Southeast Asia & the Pacific: Widespread water surpluses will persist

25 August 2022

THE BIG PICTURE
The 12-month forecast through April 2023 indicates widespread surpluses of varying intensity in many regions of Southeast Asia. Surpluses are also expected in the Philippines and central and eastern Indonesia.

In Myanmar, surpluses of varying intensity are forecast throughout much of the nation with a few pockets of transitional conditions (pink/purple). Though most of western Thailand will see near-normal conditions, surpluses will dominate much of the nation’s eastern half and will include severe to exceptional surpluses in the Chi River Basin. Cambodia, too, can expect widespread surpluses east of Tonlé Sap with exceptional anomalies following the Mekong River. Surpluses are forecast in Laos and Vietnam, severe to extreme in northern Laos.

In the Philippines, surpluses will be severe in the central islands, moderate to severe in northern Mindanao, and moderate in isolated pockets of Luzon.

Moderate deficits are forecast in a few pockets of Sumatra including near the city of Medan in the north and in the central provinces of Riau and West Sumatra. Surpluses will be widespread in Indonesian Borneo, moderate overall but more intense in the west (south of the Kapuas River) and in the Mahakam River region in the east. Surpluses are forecast in Sulawesi, southern Java, the Lesser Sunda Islands, the Maluku Islands, and in the Bird’s Head Peninsula (Doberai Peninsula), nearby Fakfak Peninsula, and southern extreme of Papua, Indonesia. Anomalies will be especially intense in the Fakfak Peninsula, nearby small islands, and Flores Island.

Deficits are forecast on Papua New Guinea’s central north coast, and in New Britain and the Solomon Islands.

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

The forecast through October indicates widespread surpluses in Southeast Asia from eastern Thailand through Cambodia, Laos, and most of Vietnam. Surpluses will be intense in Thailand’s Chi River Basin and in the Mekong River region through Cambodia and the Delta. Mixed conditions are forecast in Myanmar: transitions and deficits in the center of the nation surrounded by pockets of surplus. In the Philippines, surpluses will be severe in the central islands and extreme in eastern Mindanao. Deficits are forecast in central Sumatra, surpluses in the southeast and Singapore. Surpluses will be widespread in Borneo, Java, Sulawesi, Flores Island, the Maluku Islands, most of Indonesian Papua and well into central Papua New Guinea. Deficits are forecast for much of New Guinea’s north coast, the Bird’s Tail Peninsula (Papuan Peninsula), and pockets on the Gulf of Papua, as well as in New Britain and the Solomon Islands.

From November2022 through January 2023, surpluses will shrink and downgrade considerably. Moderate surpluses are forecast in eastern Thailand, Laos, eastern Cambodia, and Vietnam’s Central Highlands. Surpluses will nearly disappear from Myanmar and moderate deficits are forecast north of Mandalay. A few pockets of moderate surplus will linger in the Philippines. Moderate deficits will emerge in the Malay Peninsula and deficits will increase in Sumatra including severe anomalies in central Sumatra. Surpluses are forecast in the Lesser Sunda Islands, the Maluku Islands, Sulawesi’s peninsulas, and coastal pockets of Indonesian Borneo. In New Guinea, surpluses will persist in the Bird’s Head and Fakfak Peninsulas, southern Papua, and pockets in the Highlands. Deficits will retreat from the Papuan Peninsula and around the Gulf of Papua as some surpluses emerge. Moderate surpluses will emerge in western New Britain while deficits persist in the east and in the Solomons, though anomalies will shrink and downgrade.

The forecast for the final months – February through April 2023 – indicates moderate surpluses in eastern Thailand, Laos, eastern Cambodia, and the Central Highlands of Vietnam. Some deficits are forecast in Sumatra.

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

IMPACTS
Heavy precipitation continued to trigger flooding in many parts of Southeast Asia from July into August.

With intense rainfall reaching 80 mm (3 inches) per hour, some streets in Bangkok quickly became submerged under nearly a foot of water in mid-August. Blackouts were reported due to storm damage. Bangkok revived a pre-covid pandemic inmate sewer cleaning program - involving prisoners who volunteer to clear debris from the sewers in exchange for reduced sentencing - to help prevent excessive flood damage.

In northeast Thailand’s Chi and Mun River Basins, floodwaters covered 20,800 hectares of land, over half of which was rice fields. In the nation’s northwest near the border with Myanmar, the Sai River overflowed, flooding a border checkpoint and market area and leaving some residential areas sitting in a meter of water.

Sixteen provinces in Cambodia reported flooding in early August, inundating about 40,000 hectares of rice. In the middle of the month, the Stung Sen River in Kampong Thom Province near Tonlé Sap overflowed, flooding rice fields and lowland homes.

In Laos, military personnel were deployed to assist in flood relief efforts in the north. Several rivers overflowed, flooding villages, roads, and tourist areas, and destroying bridges and disrupting power.

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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