Update for December 2-15
Notable changes on the Mekong in the last week.
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SPOTLIGHT
2024 Wet Season Dam Restrictions in China: Highest Ever Observed
China’s 12 dams restricted more water than ever before during the wet
season months of June-November 2024. We tracked a total of 23.1 billion
cubic meters of restrictions, slightly higher than 2018’s cumulative
restriction of 22.9 billion cubic meters. For the first time in seven
years, the Nuozhadu Dam (the largest on the Mekong) filled to full
capacity. The dams could fill due to relatively wet conditions in China
throughout the wet season. These restrictions reduced roughly 18% of
natural wet season flow to Chiang Saen, Thailand, which was relatively
low in comparison to previous years given comparatively higher amounts
of precipitation this year. In 2019, 2020, and 2021, China’s dams
restricted 30% of natural flow to Chiang Saen, Thailand, delivering much
more severe negative impacts to the Mekong’s natural floodpulse process
and communities downstream. From here onward into 2025, China’s dams
will release much of these high reservoir volumes into the downstream,
artificially raising the level of the river. In previous years when
China’s reservoirs were similarly high, releases for hydropower
production have TRIPLED monthly flow to Chiang Saen, Thailand and
DOUBLED monthly flow to Stung Treng, Cambodia. Artificially high river
levels are extremely damaging to fish migration behaviors and the
flooded forest areas along the Mekong River on which local communities
rely for food and water security.
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IMAGE OF THE WEEK
2024 Wet Season Flow Wetter in the Upstream and Drier in the Downstream
The Mekong’s downstream reaches usually contribute more wet season flow
than parts of China and northern Laos, but this was not the case in
2024. Combined flow from China, the Golden Triangle, and Northern Laos
accounted for 40% of flow at Stung Treng in 2024 (compared to a
historical average of around 30% prior to 2007 when dams did not impact
natural flow) and flow from northeast Thailand and the 3S Basin
accounted for 30% of flow (their combined historical pre-dam average is
40%). Flow contributions in northeast Thailand were particularly low at
10% due to severe drought there. Over the last 15 years, northeast
Thailand flow contributions have averaged 20% of flow to Stung Treng.
Much of the flow originating in the upstream came from the severe
weather events that hit the upper basin in August and September.
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Where is the water?
Dry season releases for hydropower production have begun and small peaks
of water from dam releases are pushing through the Mekong. Last week we
observed a cumulative release of 601 million cubic meters of water from
13 dams throughout the Mekong, with the most significant release coming
from Nuozhadu (PRC, 496 million cubic meters). These releases
artificially raise the level of the river and cause harm to local
communities and wetlands.
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Most Impactful Dams
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River Levels
River levels throughout the basin are slightly lower than normal.
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Chiang Saen Gauge
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Stung Treng Gauge
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Weather & Wetness
Much higher than normal temperatures in the upper basin in China brought
rain and extreme wetness instead of snow last week. Most of Laos and
Vietnam were also much wetter than normal for this time of year.
Conditions were also wetter than usual in most of Thailand and Cambodia,
although there was a drier than normal area north of the Tonle Sap Lake
near Siem Reap that has persisted for many weeks.
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