Reducing Disaster Risk by Managing Urban Land Use

Guidance Notes for Planners

• Éditeur: Asian Development Bank
• Année: 2016
• ISBN:
  9789292574765
• Sujet: Social Sciences
• Sous-sujet: Global Development Studies

This publication provides guidance for urban planners on how to use land use management-related tools they have at their disposal---land use planning, development control instruments, greenfield development, and urban redevelopment---to reduce disaster risk and contribute to strengthening urban resilience and sustainable urban development. The guidance provided in the document is further illustrated through case studies showing examples where urban land use management-related tools have been adopted to reduce disaster risk. It is hoped that this publication will support urban planners as a professional group to step up and embrace disaster risk reduction.

PHOTO: ADB

PHOTO: ADB

GUIDANCE NOTE 1: UNDERSTANDING DISASTER RISK

This note provides urban planners with guidance on how disaster risk assessment is undertaken: identifying hazards and understanding their characteristics, assessing the exposure and vulnerability of assets, and assessing disaster risk. While it is not the task of the urban planners to undertake such assessments by themselves, it is important for them to have a good understanding of what constitutes disaster risk; the process of assessing disaster risk; and, most importantly, how the results of the assessment can be used in the context of urban land use management.

KEY MESSAGES

Disaster risk is a function of probability of occurrence of hazards p(h), vulnerability v, and exposure e. It is expressed using the following formula:

Disaster risk = f(p(hi),v,e)

• Hazard characterizes the features of likely hazards, such as floods, earthquakes, tropical cyclones, or landslides, in a specific location in terms of frequency, intensity, and spatial occurrence, as well as their interlap.

• Vulnerability is a measure of the fragility of the assets at risk (physical characteristics and/or socioeconomic conditions) and how they perform given the intensity of hazard impact (whereby intensity includes attributes such as magnitude and duration).

• Exposure identifies the elements at risk in a specific location, such as size, composition, and density of the population, buildings, infrastructure, their cultural significance, and economic activity that could potentially be affected by the hazards.

Figure 1.1 shows a schematic diagram of examples of disaster risk in an urban setting.

Figure 1.1: Components of Disaster Risk in an Urban Setting

Source: Authors.

Understanding the spatial correlation between the multihazard landscape, on the one hand, and the vulnerability and exposure of the population, buildings, and infrastructure, on the other, will help urban planners undertake urban land use management-related decisions that will (i) reduce disaster risk in urban areas in the present and (ii) not increase urban disaster risk in the future. For example, an understanding of the characteristics of flooding in and around a city encourages the adoption of a land use policy that steers new development away from floodplains, restricts the use of wetlands and unstable slopes through development control regulations, prioritizes investments such as flood embankments, and informs stormwater drainage planning for the city.

KEY ACTIONS

For the successful application of disaster risk assessment in urban land use management:

Consider the question how do you want to use the results of the assessment?—the end use of the disaster risk assessment—and agree on its methodology and scope. Disaster risk assessment can vary in terms of objectives, scope, and methodology. Factors such as access to information, budget, and available technical capacity play an important role in determining the scope and methodology of the assessment. There is a wide range of tools and methodologies available to undertake disaster risk assessments (e.g., free open source tools vs. restricted commercial owner or operator tools, qualitative vs. quantitative, deterministic vs. probabilistic). Since no one size fits all, each city will need to determine what is most appropriate to its context. However, at the very least, for the disaster risk assessment to be useful for land use management purposes, the assessment must identify, categorize, and differentiate disaster risks spatially. Spatial analytical tools such as geographic information systems are particularly valuable.

Collaborate with specialist technical agencies, local universities, emergency management agencies, and development partners. This will help urban planners to become familiar with existing and/or planned initiatives on disaster risk assessment—their objectives, scope, and limitations; to communicate the types and scale of information required for land use management related decisions; and, where needed, to undertake and update assessments. Collaboration with a variety of specialist technical agencies to interpret the results of the risk assessment will help ensure that a wide range of disaster risk-related issues are addressed in a comprehensive manner.

LIKELY CHALLENGES

Uncertainties are inherent to disaster risk assessment, especially when modeling changes in the magnitude and intensity of extreme weather events, assessing flood risk, or assessing the impact of extreme and sudden events like large earthquakes. It is important to appreciate that uncertainties exists and discuss the implication for the results and decision making.

Data required for developing exposure database for the urban area and for undertaking vulnerability assessments may not always be available.

The public release of the disaster risk assessment outcomes can have significant effects on land and properties values. Thus, it is important to engage decision makers from the onset and use reputed national and/or local technical agencies (with inputs from international experts, where required) to demonstrate the credibility of the assessment results.

1.1 INTRODUCTION

Disaster risk can be characterized as a function of (i) the probability of occurrence of hazards of varying severity in a particular location, (ii) the people and physical assets that are situated in the location and exposed to the hazards, and (iii) the level of vulnerability of those people and assets to hazards.^1,2

For example, in an earthquake-prone urban area, disaster risk is a function of many factors including (i) the probability of ground shaking, slope failure, liquefaction, up- or downthrust, and seiching induced by an earthquake occurrence; (ii) the population, housing, infrastructure, and cultural and economic activity located in the area and thus exposed to the physical effects of the earthquake; and (iii) the level of vulnerability due to the physical characteristics of buildings and infrastructure (e.g., the vulnerability of a residential building is a factor of building height, layout, proximity to other structures, age of the building, choice of construction material, and standard of construction) as well as other socioeconomic conditions (poverty level, livelihood choices, gender equity, land tenure security, etc.) of the population.

In other words, it is not just the hazard level, but equally what is at risk (the exposure) and why (the vulnerability of population and assets), which in turn is largely dependent on development processes which drive the level of disaster impact. This is particularly true for urban areas. Each hazard type the city is exposed to—geophysical, hydrological, meteorological, and climatological (as well as biological and technological)—has its own risk-creating characteristics that produce spatial variations in vulnerability and exposure.

For an urban planner working on urban growth and development, it is critical, for the following reasons, to understand the spatial correlation between the evolving multihazard landscape and the elements (population, buildings, infrastructure, and businesses) that are/will be at risk:

Urban areas are developing at a rapid pace. The growth in population and physical assets in hazard-prone areas, lack of basic infrastructure and access to affordable land, and substandard construction of buildings and infrastructure increase the vulnerability and exposure of the urban population and physical assets to hazards.

Lack of awareness of disaster risk in rapidly growing urban areas. In many cases, the rapid growth in cities has taken place in a very short time frame compared to the return period of some hazards. These urban areas may not have experienced large-scale hazard events since they were established and, as a result, do not have an adequate understanding of the level of disaster risk.

Urban development can change the disaster risk profile. The process of urban development itself can change the risk profile in any given area, for example by altering drainage patterns or filling natural flood retention areas. Rapid urban growth may create new risks in areas that were not previously exposed, without the awareness of residents, or emergency response planners.

Climate change is expected to increase disaster risk. With climate change, the pattern of climate-related hazards is expected to change in terms of intensity, frequency, seasonality, and location. This may be accompanied by sea-level change, which will further exacerbate the trend of rising disaster losses in urban areas.

This requires assessing disaster risk and utilizing the findings of the assessment in decision making regarding urban land use management.

1.2 GETTING STARTED

In order to apply disaster risk assessment in urban land use management:

Collect information on existing disaster risk assessments. An important first step is to consult with technical agencies, local universities, emergency management agencies, and development partners and to collect information on disaster risk assessments that have already been undertaken for the city and the larger region. It is important to understand the purpose of any prior assessments (to raise awareness on disaster risk, to inform disaster risk reduction investment, to inform emergency contingency planning, etc.), their scope (single hazard or multihazard), methodology (deterministic or probabilistic), forms in which results were presented (maps, loss curves, average annual loss,³ probable maximum loss,⁴ etc.) scale, year of implementation, stakeholders and/or experts involved in undertaking the assessment, and application of assessment results.

Consult with relevant technical specialists: Consult with a range of hazard specialis...