By Jacob Opadeyi PhD, Gabrielle Thongs MSc, Leah Fouchong BSc, Roxann Smith BSc, Desiree Joseph Bsc, Shelly Bradshaw BSc Department of Geomatics Engineering and Land Management The University of the West Indies St. Augustine Trinidad

Background The location of the Trinidad in the extreme south of the Caribbean means the country experiences a tropical marine climate. Floods and landslides are annual events associated with the rainy season in Trinidad and Tobago. Flooding and landslides are the most common and significant localized hazard.

Geraldo Greene, a 76-year old pensioner suffered a cruel death on Friday when a landslide destroyed part of his Santa Cruz home killing him in the process. Trinidad Express - Aug 6, 2001

Background Trinidad and Tobago faces a number of natural disaster issues Vulnerability assessment and risk mapping are the important first steps for any initiative for disaster reduction. A risk assessment is not only to find out where risk related problems are located, but also to quantitatively or qualitatively determine the significance of risks (Smith 2001, Greiving et al 2006)

Landslide and Flood Risk Mapping Objective To evaluate and rank the risk level to landslide of the resident population and the physical assets (buildings) of Trinidad. Input data Landslide susceptibility maps Population spatial distribution Building spatial distribution

Conceptual Design Areal Population Density Landslide Susceptibility Population Risk to Landslide Risk = Susceptibility + vulnerability (Population, Buildings) Areal Buildings Density Buildings Risk to Landslide Buildings & Population Risk to Landslide Inputs Results

Landslide Susceptibility

Instability Factors Tectonic Features Lithological Formation Slope Angle Road Network Drainage Network Land Use Rainfall

Cartographic Model - Landslide Ranking Weighting

Landslide Factor Ranking Instability Factors Classification Susceptibility Level Rank Road NetworkProximity (m) 0-100mVery High mHigh mHigh mModerate mLow mLow 2 >600mVery Low1

Landslide Factor Weighting: Scenario E Instability Factors Scenario E % Tectonic Features Lithological Formation Slope Angle Land Use Drainage Network Road Network Rainfall Total 101

Landslide Susceptibility Map Summation of land areas in each susceptibility class ClassesCOUNTArea by cellArea (ha)% of total Very Low 6159, ,000 61, Low 15534, , , Moderate 14014, , , High 8397, ,500 83, Very High 3522, ,500 35, Total , ,

Population Density Classification Scheme Population Density by ED per hectaresVulnerability level Very Low Low Moderate ,032High 1, ,874Very High

Building Density Classification Scheme Building Density By ED per hectaresVulnerability level 0 - 8Very Low Low Moderate High Very High

Vulnerability Population Vulnerability Class Building Vulnerability Class Very LowLowModerateHighVery High Very low Low Moderate High Very High Risk LevelRisk Value Very low<3<3 Low3-5 Moderate6 High7 Very High> 7

Single-Risk (Population) Map Single-Risk (Buildings) Map Multi-Risk (Buildings and population) Map Results: Landslide Risk Maps

Landslide Population Risk Assessment

Single Risk Classification Scheme Vulnerability Class Susceptibility Class Very LowLowModerateHighVery High Very low Low Moderate High Very High Risk LevelRisk Value Very low< 3 Low3-5 Moderate6 High7 Very High> 7

Landslide Population Risk (Sum of Land Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 32,3523,235, % Low 523,05652,305,6005, % Moderate 1,188,482118,848,20011, % High 1,485,898148,589,80014, % Very High 2,084,492208,449,20020, %

Landslide Building Risk Assessment

(Sum of Built-up Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 648,67964,867,9006, % Low 1,271,283127,128,30012, % Moderate 1,513,640151,364,00015, % High 1,249,585124,958,50012, % Very High 631,09363,109,3006, %

Landslide Multi-Risk Assessment: Building and Population

Multi-Risk Classification Scheme Vulnerability Class Susceptibility Class Very Low LowModerateHighVery High Very low Low Moderate High Very High Multi-Risk LevelRisk Value Very low< 6 Low6-7 Moderate8-9 High10-11 Very High> 12

Landslide Multi (Building & Population) Risk Assessment (Sum of Land Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 505,08850,508,8005, % Low 919,68591,968,5009, % Moderate 1,197,265119,726,50011, % High 1,201,305120,130,50012, % Very High 1,490,937149,093,70014, %

Flood Risk Mapping Objective To evaluate and rank the risk level to flooding of the resident population and the physical assets (buildings) of Trinidad Input data Flood susceptibility Map Population spatial distribution Building spatial distribution

Conceptual Design Areal Population Density Flood Susceptibility Population Risk to Flooding Risk = Hazard Susceptibility + Vulnerability (Population, Buildings) Areal Buildings Density Buildings Risk to Flooding Buildings & Population Risk to Flooding Inputs Results

Flood Factors Rainfall (mm) Slope (%) Land Use Drainage density Road (% each watershed) Elevation (m)

Cartographic Model - Flood Ranking Weighting

Flood Susceptibility Map Summation of land areas in each susceptibility class ClassesCOUNTArea by cellArea (ha)% of total Very Low 2,327, ,791,000 23, Low 9,959, ,919,500 99, Moderate 16,847,280 1,684,728, , High 13,471,559 1,347,155, , Very High 5,304, ,496,200 53, Total 4,791,090, ,

Population Vulnerability Classification Scheme Population Density By ED per hectaresVulnerability level Very Low Low Moderate ,032High 1, ,874Very High

Building Vulnerability Classification Scheme Building Density By ED per hectaresVulnerability level 0 - 8Very Low Low Moderate High Very High

Single-Risk (Population) Map Single-Risk (Buildings) Map Multi-Risk (Buildings and population) Map Results: flood risk maps

Flood Population Risk Assessment

Single Risk Classification Scheme Population Vulnerability Class Susceptibility Class Very LowLowModerateHighVery High Very low Low Moderate High Very High Risk LevelRisk Class Very low< 4 Low4-5 Moderate6 High7 Very High> 7

Flood Population Risk (Sum of Land Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 1,194, ,483,400 11, % Low 1,687, ,785,800 16, % Moderate 1,644, ,457,800 16, % High 696,494 69,649,400 6, % Very High 125,510 12,551,000 1, %

Flood Building Risk Assessment

(Sum of Land Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 1,405, ,568,000 14, % Low 1,716, ,619,600 17, % Moderate 1,496, ,609,400 14, % High 625,967 62,596,700 6, % Very High 105,337 10,533,700 1, %

Flood Multi-Risk Assessment: Building and Population

Multi-Risk Classification Scheme Vulnerability Class Susceptibility Class Very Low LowModerateHighVery High Very low Low Moderate High Very High Multi-Risk LevelRisk Value Very low< 6 Low6-7 Moderate8-9 High10-11 Very High> 12

Flood Multi (Building & Population) Risk Assessment (Sum of Land Area under each risk level) Risk Level Number of cellsArea (m2)Area (HA) % of Trinidad urban land mass Very Low 925,747 92,574,700 9, % Low 1,467, ,764,100 14, % Moderate 1,334, ,422,000 13, % High 1,402, ,291,200 14, % Very High 218,754 21,875,400 2, %

Uses Development control and planning Disaster mitigation planning Disaster management Policy formulation Law reforms Site analysis Review of insurance premium

Users Physical Planning Offices Non-Governmental Organizations Environmental Agencies Works Departments Utility Companies Insurance Agencies National Disaster Offices Security and Protective Services Lending Agencies Meteorology and Hydrology Departments Educational Institutions Land Developers General Public Foreign Investors

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