Flash flood impacts of Hurricane Otto and hydrometeorological risk mapping in Costa Rica

ABSTRACT Flash floods are one of the most damaging natural hazards in tropics. Seasonal and extraordinary rainfall recurrently trigger flash floods in Costa Rica. Hurricane Otto was the first reported hurricane to have ever passed through Costa Rica. The phenomenon resulted in losses amounting to 190 million US$, leaving four casualties and ca. 69 million US$ of losses in Upala municipality in northern Costa Rica, alone. On November 24, 2016, the passage of Hurricane Otto produced ~300 mm of rain over the study region in 6 h. We carried out a hydrometeorological risk assessment based on population census minimum geostatistical units to present a spatially distributed risk matrix assessment. In addition, we applied an S1 GRD (Ground Range Detected) and VV polarization to Sentinel-1 SAR (synthetic aperture radar) and WorldView-3 and WorldView-4 images to determine the flash-flooded areas just after Hurricane Otto’s impact in the Zapote River, Cabeza de León and Guacalillo sub-basins mainly in Upala municipality. Consequently, we compared the flash-flooded areas with the different previous hydrometeorological risk zones. Flash floods affected ~74 km2 and 56% of these areas coincided with high-risk zones. The results and methodology of this study can be useful to assess extraordinary hydrometeorological hazards in developing and tropical countries.