Update for July 22-28
Notable changes on the Mekong in the last week.
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SPOTLIGHT
The Mekong Flood pulse is better than this time last year, but still below normal
In recent weeks the Mekong’s mighty flood pulse has expanded
significantly, but it is still below normal bounds for this time of
year. The image shows the current extent of seasonal flooding (blue)
compared to normal (green). Currently there are 10,360 square kilometers
of seasonal flooding, which is more than the 9,300 square kilometers
observed last year in late July but lower than the normal flood range
for this time of year from 10,800-19,900 square kilometers. The
flood pulse is the key element which makes the Mekong the world’s largest
freshwater fishery, responsible for around 20% of the global freshwater
fish catch.
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IMAGE OF THE WEEK
Significant restrictions in Vietnam’s largest Mekong Dams
The images below show the Yali Falls and Plei Krong dams, Vietnam’s
largest on the Sesan River (a major tributary of the Mekong), both
filling during the month of July. Last week alone, the Plei Krong
reservoir rose by 11 meters, filling with an estimated 167 million cubic
meters of water. While the reservoir sizes of these dams are less than a
tenth the size of China’s largest dams, these wet season restrictions
still have a measurable impact on reducing the Mekong floodpulse and its
positive benefits.
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Yali Falls Reservoir, Vietnam
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Where is the water?
We tracked a large cumulative restriction of flow (1.65 billion cubic
meters) at 17 dams across the basin last week. The most significant
restrictions came from Xiaowan (PRC, 921 million cubic meters), Nam Ngum
1 (LAO, 220 million cubic meters), and Plei Krong (VNM, 167 million
cubic meters). Restrictions are common at this time of the wet season
but have a negative effect on the Mekong’s fisheries and agricultural
outputs, which rely on high river levels throughout the wet season.
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Reservoir Storage Over Time
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River Levels
River levels at Chiang Saen are more than two meters below normal and we
estimate 50% of the river’s natural flow is currently being restricted
in upstream dams such as Xiaowan. Above Pakse river levels are below
normal levels. Below Pakse, river levels are slightly above normal. All
gauges throughout the Mekong are trending downward.
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Chiang Saen Gauge
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Stung Treng Gauge
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Weather & Wetness
Above average wetness was observed in much of China’s upper basin, while
it was drier than expected around the Golden Triangle. Eastern portions
of Laos and the highlands of Vietnam were wetter than expected, largely
due to a storm that passed over the area. Northeastern Thailand and
Cambodia had a combination of wet and dry anomalies. Most of the delta
in Vietnam was much wetter than expected, largely caused by
precipitation and an increase in water level on the Mekong River.
Temperatures were slightly above average throughout the basin last week.
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MDM in the News
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