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 16.60 millimetres (mm) to 182.00 mm.
There will be average rainfalls for the next 5 days over the Mekong region from 21 to 25 September 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 a significant decrease over the monitoring period from 10 to 20 September 2021. It dropped about 0.89 m from 535.98 m on 10 Sept to 535.09 on 13 Sept 2021 (recorded on 7:00 am). The outflows decreased from 1,318 m3/s on Sept 10 to 727 m³/s on Sept 20, 2021. Water level was 0.14 m lower than its minimum level during 19-20 September 2021.
Along with the significant low outflow from Jinghong upstream, water levels of monitoring stations at Chiang Saen in Thailand also decreased about 0.48 m from 7 to 20 September 2021. From Chiang Khan in Thailand to Vientiane in Lao PDR, water levels decreased during 14-20 September due to below-average rainfall in the area.
However, water levels from Nakhon Phanom in Thailand to Savannakhet in Lao PDR slightly increased. Water levels from the stretches of the river from Stung Treng to Kratie and at Kampong Cham in Cambodia also dropped, following the same trend of the upstream flow (at Pakse) and staying lower than their LTA.
The water volume of the Tonle Sap Lake is lower than its LTA but higher than the levels in 2019 and 2020 during the same period.
Over the next few days, the water levels across most monitoring stations are expected to slightly increase but remain lower than their long-term average value in most stations.
Drought condition and its forecast
Some areas of the upper part of the LMB were moderately dry during the reporting week due to moderately dry meteorological and agricultural indicators. Those areas cover Chiang Rai and Phayao of Thailand and Phongsal and Xiengkhuang of Lao PDR. The rest of the region was normal. No significant threat was found from 11 to 17 September 2021.
For the upcoming thee-month forecast, the LMB is likely to receive above average rainfall in September and 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.