December 22, 2022 - The Weakening Pulse of Tonle Sap

Tonle Sap
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Cambodia’s Tonle Sap is a lake with a “pulse”, and in recent years that
life-giving pulse has grown weaker.

During the dry season, the Tonle Sap River drains water from Tonle Sap
Lake and carries it to help fill the large Mekong River. In June, as
monsoonal rains fill the Mekong, floodwaters pour into Tonle Sap River.
And then the that river reverses course and pours into Tonle Sap Lake,
filling the lake with fresh water. This influx can easily triple the
size of the lake and raise the depth from roughly 2 meters (6.5 feet)
to 10 meters (32 feet), making Tonle Sap Asia’s largest lake and
freshwater fishery.

The importance of the seasonal pulse of Tonle Sap can’t be overstated.
The flooding creates a massive lake and large, seasonal, freshwater
wetlands that supports a superb fishery. The silt, nutrients, and
moisture deposited during the monsoonal floods also renew farmland and
forest. However, a series of dams along the Mekong—at least 11 were
functioning in 2020 with up to 24 total planned—have severely slowed
the seasonal inundation of Tonle Sap, with negative consequences on
fishing, agriculture, the ecosystem, and the livelihoods of those who
depend on the lake.

On December 12, 2022, the Moderate Resolution Imaging Spectroradiometer
(MODIS) on board NASA’s Terra satellite acquired a true-color image of
a nearly-full Tonle Sap (top image). The lower image is of the same
area and was acquired on January 16, 2001, also by Terra’s MODIS. One
of the most striking changes is the near-disappearance of the
fresh-water streams and associated floodplains and deltas around Tonle
Sap, especially on the northern shores of the lake. In 2001, these are
seen as streaks of tan cutting through green vegetation and widening to
v-shapes at the shoreline. In 2022, they are nearly absent.

Image Facts
Satellite: Terra
Date Acquired: 12/12/2022
Resolutions: 1km (96.2 KB), 500m (239.3 KB), 250m (171.6
KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2022-12-22

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