Southeast Asia & the Pacific: Widespread water surplus will persist

20 October 2022

THE BIG PICTURE
The 12-month forecast through June 2023 indicates widespread water surpluses in much of Southeast Asia, exceptional in many regions. Surpluses are also expected in the Philippines and central and eastern Indonesia.

In Southeast Asia, surpluses are forecast from Myanmar through Vietnam with widespread exceptional anomalies from eastern Thailand through central Cambodia. Surpluses will also be exceptional from the Sittang River in eastern Myanmar past the Salween River to the Ping River in western Thailand, and south along the Chao Phraya River to Bangkok. The Mekong Delta can expect extreme to exceptional surpluses, and extreme surpluses are forecast in Vietnam’s Central Highlands.

In the Philippines, surpluses will be intense in the Visayas, and moderate to severe in northeastern Luzon and northern Mindanao.

Some pockets of deficit are predicted in Peninsular Malaysia and central Malaysian Borneo, as well as a pocket in northern Sumatra near Medan City, while surpluses are forecast in southwestern Sumatra. Surpluses will be widespread and intense in West Kalimantan in Indonesian Borneo, and moderate in several river basins elsewhere in Borneo. Surpluses of varying intensity are forecast along Java’s southern coast, and in Sulawesi, the Lesser Sunda and Maluku Islands, and the Bird’s Head Peninsula, Fakfak Peninsula, and southern Papua, Indonesia. In Papua New Guinea, surpluses are expected in the Southern Highlands and southern coastal areas. Pockets of deficit are forecast on New Guinea’s north coast and nearby small islands.

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

The forecast through December indicates that widespread surpluses will continue in many areas including Southeast Asia where exceptional anomalies are forecast from eastern Thailand through central Cambodia, and from the Sittang River past the Salween River in Myanmar. Normal conditions will return to the Malay Peninsula, central Malaysian Borneo, and northern and central Sumatra. Surpluses in the Philippines are expected to moderate. Widespread surpluses are forecast in Indonesian Borneo, Sulawesi, Java, the Lesser Sunda and Maluku Islands, and most of New Guinea. Anomalies will be intense in many regions including the Lesser Sundas and Sulawesi. Deficits are expected along the north coast of Papua New Guinea and in nearby islands.

From January through March 2023, surpluses will shrink and downgrade considerably. However, widespread surpluses will persist in Southeast Asia in southeastern Myanmar, Thailand, central and eastern Cambodia, northeastern and southern Laos, and most of Vietnam. Surpluses will be exceptional in Myanmar and from eastern Thailand through central Cambodia. Moderate surpluses are forecast in the Philippines, primarily in the Visayas. Pockets of deficit will emerge in the Malay Peninsula, Borneo, Sumatra, and western Java as surpluses retreat. Deficits will also emerge in a pocket of central Sulawesi while surpluses, primarily moderate, persist in Sulawesi’s northern arm, the Lesser Sunda Islands, and pockets in the Malukus. Surpluses will linger in the Bird’s Head Peninsula, southern coastal areas of New Guinea, and the Southern Highlands, while retreating from the north coast.

The forecast for the final months – April through June 2023 – indicates that surpluses will continue to shrink and downgrade, and deficits will increase. Areas with a forecast of surplus in Southeast Asia include Rakhine State in Myanmar, the Sittang River region, central Thailand, and the Highlands and North Central Coast regions of Vietnam. Deficits, generally moderate, are forecast for Malaysia, and pockets of Sumatra, Java, Sulawesi, and New Guinea. Small pockets of surplus will persist in the Philippines, northern Sulawesi, the Lesser Sundas, and along New Guinea’s south coast.

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

IMPACTS
Flooding continued to affect many regions of Southeast Asia, the Philippines, and Indonesia in September and October.

Typhoon Noru claimed 16 lives in Cambodia, submerging thousands of homes and damaging many roads. Heavy rainfall continued for weeks, affecting over 85,000 households in 14 provinces, along with health centers, schools, and agricultural land.

Noru caused flooding in several northern provinces of the Philippines as well, dumping 283 millimeters (11 inches) of rainfall in just 24 hours. Five rescue workers were killed during flash flooding. The Typhoon, known as Karding in the Philippines, caused an estimated P3.12 billion (US $53.4 million) in agricultural damages.

Late September rainfall triggered a landslide near a gold mine in South Kalimantan Province, Indonesia that left six people dead.

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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