The Krueng Tamiang lowland, between the Simpang Kiri and Simpang Kanan gauges and the Malacca Strait, flooded for more than a week after Cyclone Senyar crossed northern Sumatra in late November 2025. This viewer shows the lab’s hourly hindcast of that flood: water depth on a 90-m grid, the time and depth of the peak at every cell, how long each place stayed under water, the design-flood maps for comparison, and the flood extent that UNOSAT mapped from Sentinel-1 radar on 28 November.
Project details
- Area covered
- 835 km² of lowland
- Peak flooded area
- 605 km² deeper than 0.3 m
- Model
- VFlood 1.1, 2D local-inertial shallow water, coupled river–floodplain friction, GPU
- Grid
- 3 arc-seconds (about 90 m), 390 × 378 cells
- Terrain
- FABDEM bare-earth DEM with a WorldCover sea mask
- Inflows
- Hourly hydrographs of Kr. Simpang Kiri and Kr. Simpang Kanan from mHM 5.13, calibrated to the Tanjung Mancang stage record
- Rain on the floodplain
- GPM IMERG Late, hourly
- Period
- 18 November – 5 December 2025 (408 hourly outputs)
- Check against satellite
- On open land (cropland, grass, built-up) against the UNOSAT Sentinel-1 extent of 28 November: POD 0.99, FAR 0.52, CSI 0.48
Read with care
- Results are a simulation of what the terrain, inflows and rain imply, not an observation of what happened.
- Discharge magnitude follows the IMERG rain volume, because the only gauge records stage and its rating could not be pinned down.
- Most of the area the model floods beyond the satellite extent lies under oil palm and mangrove, where Sentinel-1 radar rarely sees standing water.
- Do not use these maps for emergency response, design or legal decisions.
Simulation: Hydroinformatics Laboratory, Universitas Gadjah Mada. Terrain: FABDEM (Univ. of Bristol, CC BY-NC-SA 4.0). Rivers: © OpenStreetMap contributors (ODbL). Observed extent: UNITAR/UNOSAT. Rain: NASA GPM IMERG. Basemaps: Esri, CARTO.