| Summary: | ABSTRACT: The December 2011 disaster in the Philippines which was induced by TS Washi was investigated. This disastrous event which claimed 1,268 human lives and PhP1.455 Billion (US$63.26M) damages to infrastructure and agriculture was analyzed in terms of meteorological, hydrological, environmental and social aspects. Government’s response to the disaster was also included. Meteorological analysis was carried out using surface observations, satellite data and simulation of numerical weather prediction model. Intense short duration rainfall upstream the river basin and the damming effect along the river triggered the flashfloods downstream in Cagayan de Oro and Iligan Cities. The strong storm winds coupled with orographic lifting enhanced the rainfall activity over the mountain. The encroachment in the sandbars and the river banks due to urbanization and unabated development impeded the flow of water resulting to greater damage. In addition, the timing of the high tide constrained the flow of the flood waters that resulted to widespread flooding in the downstream areas. This flood event on 16 December 2011 reached a maximum height of 7 meters and the extent of inundation covered about 7 to 10 meters high from the river banks in Cagayan de Oro City.The conclusion was that the disaster was the result of the interplay of climatic, environmental and social factors. As a result of the flood disaster and based on the findings of the different agencies, the Philippine government came up with various recommendations which include regulation of the development in the floodplain areas, hazard mapping and installation of early warning system. Keywords: tropical storm Washi, forecast rainfall, satellite based information, flashflood disaster, river basin management
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