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Weekly Wet Season Situation Report in the Lower Mekong River Basin - 13-19 July 2021

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Situation Report
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Key messages

Key messages for this weekly report are presented below.

Rainfall and its forecast

  • Rainfall took place from Chiang Sean in Thailand to Pakse in Lao PDR, including the lower part in Cambodia and Viet Nam, varying from 11.70 millimetres (mm) to 247.70 mm.

  • There will be a significant rainfall is projected for the next 5 days in the Mekong region from 20 to 26 July 2021 because of low-pressure nominated in the Mekong region.

Water level and its forecast

  • The outflows at Jinghong hydrological station increased over the monitoring period from 13 to 19 July 2021. It rose about 0.45 m from 535.60 metres (m) on July 12 to 536.05 m on July 19. The outflows increased from 1,050 cubic metres per second (m³/s) on July 12 to 1,368 m³/s on July 19.
    Due to below average rainfall from June 30 to July 19 and decreased flow from Jinghong upstream at the same period, water levels across most monitoring stations from Chiang Saen in Thailand to Thakhek in Lao PDR were decreasing, and from the stretches of the river between Stung Treng, Kratie and Kompong Cham in Cambodia were also repeatedly decreasing and staying lower than their LTA.

  • The water volume of the Tonle Sap Lake during this reporting period was slightly higher than that in 2020 of the same periods but was still lower than its long-term average.

  • Over the next few days, the water levels across most monitoring stations are expected to rise but are forecasted to stay lower than their long-term value.

Drought condition and its forecast

  • The LMB did not face any significant threat during July 3-9. The region was mostly at normal conditions except some moderate drought taking place in the central part of the LMB covering some areas of Sakon Nakhon, Roi Et, Yasothon, Surin, Si Saket, Ubon Ratchathani, and Sekong.

  • The ensemble prediction model forecasts that in July the LMB is likely to receive from below-average to average rainfall for the entire region; Cambodia, the Central Highlands of Viet Nam, and southern Lao PDR will be the driest areas. In August and September, eastern Cambodia and the Central Highland of Viet Nam are forecasted to experience some meteorological drought, a situation when there is a prolonged period with less than average rainfall. Fortunately, the models show that the LMB might receive much above average of rain during October.