Mekong River Commission


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5. The 2008 flood season

5.3 Temporal aspects of the 2008 Mekong flood season

Defining as usual, the onset of the flood season as the first sustained 'up-crossing' of the mean annual discharge and its end as the last 'down-crossing' the figures in Table 5.2 indicate that in the middle reaches, at Vientiane and Pakse the 2008 seasonal onset was two to three weeks early. Elsewhere, the timing of the start was 'normal' while throughout the Basin the season ended just two weeks later than average.

Table 5.2 Start and end dates of the 2008 flood season compared to their historical mean and standard deviation at selected mainstream locations.
Site Onset of flood season End of flood season
  Historical average Standard Deviation 2008 Historical average Standard Deviation 2008
Chiang Saen 28th June 13 days 27th June 14th Nov 14 days 22nd Nov
Vientiane
3rd May
14 days
15th June
11th Nov
15 days
21st Nov
Pakse
29th June
16 days
9th June
5th Nov
11 days 20th Nov
Kratie
1st June
16 days
5th July
7th Nov
12 days
20th Nov
Note: Levels for Vientiane were recorded at the river gauge at Kilometre 4.

The importance of employing a meaningful definition of the onset and end dates of the flood season was amply demonstrated in 2007. Then the onset of flood season conditions in the latter part of July and the first week of August was the latest observed in the last 80 to 90 years. As a consequence the low water levels observed during most of July were unprecedented and had negative impacts upon the environment, fisheries, agriculture and navigation.

 




 


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