Caribbean Disaster Mitigation Project
Implemented by the Organization of American States
Unit of Sustainable Development and Environment
for the USAID Office of Foreign Disaster Assistance and the Caribbean Regional Program


CDMP Storm Hazard Modeling

An accurate understanding of how a hazard can affect an area is critical to design appropriate responses to that hazard. To better understand the effects of tropical storms in the Caribbean, the CDMP has supported the development of a storm hazard model, which can assess the risk to coastal areas in the Caribbean from surges, waves and high winds produced by such storms. Critical to the applicability of this model to the Caribbean region is that it can be quickly adapted to new locations while producing high quality predictions. CDMP has installed this model, TAOS/L, at the Caribbean Institute for Meteorology and Hydrology (CIMH) and has provided its staff with the training and support necessary to apply the model within its member countries. With TAOS/L, CIMH has the capacity to produce storm surge, wind and wave action studies throughout the Caribbean. Such information can be used for emergency evacuation and coastal land use planning, as well as the design of standards for infrastructure. TAOS/L is not a storm forecasting tool. In conjunction with storm forecasts from national meteorological services or the US National Hurricane Center, however, TAOS/L can be used to understand the effects of a storm's predicted track and intensity. See the document Tropical Cyclone Forecasting for more information on this topic. CIMH has developed a plan to use TAOS/L as a tool during storm events to help identify areas of impact, given a predicted storm track.

TAOS/L is a computer-based numerical model that produces estimates of maximum sustained wind vectors at the surface, and still water surge height and wave height at the coastline, for any coastal area in the Caribbean basin. TAOS/L is a Caribbean version of the TAOS model and was developed for the CDMP by Charles Watson. The model relies on a generic data base structure, and uses USGS digital data for deep ocean bathymetry, Digital Chart of the World data for land boundaries and rough topography, satellite imagery for foreshore bathymetry and land cover, and the National Hurricane Center data base for storm data. Model runs can be made for any historical storm, for probable maximum events, or using real-time tropical storm forecasts from the US National Hurricane Center (NHC). TAOS/L is integrated into a geographic information system (GIS), which eases entry of model data, enables the presentation of model results in a format familiar to meteorological officials in the Caribbean region and allows the results to be combined with locally available GIS and map information.

Within the CDMP, TAOS has been used to map storm-related hazards in numerous hazard assessments. A 1995 study of Parham harbour, Antigua, included modeling of storm surge and inland flood hazards. In 1996, TAOS was used to assess coastal surge and inland wind hazards in Belize, and, as part of a CDB-funded coastal rehabilitation project, to assess storm surge and wave effects on the west coast of Dominica. In 1998, CIMH produced Maximum Envelope of Water (MEOW) maps for storms of varying magnitude, heading and forward speed for the islands of Antigua and Barbuda. In December 1998, CDMP sponsored a national workshop in Antigua to discuss these maps and to develop guidelines for the use of the maps in development and emergency planning. Results from this pilot project were used in the development of storm hazard atlases for eastern Caribbean states in 1999. See the progress bulletin "National-level Storm Hazard Mapping" for more information on these activities.

In 1997, a new approach to storm hazard modeling using TAOS was developed. For the Montego Bay Coastal Hazard Assessment, TAOS results were used within a statistical framework to estimate surge heights for various return periods. The return-period approach developed for Montego Bay was subsequently used to develop return-period based maps for the State of Florida and, as part of the Kingston Multi-hazard Assessment, similar information was produced for Kingston Jamaica. In conjunction with the Kingston assessment, regional storm hazard information for the entire Caribbean basin was developed. This data set contains estimates of maximum surge, wave height and wind speed for 10-, 25-, 50- and 100-year return periods. These estimates are available for each cell in the Caribbean grid at 30-arcsecond (approximately 1 km) intervals. The products of this work will be available in the early 2000.

A technical description of the TAOS model is available in the document Design, Implementation and Operation of a Modular Integrated Tropical Cyclone Hazard Model. The statistical approach to return period estimation is discussed in detail in the document Hurricane Return Period Estimation. A more detailed description of CDMP applications of the TAOS/L model is available in the document The TAOS/L Storm Hazard Model and CDMP TAOS/L Applications.

Model History

The first version of TAOS was installed at the CIMH in December 1994 and tested during 1995. CIMH uses TAOS/L in training Meteorological Officers throughout the region in the interpretation of NHC tropical storm forecasts. CIMH also provides guidance to National Meteorological Services in using the model for issuing storm surge and maximum wind warnings. CIMH is the base for TAOS within the Caribbean. Since the original installation of the TAOS, CDMP has continued to provide CIMH support for the use of the model in 1998. Experience with TAOS at CIMH prompted CDMP to undertake an upgrade of the model. Enhancements to the user interface, standardization of model output and further model calibration and verification were the focus of this upgrade, which included the incorporation of a new wave model, integration of a new display module for model output (using GrADS) and development of a utility for automatic creation of Maximum Envelopes of Water (MEOWs). Regional workshops on the use of TAOS/L were conducted at CIMH for meteorologists from throughout the region in 1997 and for model users (Belize, Campeche Mexico and Jamaica) in 1999. See the final report from the 1999 workshop for more information. In the fall of 1999, the topography/bathymetry database built into TAOS/L was updated and a document summarizing and depicting the data sources used for this database was created. TAOS/L use notes are available on the TAOS/L Technical Page.

Model Verification Results

Following a decision of the 17th RAIV meeting of the World Meteorological Organization in Guadeloupe in April 1995, NOAA undertook a comparison of TAOS, SLOSH and a French storm surge model. NOAA concluded that all three produce "reasonable" forecasts that are generally consistent with observations from actual storms.

Detailed verification of TAOS predictions against actual storm measurements shows that over 95 percent of the peak surges predicted by the model have an error of less than 15 per cent when compared to measured or observed values. Over half of the predictions were within 3.5 percent of the actual peak values. These validation results compare favorably with those of other currently accepted surge models.

Charles Watson of Watson Technical Consulting (WTC) developed the Caribbean-specific version TAOS for the CDMP. For more information on TAOS, contact Watson Technical Consulting.

CDMP home page: Project Contacts Page Last Updated: 10 February 2004