Eight provinces along the Mekong River have been told to brace themselves for a dip in water levels between Jan 1-4 as tests at Jinghong hydroelectric power station in China's Yunnan province are expected decrease of water outflows.
According to the Office of National Water Resources (ONWR), Chiang Rai, Loei, Nakhon Phanom, Nong Khai, Mukdahan, Bung Kan, Amnat Charoen and Ubon Ratchathani will see water levels drop along the Mekong when testing at Jinghong dam begins.
Based on a notification sent by China's Ministry of Water Resources, the tests will see water outflows from the dam reduced from 1,200-1,400 cubic metres per second (m³/s) to between 800-1,000m³/s from Jan 1-3, the ONWR said.
The volume of water discharge will be further reduced to 504-800m³/s on Jan 4, before it returns to its original levels.
Water levels along the Mekong are likely to drop by around 40-60 centimetres in the initial stages of the test. According to ONWR secretary-general, Somkiat Prajamwong, when outflow is restricted to 504-800m³/s, water levels are likely to dip by a further 30-50cm.
"Authorities in affected provinces -- including the Agriculture Ministry -- have been informed about the test at Jinghong Dam so they can better prepare," he said.
According to Mr Somkiat, Chiang Rai will start see water levels drop between Jan 2-5, while Ubon Ratchathani will see the impact between Jan 16-19.
The tests come during a period of severe drought across Thailand.
The Hydro-Informatics Institute said that next year's outlook remains grim as major reservoirs across the country hit critical levels due to lower-than-average precipitation this year.
Nine major reservoirs are currently holding less than 30% of their total storage capacity, namely Lam Phra Phloeng, Lam Nang Rong, Mae Kuang, Pasak, Thap Sela, Krasiew, Khlong Si Yat, Chulabhorn and Ubol Ratana.
According to the institute, the total amount of rainfall in 2019 is 18% below average. Meanwhile, it noted, the amount of rainfall across watershed areas in the central and northern regions is 24% below average.
Even in the South, less-than-average rainfall has been recorded, causing water levels at Ratchaprapa Dam to critically low levels. The wet region faces an increased risk of drought as current dry conditions are expected to continue well into next year.
The institute, which is under the Ministry of Higher Education, Science, Research and Innovation, is also warning of severe saltwater intrusion into the Chao Phraya River during January-March, which will affect tap water production.
Samlae station, which pumps raw water from a section of the Chao Phraya River in Pathum Thani's Muang district, has recorded salt levels of 1.55 grammes per litre at high tide -- higher than the 0.25g per litre threshold.