IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Chapter 4Changes in Impacts of Climate Extremes: Human Systems and Ecosystemsalso credited with contributing to the lower mortality (Palecki et al.,2001).While heat waves are projected to increase in intensity and duration(Table 3-3), their net effect on human health is uncertain, largely becauseof uncertainties about the structure of cities in the future, adaptationmeasures, and access to cooling (Ebi and Meehl, 2007). Many citieshave installed heat watch warning systems. Several studies show thatthe sensitivity of the population of large US cities to extreme heatevents has been declining over time (e.g., Davis et al., 2003; Kalksteinet al., 2011).Heat waves have other effects. There is increased likelihood of disruptionof electricity supplies during heat waves (Wilbanks et al., 2008). Airquality can be reduced, particularly if stagnant high-pressure systemsincrease in frequency and intensity (Wang and Angell, 1999).Additionally, extreme heat can reduce yields of grain crops such as cornand increase stress on livestock (Karl et al., 2009).4.4.6.3. Drought and WildfireThere is medium confidence in an overall slight decrease in drynesssince 1950 across the continent, with regional variability (Table 3-2).For some regions of North America, there is medium confidence inprojections of increasing dryness (Table 3-3).Droughts are currently the third most costly category of natural disasterin the United States (Carter et al., 2008). The effects of drought includereduced water quantity and quality, lower streamflows, decreased cropproduction, ecosystem shifts, and increased wildfire risk. The severity ofimpacts of drought is related to the exposure and vulnerability ofaffected regions.From 2000 to 2010, excluding 2003, crop losses accounted for nearly alldirect damages resulting from US droughts (NWS, 2011). Similarly,drought has had regular recurring impacts on agricultural activities inNorthern Mexico (Endfield and Tejedo, 2006). In addition to impacts oncrops and pastures, droughts have been identified as causes of regionalscaleecosystem shifts throughout southwestern North America (Allenand Breshears, 1998; Breshears et al., 2005; Rehfeldt et al., 2006).Drought also has multiple indirect impacts in North America, althoughthey are more difficult to quantify. Droughts pose a risk to NorthAmerican power supplies due to associated reliance on sufficient watersupplies for hydropower generation and cooling of nuclear, coal, andnatural gas generation facilities (Goldstein, 2003; Wilbanks et al., 2008).Studies of water availability in heavily contested reservoir systems suchas the Colorado River Basin indicate that climate change is projected toreduce states’ abilities to meet existing agreements (Christensen et al.,2004). The effects of climate change on the reliability of the watersupply have been thoroughly explored by Barnett and Pierce (2008,2009).Additionally, droughts and dry conditions more generally have beenlinked to increases in wildfire activity in North America. Westerling et al.(2006) found that wildfire activity in the western United States increasedsubstantially in the late 20th century and that the increase is caused byhigher temperatures and earlier snowmelt. Similarly, increases in wildfireactivity in Alaska from 1950 to 2003 have been linked to increasedtemperatures (Karl et al., 2009). Anthropogenic warming was identifiedas a contributor to increases in Canadian wildfires (Gillett et al., 2004).In Canada, forest fires are responsible for one-third of all particulateemissions, leading to heightened incidence of respiratory and cardiacillnesses as well as mortality (Rittmaster et al., 2006). Wildfires not onlycause direct mortality, but the air pollution produces increases in eyeand respiratory illnesses (Ebi et al., 2008). The principal economic costsof wildfires include timber losses, property destruction, fire suppression,and reductions in the tourism sector (Butry et al., 2001; Morton et al., 2003).4.4.6.4. Inland FloodingThere has been a likely increase in heavy precipitation in many areas ofNorth America since 1950 (Table 3-2), with projections suggestingfurther increases in heavy precipitation in some regions (Table 3-3).Flooding and heavy precipitation events have a variety of significantdirect and indirect human health impacts (Ebi et al., 2008). Heavyprecipitation events are strongly correlated with the outbreak ofwaterborne illnesses in the United States – 51% of waterborne diseaseoutbreaks were preceded by precipitation events in the top decile(Curriero et al., 2001). In addition, heavy precipitation events have beenlinked to North American outbreaks of vector-borne diseases such asHantavirus and plague (Engelthaler et al., 1999; Parmenter et al., 1999;Hjelle and Glass, 2000).Beyond direct destruction of property, flooding has important negativeimpacts on a variety of economic sectors including transportation andagriculture. Heavy precipitation and field flooding in agricultural systemsdelays spring planting, increases soil compaction, and causes crop lossesthrough anoxia and root diseases; variation in precipitation is responsiblefor the majority of the crop losses (Mendelsohn, 2007). In 1993, heavyprecipitation flooded 8.2 million acres (~3.3 million ha) of AmericanMidwest soybean and corn fields, leading to a 50% decrease in corn yieldsin Iowa, Minnesota, and Missouri, and a 20 to 30% decrease in Illinois,Indiana, and Wisconsin (Changnon, 1996). Furthermore, flood impactsinclude temporary damage or permanent destruction of infrastructurefor most modes of transportation (Zimmerman and Faris, 2010). Forexample, heavy precipitation events are a very costly weather conditionfacing US rail transportation (Changnon, 2006).4.4.6.5. Coastal Storms and FloodingGlobal observed and projected changes in coastal storms and floodingare complex. Since 1950, there has been a likely increase in extreme sea259