GIS and risk assessment

Ajay Lavakare
Managing Director
RMSI, Noida
ajayl@riskinc.com

Introduction
GIS technology is increasingly being used in spatial decision support systems. In the past few years, GIS emerged as a powerful risk assessment tool and is being put to use to assess risk to property and life stemming from natural hazards such as earthquakes, hurricanes, cyclones and floods. Manipulation, analysis, and graphic presentation of the risk and hazard data can be done within a GIS system, and because these data have associated location information which is also stored within the GIS, their spatial interrelationships can be determined and used in computer based risk assessment models. This assessment can be used by insurance companies to help them make decisions on their insurance policy rates, by land developers to make decisions on the feasibility of project sites, and by government planners for better disaster preparedness.

Risk Assessment
A fundamental principal of Risk Assessment is that risk due to natural catastrophes such as earthquakes, hurricanes and flood, is location dependent, and that it can be assessed within an acceptable range of uncertainty if reliable historical and location specific data is available. Risk assessment of natural catastrophes has two components-hazard and vulnerability. The hazard is a measure of the physical intensity of the peril (earthquake, wind, surge, etc.) at a particular location and the associated probabilities of these intensities. Hazard is location dependent. For example a location which is surrounded by seismic faults and has a weak surface geology has a higher hazard potential than a location for away from faults and with strong surface geology. Similarly, hurricane, hazard at a location near the coast and with a flat, bare terrain is far higher than at a location which is inland and has a rugged terrain.

Vulnerability is a measure of the damage that the peril can cause to the built environment (house, buildings, infrastructure and utilities) at that location. Manmade structure respond to different perils in different ways, depending on the design of their structural systems and methods of constructions.

Disaster preparedness programme in Andhra
Flood and cyclones play havoc with irrigation processes in the coastal areas of Andhra Pradesh. On the other hand, the Rayalseema and Telenagana regions with semiarid to arid climatic conditions are frequently affected by droughts. The worst affected are the rural people who are not adequately warned bout the impending disasters. Now, the Andhra Pradesh State Remote Sensing Applications Centre (APSRC) has developed a remote sensing application to overcome some of the problems that the state faces. The application areas include surface water, ground water, marine resources, geology and mines, energy, agriculture, soils, urban planning, roads, forestry, animal husbandry and environmental hazards.

GIS as a tool in risk assessment
GIS in conjunction with remote sensing and photogrammetry, can be used to identify hazards. Seismic faults and flood prone areas can be identified by scientists using GIS to analyse satellite image, aerial photos and field survey data.

Once the hazards have been identified, their representation can be stored conveniently in GIS databases. The information required for earthquake risk assessment includes the location and properties of seismic faults, surface geology, terrain slope, water table levels and inventories of epicentres and landslide occurrences. For hurricane risk, information on land use, land cover, coastline and distance from coast are important. Similarly topology data is required for flood assessment and storm surge analysis.

In addition new hazard layers can be generated within a GIS by combining hazard layers. For example, a landslide hazard layer can be generated by overlaying elevation, surface geology, water table level landslide inventory data, and liquefaction hazard can be generated in a GIS by overlaying geology with water table level data.

Inventory data can also be stored easily in a GIS database. Data on building stock, liveliness, utilities, etc. can be aggregated into manageable gographic regions such as census wards, pin codes, or larger administrative regions such as villages, talukas, and even districts. Using statistical functions available in GIS systems, the average value of various properties of different building classes can be computer (e.g. average monetary value of residential dwelling in particular village) and stored with their corresponding geographic regions in the GIS database.

The information retrieved by querying the GIS database serves as inputs for the risk assessment models. These risk assessment models can run both deterministic as well as probabilistic risk assessment. Deterministic risk assessment involves defining a disaster event and computing the damage associated with that event, whereas probabilistic risk assessment computes damage for different events, accounting for the probability of each event. Deterministic events could be defined using a GIS front-end system.

The result loss patterns ver regions and their associated uncertainties that are computed through this risk assessment can be mapped and again used for querying information through GIS applications. GIS technology provides a powerful tool for displaying outputs and permits users to “see” the geographic distribution of impacts from different peril scenarios and assumptions and allows the user to perform a quick graphical sensitivity analysis of the factors affecting the risk potential. A GIS based software system create the ideal framework to integrate the various components of the model