Floods are the most widespread and frequent natural
disasters caused by extreme rainfall and are responsible
for significant loss of lives and property (Smith and
Ward 1998; Ashley and Ashley 2008; Gruntfest 2009;
Adhikari et al. 2010). Floods occur when prolonged rain
falls over several days, or intense rain falls over a short
period, that exceeds the capacity of the underlying
ground or drainage systems, leading to flash floods,
overflow of streams, and breach of levees. Heavy
rain also has the potential to trigger landslides in mountainous areas with the right combination of topographic
slope, soil type, and vegetation. Severe mudslides
can be very devastating when they occur in a
populated area. For example, a massive rock slide–
debris avalanche occurred on 17 February 2006 in the
Philippine province of Southern Leyte following a 10-day
period of heavy rains. The deadly landslide caused
widespread damage with a death toll estimated to be
1126. In August 2009, extreme rain from Typhoon
Morakot triggered enormous mudslides and severe
flooding throughout southern Taiwan. One mudslide
buried the entire town of Xiaolin, killing an estimated
500 people in the village alone.