A flood warning in Sarawak is not one decision by one body. It is two systems meeting. MetMalaysia forecasts the rain and issues warnings in named categories; the Department of Irrigation and Drainage (DID) Sarawak measures what the rivers do about it, at 115 stations that each carry their own alert, warning and danger mark in metres. Neither body orders anyone out of a house. That is the State Disaster Management Committee, working through divisional committees and the state operations room in Kuching.

What actually triggers a rain warning

MetMalaysia publishes a hard number for exactly one warning type. Its thunderstorm warning criteria set the trigger at rain intensity exceeding 20 mm per hour, observed or expected from station readings, radar and satellite images. A single thunderstorm warning runs no longer than six hours; if the weather is expected to outlast that, it is upgraded into the continuous rain category.

The continuous rain criteria are graded but not numerical:

  • Alert — continuous rain is expected within one to three days, or rain already falling is expected to continue.
  • Severe — continuous heavy rain is expected.
  • Danger — continuous torrential rain is expected.

No millimetre threshold separates heavy from torrential on that page, so that step rests on the forecaster's judgement. Note too that "alert" does duty in both systems: a rain forecast in MetMalaysia's, a measured river height in DID's.

What the river gauges measure, and what the bands mean

DID Sarawak runs iHYDRO, a state-wide network of gauges reporting river heights and rainfall through the day. On 28 August 2026 its water level table listed 115 stations across twelve divisions and 26 river basins, each with its own normal, alert, warning and danger figures.

Each station is filed as below normal, normal, alert, warning or danger. The station map attaches instructions to the top two: past the alert mark, nearby communities are told to be alert at all times; past the warning mark, to be cautious.

At 04:45 on 28 August 2026, one of the 115 sat above those marks: Pusa, on the Batang Saribas in Betong, reading 3.27 m against marks of 2.62 m (alert), 3.22 m (warning) and 3.82 m (danger).

Why a high reading can be normal and a low one serious

The thresholds are set per station, not state-wide. On the same table, Aman 5 Bridge on Sungai Sarawak carries a danger level of 38.00 m, while Sibu Laut reaches danger at 2.80 m. The gauges also use two reference datums, assumed level and mean sea level, marked station by station. A reading means nothing until it is set against its own station's figures.

The gap between normal and alert matters too. Batu Kitang Telemetry, one of the Sungai Sarawak gauges in our Kuching division area, sits at a normal level of 1.85 m but does not reach alert until 3.00 m, warning until 4.50 m and danger until 5.00 m. Kuching holds 24 of those stations, Sibu 22 and Limbang three.

Who decides to move people

Response sits with the State Disaster Management Committee (SDMC). Setting out its northeast monsoon posture in December 2024, Deputy Premier and SDMC chairman Datuk Amar Douglas Uggah Embas put 7,507 personnel on standby — 2,759 from the Civil Defence Force, 1,880 from Social Welfare, 1,462 from Fire and Rescue and 1,406 police — with 760 assets behind them, including 214 boats, 260 four-wheel drive vehicles, four helicopters and 15 drones, held at 31 forward bases and a main depot at Kota Samarahan.

Each division also runs a Divisional Disaster Management Committee, which coordinates on the ground — as in Bintulu in February 2025, when the state secretary visited an evacuation centre at the civic centre there. Day-to-day figures come from JPBN at the state operations room in Wisma Bapa Malaysia, Petra Jaya, which reports evacuation centres, affected areas and schools hit by flooding, on 082-443991 and 082-447960.

The monsoon is not the whole story

MetMalaysia dates the northeast monsoon from November to March and the southwest monsoon from late May to September, and identifies the northeast as the wetter of the two for western Sarawak — the season the SDMC staffs up for.

DID's own register complicates that. Its record for August to October 2025, outside the northeast monsoon, logs floods across at least seven divisions, and shows two mechanisms. One is rainfall exceeding what drains can carry, as at Lorong Bunga Melor in Serian on 8 August 2025, at 0.30 m. The other is river overflow arriving with a high tide, logged through September in Limbang, Sarikei and along the Batang Rajang in our Sibu division area. The deepest entries are from Saratok on 17 October 2025, at 1.40 m to 1.50 m.

What the official advice says

DID publishes flood preparedness guidelines attributed to the Civil Defence Department. Before: learn the local warning arrangements, clear the drains, know where the evacuation centre is. During: listen for announcements, leave when told to, never try to cross a flooded road, stay away from electrical hazards. After: wait for the area to be cleared, check the building, and throw away food that has touched floodwater.

Between warnings, the measurements are open to anyone: iHYDRO's station tables carry every reading and every threshold behind them.

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