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Low river levels caused by extreme low rainfall


The following is an op-ed written by Jeremy Bird, CEO of the Mekong River Commission, which appeared in the Bangkok Post, 16 March 2010


As readers of this paper will know, much of northern Thailand and Lao PDR, southwest China, and some parts of Viet Nam are in the grips of one of the worst dry periods in recent history. This is reflected in unusually low river levels throughout the Mekong basin as well as in other major rivers such as the Red River in northern Viet Nam.

The implications of this, as recent media reports have correctly pointed out, are serious. Many people in this region already face poverty. Difficulties in access to water makes livelihoods from farming and fishing more precarious for affected communities and raises the risk of disease from use of polluted sources. Low water levels have also severely disrupted river transport both for trade and tourism, further affecting livelihoods of people who depend upon the river.

Analysis of the Mekong River Commission’s data reveals that the low water levels in the Mekong and its tributaries are the result of extreme natural conditions. Very low rainfall this dry season, following a particularly early end to the wet season in 2009, has led to river levels below those seen in at least 50 years.

For example, at Chiang Saen in northern Thailand close to the Chinese border, the 2009 wet season ended about one and a half months early and rainfall in both September and October 2009 was more than 30 percent less than average. Rainfall in Yunan province has also been low, with amounts consistently below average since August 2009.

The reduced Mekong levels at the end of the wet season were typically at one-in-ten year lows. Coupled with very low rainfall afterwards, this means that levels at most mainstream measuring stations in Lao PDR and Thailand dropped below those for the 1992-1993 season, then the most extreme dry period on record. It is important to note that the conditions became more severe moving downstream from Chiang Saen to Vientiane.

Now let us consider the situation in the tributary rivers which are what feeds into and contribute to the flow in the mainstream. For example, flow in tributaries in northern Lao PDR such as the Nam Ou, north of Luang Prabang, are the lowest since our records began 50 years ago. These are natural conditions.

Where hydroelectric dams have been constructed, such as on the Nam Ngum, flows downstream tend to be higher as water stored in the wet season is released for hydroelectricity production in the dry season.

In Thailand, many media reports place the blame for low Mekong levels on the mainstream Chinese hydropower schemes and yet they operate in the same way, to store water during the wet season that can be used during the dry season. In the next few years, the completed storage capacity of the Chinese dams will lead to increased dry season flows downstream, perhaps as much as 40 percent more in Vientiane. At the moment however those projects that have been completed are not sufficiently large to consistently deliver such benefits.

We are all aware of the negative effects that dams can bring on natural resources and the livelihoods of people that depend upon them. They have been widely reported in the media, by independent commissions, project evaluation studies and community experience. But this should not be translated into a view that all problems can be attributed to dams. The natural Mekong river system is incredibly variable from year to year as the long history of floods and drought demonstrates.

There appear to be two main questions to ask in relation to upstream dams. First, did they in anyway reduce levels below natural conditions? The underlying trend of flow recorded at Chiang Saen for the period from the end of the wet season 2009 indicates a similar pattern to previous dry years although with a more extreme slope due to the very low rainfall conditions. In early to mid January, there was an increase above this trend due to hydropower generation upstream which had the effect of delaying the onset of the extreme low flow conditions. However, limited storage upstream appears to have been a constraint to further supplementing low river flows.

Secondly, the question is whether there is any scope for release of water stored upstream from last year’s wet season to raise the historically low water levels? This is where further information and discussion is required, but it is important to note that China also has a common interest in raising water levels if it can to alleviate the problems being faced on its river trade route through to northern Thailand. Low volumes of reservoir storage may currently provide little opportunity to act in this way.

More research needs to be done. The Mekong River Commission is engaging with China to better understand how dams and other human activities on the river impact on those downstream, as well as to model future changes, including the potential impact of climate change. A team of MRC modellers will be working with Chinese counterparts over the next weeks to exchange information and better analyze and understand both the current situation and longer term changes. These include increased dry season flow due to dam operation and the prospects for more extremes of flood and drought.

The current low flow conditions are expected to continue through April and it is an issue that affects the tributaries of the Mekong as much, if not more, than the mainstream. There are certainly steps that can be taken in terms of conserving water and extending intake pipelines at water supply schemes so that they can use the water still available in the river. Countries of the region are not as familiar with drought management as with flood preparedness. Yet, with climate change effects likely to intensify both flooding and drought over coming years, it is an area where considerable attention is needed both at policy and practical levels.


By Jeremy Bird, CEO, Mekong River Commission



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