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 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. And what is the situation now?

Bhumibol Dam

Safari

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 or so (no idea why!), but it goes from January to December. “Full” data is only available for these 8 years.

BP: So down from 91% full to 60% and now 46% which is right on track. At the same time last year, capacity was 58%. There is plenty of capacity for excess rainfall and you will see unlike last year, the % of water in the dam during the beginning of the rainy season has plateaued instead of going upwards. This suggests they are correctly managing the level of water in the dams (for now at least).

Sirikit Dam

Safari

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: So in 2012 down from 89% full to 60% and now 44%. At the same time last year, capacity was 65%. Unlike in 2011, the level of water going into the dams is still continuing to drop. 44% is also the second lowest % of stored water in the Sirikit dam compared with the other 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 10,934 million cu/m as of July 3 or 44%. This compares to 14,833 million cu/m or 60% at the same time last year. This information comes from the Royal Irrigation Department. 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.

BP thinks the chances of severe flooding causing as much economic damage and the loss of lives as 2011 is quite low.

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:

Source: Met Dept

Now, how does this compare to 2012? To be honest, finding the right charts is difficult and so the below charts provide too many details. The below chart is from May 2011:

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Source: Met Dept

Then, for 2012:

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Source : Met Dept

NOTE: May 2012 stats were not released until June 19 and the June 2012 stats have not been released yet so we only have up until the end of May 2012.

BP: As you can see for the North, we have 35% above normal or an extra 99.9m of accumulated rainfall so far up until the end of May 2012, but this compares to 71% or an extra 200.2m of accumulated rainfall at the same time in 2011.

Google Chrome

Source: Met Dept
Google Chrome

Source : Met Dept

BP: As you can see, we have -8% less rainfall than normal or -21.5mn less accumulated rainfall so far up until the end of May 2012. This compares to 70% or an extra 198.5.m of accumulated rainfall at the same time in 2011.

So far this year, we just haven’t had as much rain as 2011. Last year, by the end of May it was evident that we were going to be getting a significant amount of extra rain – see the May 2011 chart above to see how much above normal rainfall. As of the end of May 2012, we are not even close to the excess rain of 2011 in the North. In the Central Region, we have even had less rain than normal. Of course, this is only up until the end of May and we still have most of the rainy season to go so it is impossible to say with certainty until the rain actually falls how much above normal rainfall we will have and how the government will manage the dams. Nevertheless, we can do some analysis based on what we know so far and forecasts of rainfall:

In the below image, for 2011 you have the actual levels of rainfall in the North and Central Regions. The 2012 figures are from the Meteorological Department and is their prediction on rain over the rainy season. Both figures are in mm:
Microsoft Excel

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

 BP: 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.