IPCC_Managing Risks of Extreme Events.pdf - Climate Access

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Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentChapter 3threshold perspective (e.g., a 40°C threshold for midday temperature inthe mid-latitudes).In the scientific literature, several aspects are considered in the definitionand analysis of climate extremes (Box 3-1).3.1.3. Compound (Multiple) EventsIn climate science, compound events can be (1) two or more extremeevents occurring simultaneously or successively, (2) combinations ofextreme events with underlying conditions that amplify the impact ofthe events, or (3) combinations of events that are not themselvesextremes but lead to an extreme event or impact when combined. Thecontributing events can be of similar (clustered multiple events) ordifferent type(s). There are several varieties of clustered multiple events,such as tropical cyclones generated a few days apart with the samepath and/or intensities, which may occur if there is a tendency forpersistence in atmospheric circulation and genesis conditions. Examplesof compound events resulting from events of different types arevaried – for instance, high sea level coinciding with tropical cyclonelandfall (Section 3.4.4), or cold and dry conditions (e.g., the MongolianDzud, see Case Study 9.2.4), or the impact of hot events and droughtson wildfire (Case Study 9.2.2), or a combined risk of flooding from sealevel surges and precipitation-induced high river discharge (Svenssonand Jones, 2002; Van den Brink et al., 2005). Compound events can evenresult from ‘contrasting extremes’, for example, the projected occurrenceof both droughts and heavy precipitation events in future climate insome regions (Table 3-3).Impacts on the physical environment (Section 3.5) are often the resultof compound events. For instance, floods will more likely occur oversaturated soils (Section 3.5.2), which means that both soil moisturestatus and precipitation intensity play a role. The wet soil may itself bethe result of a number of above-average but not necessarily extremeprecipitation events, or of enhanced snow melt associated withtemperature anomalies in a given season. Similarly, droughts are theresult of pre-existing soil moisture deficits and of the accumulation ofprecipitation deficits and/or evapotranspiration excesses (Box 3-3), notall (or none) of which are necessarily extreme for a particular droughtevent when considered in isolation. Also, impacts on human systems orecosystems (Chapter 4) can be the results of compound events, forexample, in the case of health-related impacts associated with combinedtemperature and humidity conditions (Box 3-1).Although compound events can involve causally unrelated events, thefollowing causes may lead to a correlation between the occurrence ofextremes (or their impacts):1) A common external forcing factor for changing the probability ofthe two events (e.g., regional warming, change in frequency orintensity of El Niño events)2) Mutual reinforcement of one event by the other and vice versa dueto system feedbacks (Section 3.1.4)3) Conditional dependence of the occurrence or impact of one eventon the occurrence of another event (e.g., extreme soil moisture levelsand precipitation conditions for floods, droughts, see above).Changes in one or more of these factors would be required for a changingclimate to induce changes in the occurrence of compound events.Unfortunately, investigation of possible changes in these factors hasreceived little attention. Also, much of the analysis of changes ofextremes has, up to now, focused on individual extremes of a singlevariable. However, recent literature in climate research is starting toconsider compound events and explore appropriate methods for theiranalysis (e.g., Coles, 2001; Beirlant et al., 2004; Benestad and Haugen,2007; Renard and Lang, 2007; Schölzel and Friederichs, 2008; Beniston,2009b; Tebaldi and Sanso, 2009; Durante and Salvadori, 2010).3.1.4. FeedbacksA special case of compound events is related to the presence of feedbackswithin the climate system, that is, mutual interaction between severalclimate processes, which can either lead to a damping (negative feedback)or enhancement (positive feedback) of the initial response to a givenforcing (see also ‘climate feedback’ in the Glossary). Feedbacks can playan important role in the development of extreme events, and in somecases two (or more) climate extremes can mutually strengthen oneanother. One example of positive feedback between two extremes is thepossible mutual enhancement of droughts and heat waves in transitionalregions between dry and wet climates. This feedback has been identifiedas having an influence on projected changes in temperature variabilityand heat wave occurrence in Central and Eastern Europe and theMediterranean (Seneviratne et al., 2006a; Diffenbaugh et al., 2007), andpossibly also in Britain, Eastern North America, the Amazon, and EastAsia (Brabson et al., 2005; Clark et al., 2006). Further results also suggestthat it is a relevant factor for past heat waves and temperatureextremes in Europe and the United States (Durre et al., 2000; Fischer etal., 2007a,b; Hirschi et al., 2011). Two main mechanisms that have beensuggested to underlie this feedback are: (1) enhanced soil drying duringheat waves due to increased evapotranspiration (as a consequence ofhigher vapor pressure deficit and higher incoming radiation); and (2)higher relative heating of the air from sensible heat flux when soilmoisture deficit starts limiting evapotranspiration/latent heat flux (e.g.,Seneviratne et al., 2010). Additionally, there may also be indirect and/ornon-local effects of dryness on heat waves through, for example,changes in circulation patterns or dry air advection (e.g., Fischer et al.,2007a; Vautard et al., 2007; Haarsma et al., 2009). However, thestrength of these feedbacks is still uncertain in current climate models(e.g., Clark et al., 2010), in particular if additional feedbacks withprecipitation (e.g., Koster et al., 2004b; Seneviratne et al., 2010) andwith land use and land cover state and changes (e.g., Lobell et al., 2008;Pitman et al., 2009; Teuling et al., 2010) are considered. Also, feedbacksbetween trends in snow cover and changes in temperature extremes havebeen highlighted as being relevant for projections (e.g., Kharin et al.,2007; Orlowsky and Seneviratne, 2011). Feedbacks with soil moisture118
Chapter 3Changes in Climate Extremes and their Impacts on the Natural Physical EnvironmentTable 3-1 | Overview of considered extremes and summary of observed and projected changes at a global scale. Regional details on observed and projected changes in temperatureand precipitation extremes are provided in Tables 3-2 and 3-3. Extremes (e.g., cold/warm days/nights, heat waves, heavy precipitation events) are defined with respect to late 20thcenturyclimate (see also Box 3-1 for discussion of reference period).Observed Changes (since 1950)Attribution of ObservedChangesProjected Changes (up to 2100) withRespect to Late 20th CenturyWeatherandClimateVariablesTemperature(Section 3.3.1)Precipitation(Section 3.3.2)Very likely decrease in number of unusually cold daysand nights at the global scale. Very likely increase innumber of unusually warm days and nights at theglobal scale. Medium confidence in increase in lengthor number of warm spells or heat waves in many (butnot all) regions. Low or medium confidence in trends intemperature extremes in some subregions due eitherto lack of observations or varying signal withinsubregions. [Regional details in Table 3-2]Likely statistically significant increases in the numberof heavy precipitation events (e.g., 95th percentile) inmore regions than those with statistically significantdecreases, but strong regional and subregionalvariations in the trends. [Regional details in Table 3-2]Likely anthropogenic influence ontrends in warm/cold days/nights atthe global scale. No attribution oftrends at a regional scale with afew exceptions.Medium confidence thatanthropogenic influences havecontributed to intensification ofextreme precipitation at the globalscale.Virtually certain decrease in frequency and magnitudeof unusually cold days and nights at the global scale.Virtually certain increase in frequency and magnitudeof unusually warm days and nights at the global scale.Very likely increase in length, frequency, and/orintensity of warm spells or heat waves over most landareas. [Regional details in Table 3-3]Likely increase in frequency of heavy precipitationevents or increase in proportion of total rainfall fromheavy falls over many areas of the globe, in particularin the high latitudes and tropical regions, and inwinter in the northern mid-latitudes. [Regional detailsin Table 3-3]Winds(Section 3.3.3)Low confidence in trends due to insufficient evidence.Low confidence in the causes oftrends due to insufficient evidence.Low confidence in projections of extreme winds (withthe exception of wind extremes associated withtropical cyclones).PhenomenaRelated toWeather andClimateExtremesMonsoons(Section 3.4.1)El Niño andother Modes ofVariability(Sections 3.4.2and 3.4.3)Low confidence in trends because of insufficientevidence.Medium confidence in past trends toward morefrequent central equatorial Pacific El Niño-SouthernOscillation (ENSO) events.Insufficient evidence for more specific statements onENSO trends.Likely trends in Southern Annular Mode (SAM).Low confidence due to insufficientevidence.Likely anthropogenic influence onidentified trends in SAM. 1Anthropogenic influence on trendsin North Atlantic Oscillation (NAO)are about as likely as not. Noattribution of changes in ENSO.Low confidence in projected changes in monsoons,because of insufficient agreement between climatemodels.Low confidence in projections of changes in behaviorof ENSO and other modes of variability because ofinsufficient agreement of model projections.TropicalCyclones(Section 3.4.4)ExtratropicalCyclones(Section 3.4.5)Low confidence that any observed long-term (i.e., 40years or more) increases in tropical cyclone activity arerobust, after accounting for past changes in observingcapabilities.Likely poleward shift in extratropical cyclones.Low confidence in regional changes in intensity.Low confidence in attribution ofany detectable changes in tropicalcyclone activity to anthropogenicinfluences (due to uncertainties inhistorical tropical cyclones record,incomplete understanding ofphysical mechanisms, and degreeof tropical cyclone variability).Medium confidence in ananthropogenic influence onpoleward shift.Likely decrease or no change in frequency of tropicalcyclones.Likely increase in mean maximum wind speed, butpossibly not in all basins.Likely increase in heavy rainfall associated withtropical cyclones.Likely impacts on regional cyclone activity but lowconfidence in detailed regional projections due to onlypartial representation of relevant processes in currentmodels.Medium confidence in a reduction in the numbers ofmid-latitude storms.Medium confidence in projected poleward shift ofmid-latitude storm tracks.Impacts onPhysicalEnvironmentDroughts(Section 3.5.1)Medium confidence that some regions of the worldhave experienced more intense and longer droughts,in particular in southern Europe and West Africa, butopposite trends also exist. [Regional details in Table3-2]Medium confidence thatanthropogenic influence hascontributed to some observedchanges in drought patterns.Low confidence in attribution ofchanges in drought at the level ofsingle regions due to inconsistentor insufficient evidence.Medium confidence in projected increase in durationand intensity of droughts in some regions of theworld, including southern Europe and theMediterranean region, central Europe, central NorthAmerica, Central America and Mexico, northeastBrazil, and southern Africa.Overall low confidence elsewhere because ofinsufficient agreement of projections.[Regional details in Table 3-3]Floods(Section 3.5.2)Limited to medium evidence available to assessclimate-driven observed changes in the magnitudeand frequency of floods at regional scale.Furthermore, there is low agreement in this evidence,and thus overall low confidence at the global scaleregarding even the sign of these changes.High confidence in trend toward earlier occurrence ofspring peak river flows in snowmelt- and glacier-fedrivers.Low confidence that anthropogenicwarming has affected themagnitude or frequency of floods ata global scale.Medium confidence to highconfidence in anthropogenicinfluence on changes in somecomponents of the water cycle(precipitation, snowmelt) affectingfloods.Low confidence in global projections of changes inflood magnitude and frequency because of insufficientevidence.Medium confidence (based on physical reasoning)that projected increases in heavy precipitation wouldcontribute to rain-generated local flooding in somecatchments or regions.Very likely earlier spring peak flows in snowmelt- andglacier-fed rivers.Continued next page119
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MANAGING THE RISKS OF EXTREMEEVENTS
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Managing the Risks of Extreme Event
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I Foreword and Preface
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Prefacein understanding and managin
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Summary for PolicymakersBox SPM.1 |
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Summary for PolicymakersB.or sub-na
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Summary for PolicymakersIt is likel
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Summary for Policymakersmicro-insur
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Summary for PolicymakersIt is very
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Summary for PolicymakersOther low-r
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Summary for PolicymakersTable SPM.1
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Summary for PolicymakersBox SPM.2 |
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III Chapters 1 to 9
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Climate Change: New Dimensions in D
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Determinants of Risk: Exposure and
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Managing the Risks from Climate Ext
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National Systems for Managing the R
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Managing the Risks: International L
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Toward a Sustainable and Resilient
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Case StudiesChapter 9Table of Conte
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Case StudiesChapter 99.1. Introduct
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Case StudiesChapter 9••••
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ANNEXI Authors and Expert Reviewers
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Annex IAuthors and Expert Reviewers
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ANNEXIIGlossary of TermsThis annex
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Annex IIGlossary of Termswater vapo
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Annex IIGlossary of Termsdrought, a
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Annex IIGlossary of TermsImpactsEff
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Annex IIGlossary of Termsforcing is
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ANNEXIIIAcronyms565
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Annex IIIAcronymsNAMNAONAPANaTechND
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ANNEXIVList of Major IPCC Reports56
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Annex IVList of Major IPCC ReportsC
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Index573
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Indexresilience building, 378touris
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IndexEM-DAT database, 364Emissions
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Indextransformation and, 324See als
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IndexRisk sharing, 10-11, 397, 523i
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