How to Prepare a Risk Map

Preparation of Risk Maps - Technical Brief

Introduction

This document addresses the risk maps that resulted from the experience carried out in the emergency preparedness project in Peru. The methodology will have to be revised according to other more comprehensive risk reduction experiences and strategies that are being implemented institutionally but that lack instruments such as the one described here.

Conceptual approach

Risk

Risk is defined as the probability that people may suffer injuries or damages because of a disaster. Risk may be calculated, based on three elements: a) the frequency and severity of a threat, b) the vulnerability, and c) capacity of people, communities and institutions to respond to such a threat and recover from its impact.

Therefore, the greater the risk, the greater the vulnerability of a community and the lower its response and recovery capacity.

Risk map

The purpose of a risk map is to identify and classify areas, taking into account the probable damages that could occur as a result of a disaster.

What is a threat?

A threat is defined as the probability that a potentially destructive or damaging phenomenon or event may occur (earthquakes, "huaycos," floods, landslides, tsunamis, droughts, wars, epidemics), and impact on determined vulnerability conditions.

What is vulnerability?

Vulnerability is defined as the characteristics of individuals, groups, or societies that determine its degree of exposition to a threat or risk. Key characteristics include class, ethnicity, gender, disability, age, and condition.

The groups that are especially vulnerable are those for whom it is difficult to survive and to rebuild housing following a disaster.

File:P001b.jpg
Risk map prepared by a member of the community

Outline for the preparation of risk maps by using geographic information systems

How are threat maps prepared?

1. Initial inputs

2. Field trip

3. Preparation of threat maps

Actions that may raise our vulnerability

4. Analysis of the threat map

The threat map obtained in the previous step is made up of numbers that need to be reclassified to assign them qualitative values.

For example, the following table displays the numbers obtained in the threat map.

Quantitative Value	Qualitative Value
1	Low
2	Medium
3	High
4	Very high

Low:	Expresses minimal values and does not constitute a potential threat
Medium:	Expresses intermediate values and could constitute a potential threat
High:	Expresses high values and constitutes a threat
Very high:	Expresses very high values and constitutes an extreme threat

For example

A community which is located on a steep slope and receives a lot of precipitation in thesummer months is considered at a value of 4, whereas the same community in a slightly flatarea, but also receiving precipitation is considered at a value of 1.

5. Validation of the landslide map in workshop and preparation of the final version.

How are vulnerability maps prepared?

1. Initial inputs

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2. Field trip

3. Preparation of the vulnerability map

• Completion of the vulnerability forms. • Preparation of a database. • Preparation of the vulnerability map taking into consideration three aspects: • Accessibility to vehicles and transportation, telephone and radio communication. • Basic services in houses, such as electrical power, potable water, sewers, and construction materials of the houses (wood, thatch, tiles, and corrugated iron) • Capacity of local institutions (parishes, schools, municipalities, mothers' clubs, health stations, self-defence committees) • Based on the vulnerability variables, the formula that associates these variables toa 1 to 4 value range is generated.

Quantitative Value	Qualitative Value
1	Low
2	Medium
3	High
4	Very high

Low:	Expresses minimal values and does not constitute a potential threat
Medium:	Expresses intermediate values and could constitute a potential threat
High:	Expresses high values and constitutes a threat
Very high:	Expresses very high values and constitutes an extreme threat

For example

One of the vulnerability variables is the difficult access to communities. Roads are unpaved andonly four are suitable for motor vehicles, which gives those communities that only have unpavedunsuitable roads a value of 4. Another community located in a slightly flat area and also receiving precipitation is considered at avalue of 1.

4. Producing the vulnerability map

What are risk maps used for?

• Risk maps allow the identification of the location of the risks and threats.

• They offer authorities and organisations ideas, shared with the community and experts, to make decisions and know what the existing dangers and threats are.

• All local stakeholders take part, analyse, and allow us to understand their perception of the situations.

• Maps allow registering historical events that have negatively affected the community.

• They help to prepare for emergencies.

For more information: Practical Action Latin America Disaster Prevention and Local Governability Programme Av. Jorge Chavez 275 - Miraflores. Lima Perú Tel: (01) 447-5127/4467324/2429714

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