Southeast Asia & the Pacific: Water deficits will persist in Thailand

18 August 2020

THE BIG PICTURE
The 12-month forecast through April 2021 indicates moderate to exceptional deficits in western Thailand reaching across the border into southern Myanmar. Moderate deficits are forecast for eastern Thailand spanning the Mekong River into central Laos, and in northeastern Vietnam.

Surpluses of varying intensity are forecast for many regions in Myanmar and will be particularly intense west of the Irrawaddy River.

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Severe surpluses are expected in eastern Cambodia and well into Vietnam as far south as Ho Chi Minh City. Primarily moderate surpluses are forecast for northeastern Laos and pockets in the peninsular regions of Thailand and Myanmar.

Surpluses are also forecast in a few pockets in Malaysia and many pockets in Indonesia. Anomalies will be intense in Aceh Province in northern Sumatra and in northern Sulawesi. Other areas with a forecast of surplus include pockets of Borneo, eastern Java, Flores Island, eastern Sulawesi, many small Indonesian islands, and the Bird’s Head Peninsula (Doberai Peninsula) and other areas in Papua, Indonesia. In Papua New Guinea, intense deficits are expected along the western shore of the Gulf of Papua and moderate surpluses in the central Highlands. Nearly normal conditions are forecast for the Philippines with a few pockets of moderate surplus

FORECAST BREAKDOWN
The 3-month maps (below) show the evolving conditions in more detail.

The forecast through October indicates that surpluses will shrink and downgrade overall but persist in many areas, particularly Indonesia. In Southeast Asia, surpluses are forecast for western and northern Myanmar; pockets in the Malay Peninsula; northeastern Laos; and from eastern Cambodia into southeastern Vietnam. Deficits will shrink considerably in Southeast Asia, persisting primarily in western Thailand and reaching into Myanmar’s Kayin State. Normal conditions are expected in western Cambodia as deficits retreat.

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Surpluses are forecast in many parts of Malaysia and Indonesia. Anomalies will be exceptional on Flores Island and intense at each end of Sumatra and Java and in northern Sulawesi. Intense deficits will emerge on Timor Island. Deficits will shrink and downgrade on New Guinea, nearly disappearing in the west (Papua, Indonesia) but will remain intense along the western shore of the Gulf of Papua in Papua New Guinea and moderate along the central north shore of the nation. Surpluses are forecast for many other regions on the island but will be most widespread in the west, particularly in the Bird’s Head Peninsula. In the Philippines, moderate to extreme surpluses are forecast for eastern Mindanao, mild surpluses in the central islands, and nearly normal conditions in Luzon.

From November 2020 through January 2021, water conditions in many parts of the region will normalize. Moderate deficits are expected in western Thailand and northeastern Vietnam and moderate surpluses from eastern Cambodia into southeastern Vietnam, and a few isolated pockets in Laos. In Myanmar, surpluses of varying intensity will persist in pockets of the north, moderate surpluses in the southwest border area, and both deficits and surpluses (pink/purple) in the southwest and along the Irrawaddy in the Delta. Surpluses, primarily moderate, are forecast for northeastern Sulawesi, Flores Island, and other small islands in Indonesia; the Bird’s Head Peninsula on New Guinea and some other pockets of the island; and the central islands of the Philippines. A few small, isolated pockets of exceptional deficit are forecast in northwestern Borneo and Sarawak in Malaysian Borneo.

The forecast for the final months – February through April 2021 – indicates mild to moderate deficits in western Thailand and a few other pockets in Southeast Asia and in Peninsular Malaysia, Sumatra, and Java. Small pockets of surpluses will persist in Myanmar and Southeast Asia.

Please note that WSIM forecast skill declines with longer lead times.

IMPACTS
Though annual flow reversal has begun on the Tonlé Sap River, the water level in Tonlé Sap Lake, source of more than half of Cambodia’s fish, remained critical in mid-August, according to the Mekong River Commission. Low levels on the Mekong delayed the reversal that feeds the lake until early August. The country’s annual water festival marking the end of Tonlé’s wet season in late October has been cancelled, a decision prompted by drought and the COVID-19 pandemic.

Water levels nation-wide in Cambodia’s dams were at 41 percent of total capacity in early August with only 17 percent usable, according to water authorities. Less water than expected has flowed into the country’s 38 major dams, prompting fears of a drought.

Flooding and landslides killed 5 people in northern Vietnam’s Ha Giang Province after 401 millimetres (15.8 inches) of rain fell during a 24-hour period in late July.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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