Debris flow warning system in Taiwan uses effective accumulated precipitation as the warning criteria. Little research has studied the affected area associated with different levels of accumulated precipitation. The Taipei DF024 potential debris flow torrent is used as an example to
study the relation between an affected area and accumulated precipitation. Three different amount of accumulated precipitation 300, 500 (official warning criteria) and 700 mm in 24 hours are chosen for comparison. Average rainfall intensity per hour is calculated from accumulated rainfall through the Monobe formula. Total water flow rate is estimated using the Rational formula and a discharge hydrograph.Maximum debris flow volume is determined by the equilibrium concentration formula. All sources of debris are distributed on landslide areas and river bed from field investigation. DEBRIS-2D is used to simulate debris flows. The results show that the hazard area is proportional to
precipitation, and the thickness of maximum debris flow accumulation is between 3 and 3.5 m for all three cases. The relation between accumulated precipitation and hazard area can provide officials with additional information related to resident evacuation.
Key Words : Accumulated precipitation、DEBRIS-2D、hazard area.