Multi-hazard Risk Assessment Using GIS in Urban Areas: A Case Study for the City of Turrialba, Costa Rica

In the framework of the UNESCO sponsored project on “Capacity Building for Natural Disaster
Reduction” a case study was carried out on multi-hazard risk assessment of the city of Turrialba, located
in the central part of Costa Rica. The city with a population of 33,000 people is located in an area, which
is regularly affected by flooding, landslides and earthquakes. In order to assist the local emergency
commission and the municipality, a pilot study was carried out in the development of a GIS –based
system for risk assessment and management.
The work was made using an orthophoto as basis, on which all buildings, land parcels and roads, within
the city and its direct surroundings were digitized, resulting in a digital parcel map, for which a number
of hazard and vulnerability attributes were collected in the field. Based on historical information a GIS
database was generated, which was used to generate flood depth maps for different return periods. For
determining the seismic hazard a modified version of the Radius approach was used and the landslide
hazard was determined based on the historical landslide inventory and a number of factor maps, using a
statistical approach.
The cadastral database of the city was used, in combination with the various hazard maps for different
return periods to generate vulnerability maps for the city. In order to determine cost of the elements at
risk, differentiation was made between the costs of the constructions and the costs of the contents of the
buildings. The cost maps were combined with the vulnerability maps and the hazard maps per hazard
type for the different return periods, in order to obtain graphs of probability versus potential damage.
The resulting database can be a tool for local authorities to determine the effect of certain mitigation
measures, for which a cost-benefit analysis can be carried out. The database also serves as an important
tool in the disaster preparedness phase of disaster management at the municipal level.