July 21, 2012

Extreme Events and Disasters

Intergovernmental Panel on Climate Change

Impacts of Heat Waves in Urban Areas in Europe

Factors affecting exposure and vulnerability include
  • age,
  • pre-existing health status,
  • level of outdoor activity,
  • socioeconomic factors including poverty and social isolation,
  • access to and use of cooling,
  • physiological and behavioral adaptation of the population, and
  • urban infrastructure.

Options for risk management and adaptation …

Low-regrets options …
  • Early warning systems that reach particularly vulnerable groups (eg, the elderly)
  • Vulnerability mapping and corresponding measures
  • Public information on what to do during heat waves, including behavioral advice
  • Use of social care networks to reach vulnerable groups

Specific adjustments in strategies, policies, and measures informed by trends in heat waves include
  • awareness raising of heat waves as a public health concern;
  • changes in urban infrastructure and land use planning, for example, increasing urban green space;
  • changes in approaches to cooling for public facilities; and
  • adjustments in energy generation and transmission infrastructure.

Increasing Losses from Hurricanes in the USA and the Caribbean

Exposure and vulnerability are increasing due to growth in population and increase in property values, particularly along the Gulf and Atlantic coasts of the United States.
Some of this increase has been offset by improved building codes.

Options for risk management and adaptation …

Low-regrets options …
  • Adoption and enforcement of improved building codes
  • Improved forecasting capacity and implementation of improved early warning systems (including evacuation plans and infrastructures)
  • Regional risk pooling

In the context of high underlying variability and uncertainty regarding trends, options can include emphasizing adaptive management involving learning and flexibility (eg, Cayman Islands National Hurricane Committee).
(Table SPM.1, p 17)

Confidence, Evidence, Agreement and Probability

Based on the Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties, this Summary for Policymakers relies on two metrics for communicating the degree of certainty in key findings …
  • Confidence in the validity of a finding, based on the type, amount, quality, and consistency of evidence … and the degree of agreement.
    Confidence is expressed qualitatively.
  • Quantified measures of uncertainty in a finding expressed probabilistically (based on statistical analysis of observations or model results, or expert judgment). …

Direct comparisons between assessment of uncertainties in findings in this report and those in the IPCC Fourth Assessment Report are difficult if not impossible, because of
  • the application of the revised guidance note on uncertainties …
  • the availability of new information, improved scientific understanding, continued analyses of data and models, and
  • specific differences in methodologies applied in the assessed studies. …

The following summary terms are used to describe
  • the available EVIDENCE: limited, medium, or robust; [and]
  • the degree of AGREEMENT: low, medium, or high.
A level of CONFIDENCE is expressed using five qualifiers: very low [low agreement, limited evidence], low, medium, high, and very high [high agreement, robust evidence].

Unless otherwise indicated, high or very high confidence is associated with findings for which an author team has assigned a likelihood term.

TermLikelihood of the Outcome
Virtually certain99–100% probability
Very Likely90–100% probability
Likely66–100% probability
About as likely as not33–66% probability
Unlikely0–33% probability
Very unlikely0–10% probability
Exceptionally unlikely0–1% probability




Past Experience

Future Changes

Managing Changing Risks


  • Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Summary for Policymakers (SREX-SPM), Working Groups I & II, June, 2012.


    Exposure and vulnerability are key determinants of disaster risk and of impacts when risk is realized. …

    Extreme and non-extreme weather or climate events affect vulnerability to future extreme events by modifying resilience, coping capacity, and adaptive capacity.

    (p 4)

    A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of extreme weather and climate events, and can result in unprecedented extreme weather and climate events.


    Exposure and Vulnerability

    Exposure and vulnerability are dynamic, varying across temporal and spatial scales, and depend on economic, social, geographic, demographic, cultural, institutional, governance, and environmental factors (high confidence). …

    Settlement patterns, urbanization, and changes in socioeconomic conditions have all influenced observed trends in exposure and vulnerability to climate extremes (
    high confidence).
    (p 5)

    Climate Extremes and Impacts

    There is evidence from observations gathered since 1950 of change in some extremes.
    Confidence in observed changes in extremes depends on the quality and quantity of data and the availability of studies analyzing these data, which vary across regions and for different extremes.
    Assigning ‘low confidence’ in observed changes in a specific extreme on regional or global scales neither implies nor excludes the possibility of changes in this extreme. …

    It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, at the global scale …
    It is likely that these changes have also occurred at the continental scale in North America, Europe, and Australia.
    There is medium confidence in a warming trend in daily temperature extremes in much of Asia. …
    In many [regions over the globe] there is medium confidence that the length or number of warm spells or heat waves has increased.

    There have been statistically significant trends in the number of heavy precipitation events in some regions.
    It is likely that more of these regions have experienced increases than decreases …

    It is likely that there has been a poleward shift in the main Northern and Southern Hemisphere extratropical storm tracks. …

    There is medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, for example, in central North America and northwestern Australia.
    (p 6)

    It is likely that there has been an increase in extreme coastal high water related to increases in mean sea level. …
    It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures at the global scale.
    There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation at the global scale.
    It is likely that there has been an anthropogenic influence on increasing extreme coastal high water due to an increase in mean sea level.

    Disaster Losses

    Economic losses from weather- and climate-related disasters have increased, but with large spatial and interannual variability (high confidence, based on high agreement, medium evidence).
    Estimates of annual losses have ranged since 1980 from a few US$ billion to above 200 billion (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina).
    Loss estimates are lower-bound estimates because many impacts, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and monetize …
    Impacts on the informal or undocumented economy as well as indirect economic effects can be very important in some areas and sectors, but are generally not counted in reported estimates of losses.

    Economic, including insured, disaster losses associated with weather, climate, and geophysical events are higher in developed countries.
    Fatality rates and economic losses expressed as a proportion of gross domestic product (GDP) are higher in developing countries (high confidence).

    During the period from 1970 to 2008, over 95% of deaths from natural disasters occurred in developing countries. …
    During the period from 2001 to 2006, losses amounted to
    • about 1% of GDP for middle-income countries …
    • about 0.3% of GDP for low-income countries and
    • less than 0.1% of GDP for high-income countries
    based on limited evidence.
    In small exposed countries, particularly small island developing states, losses [have exceeded] 1% in many cases and 8% in the most extreme cases …

    Increasing exposure of people and economic assets has been the major cause of long-term increases in economic losses from weather- and climate-related disasters (high confidence).
    Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded (
    high agreement, medium evidence).
    (p 7)


    The severity of the impacts of climate extremes depends strongly on the level of the exposure and vulnerability to these extremes (high confidence).

    Trends in exposure and vulnerability are major drivers of changes in disaster risk (
    high confidence).
    Vulnerability reduction is a core common element of adaptation and disaster risk management.

    Development practice, policy, and outcomes are critical to shaping disaster risk, which may be increased by shortcomings in development (high confidence).

    Data on disasters and disaster risk reduction are lacking at the local level, which can constrain improvements in local vulnerability reduction (
    high agreement, medium evidence).

    Inequalities influence local coping and adaptive capacity, and pose disaster risk management and adaptation challenges from the local to national levels (
    high agreement, robust evidence).

    Humanitarian relief is often required when disaster risk reduction measures are absent or inadequate (
    high agreement, robust evidence).

    Post-disaster recovery and reconstruction provide an opportunity for reducing weather- and climate-related disaster risk and for improving adaptive capacity (
    high agreement, robust evidence).
    An emphasis on rapidly rebuilding houses, reconstructing infrastructure, and rehabilitating livelihoods often leads to recovering in ways that recreate or even increase existing vulnerabilities, and that preclude longer-term planning and policy changes for enhancing resilience and sustainable development. …

    Risk sharing and transfer mechanisms at local, national, regional, and global scales can increase resilience to climate extremes (medium confidence).
    (p 7)

    Attention to the temporal and spatial dynamics of exposure and vulnerability is particularly important given that the design and implementation of adaptation and disaster risk management strategies and policies can reduce risk in the short term, but may increase exposure and vulnerability over the longer term (high agreement, medium evidence).
    For instance, dike systems can reduce flood exposure by offering immediate protection, but also encourage settlement patterns that may increase risk in the long term. …

    National systems are at the core of countries’ capacity to meet the challenges of observed and projected trends in exposure, vulnerability, and weather and climate extremes (high agreement, robust evidence).

    Closer integration of disaster risk management and climate change adaptation, along with the incorporation of both into local, sub-national, national, and international development policies and practices, could provide benefits at all scales (
    high agreement, medium evidence).


    Climate Extremes and Impacts

    Confidence in projecting changes in the direction and magnitude of climate extremes depends on many factors, including the type of extreme, the region and season, the amount and quality of observational data, the level of understanding of the underlying processes, and the reliability of their simulation in models.
    Projected changes in climate extremes under different emissions scenarios … are relatively small compared to natural climate variability over [the coming two to three decades.]
    Even the sign of projected changes in some climate extremes over this time frame is uncertain.
    For projected changes by the end of the 21st century, either model uncertainty or uncertainties associated with emissions scenarios used becomes dominant, depending on the extreme.
    Low-probability, high-impact changes associated with the crossing of poorly understood climate thresholds cannot be excluded, given the transient and complex nature of the climate system.
    (p 9)

    Models project substantial warming in temperature extremes by the end of the 21st century.
    It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur in the 21st century at the global scale.
    It is very likely that the length, frequency, and/or intensity of warm spells or heat waves will increase over most land areas.

    [A] 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century in most regions …
    The 1-in-20 year extreme daily maximum temperature … will likely increase by about 1°C to 3°C by the mid-21st century and by about 2°C to 5°C by the late 21st century …

    It is likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in the 21st century over many areas of the globe. …
    Heavy rainfalls associated with tropical cyclones are likely to increase …
    There is medium confidence that, in some regions, increases in heavy precipitation will occur despite projected decreases in total precipitation …
    [A] 1-in-20 year annual maximum daily precipitation amount is likely to become a 1-in-5 to 1-in-15 year event by the end of the 21st century in many regions …

    Average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins.
    It is
    likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged.
    There is medium confidence that there will be a reduction in the number of extratropical cyclones averaged over each hemisphere [and] in a projected poleward shift of extratropical storm tracks.

    There is medium confidence that droughts will intensify in the 21st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration.
    [Affected regions include] southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa.

    Projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods. …
    There is medium confidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases in local flooding in some catchments or regions.
    (p 11)

    It is very likely that mean sea level rise will contribute to upward trends in extreme coastal high water levels in the future.
    There is high confidence that locations currently experiencing adverse impacts such as coastal erosion and inundation will continue to do so …

    There is high confidence that changes in heat waves, glacial retreat, and/or permafrost degradation will affect high mountain phenomena such as slope instabilities, movements of mass, and glacial lake outburst floods.
    [And] that changes in heavy precipitation will affect landslides in some regions.

    There is low confidence in projections of changes in large-scale patterns of natural climate variability [such as monsoons and ENSO].
    (p 13)

    Human Impacts and Disaster Losses

    Extreme events will have greater impacts on sectors with closer links to climate, such as water, agriculture and food security, forestry, health, and tourism.
    [While] it is not currently possible to reliably project specific changes at the catchment scale, there is high confidence that changes in climate have the potential to seriously affect water management systems.

    In many regions, the main drivers of future increases in economic losses due to some climate extremes will be socioeconomic in nature (medium confidence, based on medium agreement, limited evidence). …

    Increases in exposure will result in higher direct economic losses from tropical cyclones.
    Losses will also depend on future changes in tropical cyclone frequency and intensity (
    high confidence).
    Overall losses due to extratropical cyclones will also increase, with possible decreases or no change in some areas (medium confidence).
    Although future flood losses in many locations will increase in the absence of additional protection measures (high agreement, medium evidence), the size of the estimated change is highly variable …

    Disasters associated with climate extremes influence population mobility and relocation, affecting host and origin communities (medium agreement, medium evidence).


    Measures that provide benefits under current climate and a range of future climate change scenarios, called low-regrets measures, are available starting points for addressing projected trends in exposure, vulnerability, and climate extremes.
    They have the potential to offer benefits now and lay the foundation for addressing projected changes (high agreement, medium evidence).
    Many of these low-regrets strategies produce co-benefits … such as improvements in livelihoods, human well-being, and biodiversity conservation …
    Potential low-regrets measures include
    • early warning systems;
    • risk communication between decisionmakers and local citizens;
    • sustainable land management, including land use planning; and
    • ecosystem management and restoration. …
    • improvements to health surveillance,
    • water supply, sanitation, and irrigation and drainage systems;
    • climate-proofing of infrastructure;
    • development and enforcement of building codes; and
    • better education and awareness.
    (p 14)

    Effective risk management generally involves a portfolio of actions to reduce and transfer risk and to respond to events and disasters, as opposed to a singular focus on any one action or type of action (high confidence).
    Such integrated approaches are more effective when they are informed by and customized to specific local circumstances (high agreement, robust evidence).
    Successful strategies include a combination of
    • hard infrastructure-based responses and
    • soft solutions such as individual and institutional capacity building and ecosystem-based responses.

    Multi-hazard risk management approaches provide opportunities to reduce complex and compound hazards (high agreement, robust evidence).
    Considering multiple types of hazards reduces the likelihood that risk reduction efforts targeting one type of hazard will increase exposure and vulnerability to other hazards, in the present and future.

    Opportunities exist to create synergies in international finance for disaster risk management and adaptation to climate change, but these have not yet been fully realized (high confidence). …
    Technology transfer and cooperation to advance disaster risk reduction and climate change adaptation are important.
    Coordination … between these two fields has been lacking [leading] to fragmented implementation.

    Stronger efforts at the international level do not necessarily lead to substantive and rapid results at the local level (high confidence).
    There is room for improved integration across scales from international to local.

    Integration of local knowledge with additional scientific and technical knowledge can improve disaster risk reduction and climate change adaptation (high agreement, robust evidence). …
    [Improvements] in the availability of human and financial capital and of disaster risk and climate information customized for local stakeholders can enhance community-based adaptation (medium agreement, medium evidence).

    Appropriate and timely risk communication is critical for effective adaptation and disaster risk management (high confidence). …

    An iterative process of monitoring, research, evaluation, learning, and innovation can reduce disaster risk and promote adaptive management in the context of climate extremes (
    high agreement, robust evidence).
    Adaptation efforts benefit from iterative risk management strategies because of the complexity, uncertainties, and long time frame associated with climate change (high confidence).

    Table SPM.1 presents examples of how observed and projected trends in exposure, vulnerability, and climate extremes can inform risk management and adaptation strategies, policies, and measures.
    (p 15)


    … The confidence in projected changes in climate extremes at local scales is often more limited than the confidence in projected regional and global changes.
    This limited confidence in changes places a focus on low-regrets risk management options that aim to reduce exposure and vulnerability and to increase resilience and preparedness for risks …
    Higher-confidence projected changes in climate extremes … can inform more targeted adjustments in strategies, policies, and measures. …

    Inundation related to extreme sea levels in tropical small island developing states

    Small island states in the Pacific, Indian, and Atlantic Oceans, often with low elevation, are particularly vulnerable to rising sea levels and impacts such as erosion, inundation, shoreline change, and saltwater intrusion into coastal aquifers.
    These impacts can result in ecosystem disruption, decreased agricultural productivity, changes in disease patterns, economic losses such as in tourism industries, and population displacement – all of which reinforce vulnerability to extreme weather events. …

    Options for risk management and adaptation …

    Low-regrets options that reduce exposure and vulnerability across a range of hazard trends:
    • Maintenance of drainage systems
    • Well technologies to limit saltwater contamination of groundwater
    • Improved early warning systems
    • Regional risk pooling
    • Mangrove conservation, restoration, and replanting

    Specific adaptation options include, for instance, rendering national economies more climate-independent and adaptive management involving iterative learning.
    In some cases there may be a need to consider relocation, for example, for atolls where storm surges may completely inundate them.

    Flash floods in informal settlements in Nairobi, Kenya

    Rapid expansion of poor people living in informal settlements around Nairobi has led to houses of weak building materials being constructed immediately adjacent to rivers and to blockage of natural drainage areas, increasing exposure and vulnerability. …

    Options for risk management and adaptation …

    Low-regrets options …
    • Strengthening building design and regulation
    • Poverty reduction schemes
    • City-wide drainage and sewerage improvements
    The Nairobi Rivers Rehabilitation and Restoration Programme includes installation of riparian buffers, canals, and drainage channels and clearance of existing channels; attention to climate variability and change in the location and design of wastewater infrastructure; and environmental monitoring for flood early warning.
    (p 16)

    Droughts in the context of food security in West Africa

    Less advanced agricultural practices render region vulnerable to increasing variability in seasonal rainfall, drought, and weather extremes.
    Vulnerability is exacerbated by population growth, degradation of ecosystems, and overuse of natural resources, as well as poor standards for health, education, and governance.

    Options for risk management and adaptation …

    Low-regrets options …
    • Traditional rain and groundwater harvesting and storage systems
    • Water demand management and improved irrigation efficiency measures
    • Conservation agriculture, crop rotation, and livelihood diversification
    • Increasing use of drought-resistant crop varieties
    • Early warning systems integrating seasonal forecasts with drought projections, with improved communication involving extension services
    • Risk pooling at the regional or national level
    (p 17)

    Implications for Sustainable Development

    Actions that range from incremental steps to transformational changes are essential for reducing risk from climate extremes (high agreement, robust evidence).
    Where vulnerability is high and adaptive capacity low, changes in climate extremes can make it difficult for systems to adapt sustainably without transformational changes. …

    Social, economic, and environmental sustainability can be enhanced by disaster risk management and adaptation approaches.
    A prerequisite for sustainability in the context of climate change is addressing the underlying causes of vulnerability, including the structural inequalities that create and sustain poverty and constrain access to resources (
    medium agreement, robust evidence). …

    The most effective adaptation and disaster risk reduction actions are those that offer development benefits in the relatively near term, as well as reductions in vulnerability over the longer term (
    high agreement, medium evidence). …

    Progress toward resilient and sustainable development in the context of changing climate extremes can benefit from questioning assumptions and paradigms and stimulating innovation to encourage new patterns of response (
    medium agreement, robust evidence).
    Successfully addressing disaster risk, climate change, and other stressors often involves
    • embracing broad participation in strategy development,
    • the capacity to combine multiple perspectives, and
    • contrasting ways of organizing social relations.

    The interactions among climate change mitigation, adaptation, and disaster risk management may have a major influence on resilient and sustainable pathways (high agreement, limited evidence).
    (p 18)

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