BP has already blogged about the poor water management of dams (part 1 and part 2) where a large quantity of water was released between August 1-Oct 16 2011 compared with in the months before and with the previous year, and also how Bangkok has had more rain this year. On this latter topic, New Mandala has had three posts herehere, and here. In the previous post, BP looked at the accumulated rainfall at the end of September 2011 and rainfall nationwide in the previous post.

In this post, BP will look at rainfall in Northern Thailand for this year for each month from January-September compared with the average rainfall to see when the authorities should have known or at least suspected that the rainfall for this year was above average. This is not to say something could have been done to completely prevent the floods or that the floods would not have been severe, but we don’t know how less severe the floods would have been. First some context. BP has been unable to find the mean annual rainfall for the North and when it is above-below normal in percentage:

Source: Met Dept

BP: This is only a 30 year period, and of course, is for all of Thailand whereas the data below is for the North. However, if you read in conjunction with a New Mandala post that has mean rainfall figures for a couple of provinces in the North and you will see that the above average rain this year is exceptional. The reason to look at the North as the two largest dams are located there and the water that is later discharged from the dams flows into the major rivers which flow downstream into Central Thailand.

The information below is from the Meteorological Department:

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Source: TMD

BP: So below average. Nothing to worry about.

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Source: TMD

BP: Again, below average. Although for both months, the amount of rain that usually falls is very low anyway.

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Source: TMD

BP: Need one say any more. The rainfall in March was extraordinarily above average. Look at Bhumipol Dam, in particular. It received 242.8mm which was 224.7 above average which meant the average was 18.1. By this point, people should have started to at least pay attention.
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Source: TMD

BP: Continued trend. Significantly more than average rainfall. By this point, people should have begin to seriously worry above earlier predictions of a drought.

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Source: TMD

BP: Another month with significantly above, average rainfall. If you thought the first 2 months were an anomaly, surely you should be worrying now. Rainfall is 71% above the norm.

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Source: TMD

BP: Again, significantly more rain for the fourth month. For the Bhumibol dam, it is 96% above the norm – nevertheless, from what BP understands other water can flow into the dam.

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Source: TMD

BP: Ditto.

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Source: TMD

BP: So the above average rain is starting to decrease.

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Source: TMD

BP:  The end result is so far that rainfall is 46% above average, but this above average rainfall didn’t just start in the last couple of months. It started in March. If not by May then June, then there should have been concern about the above normal rainfall and what was going to be done regarding the discharge of water from the dams and how increased discharge of water during the peak of the rainy season that this would exacerbate the floods.

One of the next posts that BP wants to look at is the amount of water entering the major dams. Each of these posts is part of a jigsaw puzzle.