the dams is at 53% which compares very favourably with 93% at the same time last year. Unlike in 2011, the level of water going into the dams is  only starting to rise now and slowly compared to previous years. 53% is also the second lowest % of stored water in the Sirikit dam compared with the previous 7 years.

The Sirikit and Bhumibol dams are the two biggest dams in the North, but there are a few other smaller dams. For all the dams in the North, the quanity of the water in the dams is 11,993 million cu/m as of August 25 or 49%. This compares to 20,320 million cu/m or 82% at the same time last year. This information comes from the Royal Irrigation Department.  There is capacity for an extra 8,000 million cu/m of water to enter the dams in the North compared to the same time last year.

What about rainfall? First, rainfall up until end of October 2011 was 28% above normal on a nationwide basis, 42% in the North and 26% above normal from the Central Region (source: Met Dept). The reason for highlighting the North is that is where the two major dams, Sirikit and Bhumibol most relevant to flooding, and major rivers which flow down to the Central Region are located. For the Central region, well lets be honest, it is because Bangkok and the surrounding provinces flooded that made the floods in 2011 an economic and political issue. Water from the North flows down into the Central Region and well if there is less rain in the Central Region less water needs to be released from other dams in the Central Region and will get into the rivers etc.

Ok, the extra rainfall in 2011 may not sound a lot, but looking at Meteorological Department figures from 1951 onwards you can see that for the full year of 2011 it is the highest above normal rainfall listed recorded ever. This just shows how much above normal the level of rainfall was last year. The chart is below:

mean_annual_rainfall_normal

Source: Met Dept

Now, how does this compare to 2012?

The below chart is from July 2011 for Northern Thailand:
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Source:  It is from the Met Department. The Met Dept have removed the older monthly summaries from their site with the earliest being from September 2011 so don’t have a link (had already downloaded it from last year)

Then, for 2012, for Northern Thailand:

 

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Source : Met Dept

NOTE: End of July 2012 stats are the latest available

BP: As you can see for the North, rainfall for the first seven months of 2012 is only 13% above normal compared to 56% above normal for the first seven months of 2011. There just isn’t excess rainfall that has swelled the rivers and will be flowing into the dams in such volume that it will be a problem like last year.

For Central Thailand:
7865630158_64e7871c6d_o

Source:  It is from the Met Department. The Met Dept have removed the older monthly summaries from their site with the earliest being from September 2011 so don’t have a link (had already downloaded it from last year)

7865632010_c23326f331_o

Source : Met Dept

BP: As you can see for the Central region, rainfall for the first seven months of 2012 is only 5% above normal compared to 50% above normal for the first seven months of 2011.

So far this year, we just haven’t had as much rain as 2011. Last year, by the end of July it was evident that we were going to be getting a significant amount of extra rain – see the July 2011 charts above to see how much above normal rainfall. As of the end of July2012, we are not even close to the same quantity of excess rain as 2011 in the North or in the Central Region.

What about the forecast for additional rain for the rest of the year?

In the below image, for 2011 you have the actual levels of rainfall in the North and Central Regions. The 2012 prediction figures are from the Meteorological Department and is their prediction on rain over the rainy season. Then to see how the Met. Department has done so far in their prediction, BP has included the actual rainfall figures for June and July 2012. All figures are in mm:

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Source:  For 2011, June (PDF), July (PDF), August (PDF), September (PDF), and October (PDF). For 2012 predictions, see this file (PDF). For actual 2012 rainfall, see June (PDF) and July (PDF).

BP: The rainfall in July 2012 for the Central Region  exceeded the worst-case scenario, but for the North and for both regions in June it hasn’t. In fact, in June it was was below the prediction. Of course, this suggests the weather is unpredictable, but it also means it has been up and down. For there to even have any possibility of a severe flood, there has to be consistently above normal rainfall so far. There just hasn’t been.

CONCLUSION: We still have more capacity in the dams to take on additional water so even in the worse-case scenario this won’t necessitate the panicked release of large quantities of water in September and October like we had last year. Rainfall is only slightly above normal so far this year.  Looking at all the data, there is no evidence to suggest we will have a severe flood like 2011* or even a flood approaching that level.

*Corrected from 2012.

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