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Weekly Wet Season Situation Report in the Lower Mekong River Basin - 05-11 October 2021

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Mekong River Commission
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Key Messages

Key messages for this weekly report are presented below.

Rainfall and its forecast

  • Rainfall focused in the areas from Chiang Saen in Thailand to Pakse in Lao PDR, including the lower part in Cambodia and Viet Nam, varying from 3.20 millimetres (mm) to 135.60 mm.

  • There will be average rainfalls for the next 5 days over the Mekong region from 12 to 18 October 2021 due to low-pressure dominating the Mekong region.

Water level and its forecast

  • According to MRC’s observed water level data, the outflows at Jinghong hydrological station showed water level changes over the monitoring period from 5 to 11 October 2021. Water levels at this station significantly increased from 535.27 m on 8 Oct to 536.03 on 11 Oct 2021 (recorded on 7:00 am) and stayed about 0.21 m higher than its long-term-average (LTA) value. The outflow was up from 832 m3/s on 8 Oct to 1354 m³/s on 11 Oct 2021. From October 8 to 11, water level at this station rose about 0.77 m and was about 0.11 m higher than its LTA value.

  • Amid the significant increased outflow from Jinghong upstream, water levels of monitoring stations at Chiang Saen in Thailand still decreased from 5 to 11 October 2021. Moreover, from Chiang Khan in Thailand to Vientiane in Lao PDR, water levels decreased about 0.30 m during October 5-11 due to less rainfall in the area and influence of dam operation. Water levels from Nakhon Phanom in Thailand to Savannakhet in Lao PDR were also decreasing. Unlike, the above stations, water levels from the stretches of the river from Stung Treng to Kratie and at Kampong Cham in Cambodia were significantly increasing, due to high rainfall and following the same trend of the upstream flow (at Pakse and 3S area in Viet Nam).

  • The water volume of the Tonle Sap Lake was lower than its LTA and the levels in 2019 but was higher than 2020 during the same period from 5 to 11 October 2021.

  • Over the next few days, the water levels across most monitoring stations are expected to increase but remain lower than their long-term average value in most stations.

Drought condition and its forecast

  • Soil moisture conditions were anomaly dry in some areas of the upper part of the LMB. However, the combined drought indicator shows that the LMB did not face any significant drought during the monitoring week from October 2 to 8. The entire LMB region received from average to above average rainfall.

  • For the upcoming thee-month forecast, the LMB is likely to receive above average rainfall in October mainly in the central and southern parts of the region. Like 2020, the forecast shows that October is likely the wettest month of the year. November is forecasted to receive from average to above average rainfall throughout the LMB; the wetter part is likely to take place in the south. Lastly, in December the forecast shows some rain which likely take place in the south of the region.