A Perspective on El Niño for the Property Insurance Industry: Causes, Characteristics, Economic Impacts, and Implications

 by

 Brian D. Skinner, Peter J. Lamb, Michael B. Richman, and John T. Snow

Prepared for the Institute for Business & Home Safety

Executive Summary

The term El Niño has come to represent the occasional large-scale warming of much of the central and eastern tropical Pacific Ocean. This warming affects the position of heavy rainfall and thunderstorms in the Pacific, which in turn leads to a shift in the position of mid-latitude jet stream winds that direct the movement of weather systems. Thus, El Niño events in the Pacific Ocean lead to short-term climate changes in distant areas of the globe, including North America.

The current El Niño event began in March–April 1997 and has evolved into one of the most intense events of this century. It is predicted by certain computer models to maintain its present intensity through at least early 1998, when warm sea surface temperature (SST) anomalies are currently forecast to gradually erode. The magnitude of SST anomalies during the present event and the 1982-83 El Niño are similar. However, there are notable differences in the seasonal timing and geographical patterns of ocean warming between the two events. It has been shown that these particular characteristics of individual El Niño events strongly determine the resulting weather patterns and their societal impacts.

Possible impacts of the current El Niño on the property insurance industry over the next twelve months include the following:  

• Hurricane activity in the Atlantic typically decreases during El Niño events. In the northeast Pacific it usually produces increases in system intensity, but not in number. Both regions are most affected by El Niño conditions in the May through November time period, and therefore some continued effects may be felt through November 1997. The current event is now projected to weaken by May 1998, and little hurricane influence is projected for the 1998 season.
• Potential for flooding rains is increased in the southwestern and southeastern U.S. from November through March, and in the Southern and Central Plains during December through March. Above-normal precipitation is also expected for early next year in southeastern South America, southern India and Sri Lanka, the western South American coast, and Equatorial East Africa.
• In the U.S., the above-normal winter and spring precipitation expected for the Southwest would decrease fire danger in the summer and fall of 1998. Conversely, dry conditions are expected this winter in the northern Rocky Mountains, which would increase fire danger the following season. Elsewhere, potential for wildfires is expected to be much higher than normal in Australia and Indonesia through the coming Southern Hemisphere summer. Drought conditions may also be experienced in northeastern South America, Central America, and southeastern Africa through March–April.
• Secondary impacts around the world could include serious effects on agricultural and fishing industries, due to drought or flood conditions and warm sea waters. Marine ecosystems are likely to be significantly altered. River transport systems and other infrastructure may be affected or damaged.

The effects of El Niño on winter storms/nor’easters, severe weather occurrence, tornadoes, and hail in the U.S. have not yet been adequately addressed in the scientific community to yield predictions concerning their occurrence.

Improvements in the detection, monitoring, and prediction of the formation and evolution of El Niño events using satellite remote sensing, sea surface and upper ocean observation networks, statistical analysis, and advanced computer models now allows for the development of mitigation strategies to reduce the emotional and financial impact of these events. The insurance industry-sponsored Institute for Business & Home Safety (IBHS) and its public- and private-sector partners can use information about the possible effects of El Niño-related weather patterns to educate people about the need for advanced preparations. In the United States, where flooding is the major potential peril from El Niño, the most effective mitigation step could be for homeowners and small-business owners to purchase federal flood insurance from the National Flood Insurance Program.

Description of the Pacific El Niño Phenomenon

Originally, the term El Niño was used by fishermen along the western coast of equatorial South America in reference to the slight warming of coastal waters that occur there around the end of most years (hence, El Niño, or the "Christ Child"). However, since about 1975, this term has come to represent the occasional larger-scale warming of the waters across much of the eastern and central tropical Pacific Ocean. Events of this type have tended to occur at somewhere between two to seven year intervals, and last for 12–18 months, most often beginning in March or April. The warming of the tropical waters, now reported in terms of sea surface temperature (SST) anomalies from the climatological normal, occurs in response to a decrease in the easterly trade winds that are always present. These easterly trade winds are ordinarily sufficiently strong to induce ocean currents and upwelling that produce cold water along the equator and the western coast of South America (Figure 1). During average El Niño events, the weakened easterly winds cause the areas of colder SSTs to become warmer by 1–2^oC (1.8–3.6^oF). However, in more intense El Niño events, the warm anomalies can reach 3–5^oC (5.4–9.0^oF).

In the tropical Pacific, the location of rainfall and thunderstorms tends to closely follow the location of the warmest SSTs. As illustrated in Figure 1, during an El Niño event the warmest waters occur farther east than usual. As a result, the location of the heaviest rainfall also shifts from its normal position near northern Australia and Indonesia to closer to the central Pacific. These thunderstorms extend high into the atmosphere, and the change in their location disrupts the normal patterns of high-altitude jet stream winds that determine the movement of weather systems downstream (Figure 2). Weather patterns in many areas of the world are altered. However, North America is among the regions particularly affected because of its location immediately downstream from where the tropical influences originate.

Diagnosis and Prognosis of the Current El Niño Event

The present El Niño began in March–April 1997, when warm SST anomalies were first detected along the western coast of South America. By September, these warm SST anomalies had extended as far west as the International Date Line. At present, the SST anomalies have reached record high levels for this time of year, greater than 4^oC (7.2^oF) in the eastern Pacific (Figure 3b). In addition, the area of warmest SSTs has shifted eastward from its usual position and is located in the central Pacific (Figure 3a). Although an area of negative SST anomalies (cooler-than-normal waters) is located in the far western Pacific (Figure 3b), these anomalies are not related to the so-called La Niña, which instead is the inverse of El Niño in the central and eastern Pacific.

Figure 4 shows the latest monthly predictions available from the Climate Prediction Center of NOAA’s National Centers for Environmental Prediction, obtained using their coupled ocean-atmosphere numerical (i.e., computer) model. Results from this particular model indicate that the current El Niño will maintain its present intensity through January–February 1998. SST anomalies are then predicted to gradually decrease, with weakening warm anomalies remaining through May–June 1998. Forecasts for El Niño derived from other computer models have variable results. The NOAA Climate Prediction Center model maintains warm SST anomalies in the Pacific longer than other models, some of which indicate near-normal SSTs in the tropical Pacific as early as January 1998. Forecasts of the evolution of warm SST anomalies are important, as known climatological responses to El Niño occur in different seasons in different parts of the world (Table 1).

It terms of magnitude of SST anomalies, the present El Niño event is stronger than most other events this century. An exception is the notable event in 1982-83, with which the current event has been frequently compared in the media. However, individual El Niños have distinct characteristics that lead to differences in the resulting regional weather patterns and societal impacts. In particular, the seasonal timing and spatial pattern of the evolution of the warm SST anomalies varies between events, and recent studies have shown that exactly how weather patterns are affected is highly dependent on the precise location of the warmest SSTs. The 1982-83 event is generally regarded as atypical among El Niños in its seasonal timing (beginning later in the season during June–July and continuing through the following summer) and the evolution of its SST anomaly pattern (which first appeared in the central Pacific rather than along the South American coast). The present event more closely resembles the typical strong events that occurred in 1972-73, 1963, and 1957-58, when, in contrast, warm anomalies appeared along the South American coast in early spring and subsequently propagated westward across the Pacific.

Predicted Impacts of the 1997–98 El Niño

Possible impacts on the property insurance industry caused by short-term global climate changes related to the current El Niño event are summarized below. Primary impacts related to each of several meteorological phenomena are discussed, concentrating on the period from November 1997 through October 1998. These impacts are based upon statistically established relationships of regional weather patterns with El Niño. However, the presence of El Niño conditions does not guarantee that a particular weather pattern will be observed during any single event. To address this situation, we have included in Tables 2–4 information that indicates the "degree of confidence" in the individual relationships presented. In addition to primary impacts that are directly related to weather behavior, possible secondary impacts generated by El Niño conditions are also reviewed.

Hurricane activity: The strongest known relationship between El Niño occurrence and hurricanes is a marked decrease in hurricane activity and intensity over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Major hurricane landfalls in the eastern U.S. are decreased by 66% in El Niño years, and property insurance losses are less than average in about 78% of El Niño years. Conversely, over the Pacific Ocean off the western coast of Mexico, the number of intense hurricanes increases by 50% during El Niño years, and there are indications that these storms are more likely to affect the southwestern U.S. In addition, Pacific hurricanes may be more likely to affect mid-Pacific islands such as Hawaii and Tahiti. These relationships are summarized in Table 2.

As indicated in Table 1, the season when El Niño events typically affect Atlantic hurricane activity is from June through November. Thus, the beneficial effects of decreased activity in the Atlantic from the current El Niño have already been witnessed during the 1997 season, when Atlantic hurricane activity was much lower than the level predicted by analyses made before the intensity of the present El Niño event was known. The effects on Northeast Pacific hurricanes, which typically have peak activity in August and September, may also have already been felt. In the 1997 hurricane season, the remnants of three Pacific hurricanes (Ignacio, Linda, and Nora) affected the West Coast, producing high surf and some heavy rain and flooding. (It should be noted, however, that the warmer waters off the coast of Mexico this season, which have helped intensify these hurricanes, are thought to be mostly unrelated to the El Niño phenomenon.) High probabilities that the current El Niño event will have an effect on the 1998 Atlantic and Pacific hurricane seasons are contingent upon the warm SST anomalies continuing into summer and fall of next year. However, current forecasts (Figure 4) have the SSTs returning to near-normal before that time, which suggests little or no El Niño influence on hurricane activity.

Nor’easters: Meteorological research to date has not yet investigated possible connections between El Niño occurrence and the formation of intense winter storms along the East Coast. However, inferences regarding possible relationships could be made. As indicated in Figure 2, changes in the jet stream which occur during an El Niño event do increase the potential for storms to form over the southern/southeastern U.S. and in the Gulf of Mexico. These storms often propagate northeastward toward the East Coast and can sometimes develop into nor’easters. However, there is currently no information to suggest that this occurs more or less often during El Niño conditions. A preliminary examination of the dates of major East Coast snowstorms since 1900 does not reveal any preference for their formation during El Niño years. Future research is needed to closely examine the record of nor’easter occurrence and the atmospheric conditions that can lead to their formation, to determine if any relationships with El Niño conditions exist.

Floods: Potential for flooding rains in the U.S. and other parts of the world may be increased in regions where higher-than-average rainfall usually occurs in conjunction with El Niño occurrence. A number of such regions have been identified in the U.S. and the world (Figure 5), and their relationships with El Niño are summarized in Table 3. Although increased rainfall is not necessarily indicative of flood occurrence, the potential for flood occurrence is likely increased in these locations.

In the U.S., the strongest associations between increased rainfall and El Niño occurrence have been found for the Southeast/Gulf Coast (November–March), California and the Southwest (October–March), the Southern and Central Plains (March), and the Southeast/Mid-Atlantic (June). The relationship in California appears to vary from south to north and is dependent on the particular type of El Niño event. Events with characteristics similar to the present El Niño have been linked with increased precipitation more consistently in southern California than farther to the north.

Since El Niño conditions are predicted by some computer models to remain in the Pacific at least through March 1998, the possibility of wetter-than-normal conditions exists for all of the above regions of the U.S. Wet conditions are also likely to prevail in those areas of the world identified in Table 3, which includes "confidence" information about the rainfall relationships with El Niño. Flooding rains and heavy snowfall are already being observed this season in Chile and Peru.

Actual predictions from the Climate Prediction Center for monthly U.S. precipitation for November 1997–December 1998 (Figure 6) are consistent with many of the relationships documented above. Probabilities of above-normal precipitation from November through April range from 45–65% (i.e., greater than the 33% that exists by "chance") for the region from California to Texas and along the Gulf Coast into Florida. Above-normal precipitation is also predicted for the Great Plains from Texas to Nebraska from December through March.

Wildfires: Limited research has been completed that associates El Niño occurrence directly with wildfire activity, but the small number of available studies has uncovered relationships for parts of the U.S. and Australia. Where direct wildfire research is not available, the potential for increased fire activity may be determined by considering regions that are known to experience drought conditions during El Niño events. A summary of information about known and inferred wildfire and drought relationships with El Niño in certain regions of the world is given in Table 4.

The greatest association between wildfires and El Niño occurs in eastern Australia, where El Niño conditions yield a high probability that spring and summer rainfall (October–March) will be less than average, and increase the likelihood of exceeding the average number of fire-risk days. The risk may be increased if rainfall in the preceding seasons was above-normal, enhancing the growth of brush and grasses to fuel fires.

In the southwestern U.S., El Niño conditions tend to increase precipitation in the fall and winter, which may increase vegetation growth and hence potential fuel for fires. However, the increased snowpack and moisture retained in large trees and brush into the next season have a greater, and offsetting, effect. Thus, potentially flooding rains and heavy snow have the beneficial secondary impact of decreasing fire danger in the southwestern U.S. during the following summer. Conversely, in Montana and Idaho, El Niño occurrence decreases winter rainfall and snowpack, causing increased fire potential the following summer season. In the southeastern U.S. and near the Mid-Atlantic coast, El Niño leads to decreased precipitation in July and August at the beginning of the potential fire season, and in Florida, increased winter precipitation has been linked to a decrease in fire activity for January–May.

Forecasts for November 1997 through March 1998 indicate a 45–75% (relative to 33% by chance) probability of increased fall and winter precipitation in California (Figure 6), which may promote an early end to this season's fire activity, and decrease activity next summer. However, there are concerns that the predicted dry conditions in Montana, Idaho, and adjoining Canadian provinces this winter may lead to a higher fire risk next summer. Greatest concerns are in Australia, where the forecast for the spring and summer is for continued dry conditions that are expected to lead to an early onset of the period of high fire danger. Dry conditions should continue to prevail in Indonesia as well, where out-of-control forest fires and resultant haze are already making headlines, and have been implicated as a possible cause of the crash of a Garuda Indonesia airliner on September 27.

Tornadoes, severe thunderstorms, and hail: The possible relationship between El Niño conditions in the tropical Pacific and the incidence of severe weather in the U.S. has not been appropriately addressed in the meteorological literature. In general, the atmospheric processes that control the formation of severe thunderstorms capable of producing tornadoes and large hail are most immediately dominated by local-to-regional-scale conditions. However, El Niño events in the Pacific may alter the large-scale atmospheric environment and flow patterns that govern the overall potential for the development of severe storms. For example, one recently proposed relationship is that El Niño conditions lead to the southward displacement of necessary upper-level wind patterns in the Great Plains, causing a decrease in tornado occurrence. El Niño conditions may also influence the availability of moisture in the lower atmosphere, which is a crucial requirement for producing the vertical instability needed to support severe storms. Considerable future research is needed to investigate hypotheses such as these that may explain the effect of El Niño occurrence on the distribution of tornadoes, large hail, and severe thunderstorms in the U.S.

secondary impacts: In addition to the direct weather-related impacts that may lead to property insurance losses, El Niño events also generate important secondary effects on world agricultural production and related industries, environmental ecosystems, transport systems, and infrastructure. These secondary impacts can have devastating societal impacts and lead to serious disruption of world economies and markets, which may ultimately have additional financial repercussions upon the insurance industry. Agricultural and fishing industry losses, in particular, have been among the most costly secondary effects of previous El Niño events. For example, crop failure in southern Africa in 1982-83 caused widespread disease and famine and is estimated to have cost about $1 billion. A brief listing of possible secondary effects resulting from the current El Niño event is given in Table 5.

Application of Climate Information for Mitigation

In recent years, atmospheric scientists have made significant improvements in their ability to detect, monitor, and predict the formation and evolution of El Niño events, through the use of satellite remote sensing, sea surface and upper ocean observation networks, statistical analysis, and advanced computer models. As a result, individual homeowners, communities, businesses, and government agencies now have the opportunity to prepare for and mitigate possible adverse El Niño effects. Examples of such loss mitigation activities currently being undertaken in response to El Niño forecasts issued in recent months are given in Table 6.

These mitigation efforts will prove to be advantageous for all stakeholders in the long term. Although it is not possible to predict with absolute certainty whether adverse weather patterns will arise in response to a particular El Niño event, the "confidence information" provided in Tables 2–4 indicates that these weather patterns and associated damage are observed in the majority of events in most locations. Systematic application of reasonable strategies for reducing vulnerabilities in response to meteorological predictions of El Niño conditions will ultimately procure favorable benefits for everyone.

Advance preparations now being completed in California offer an excellent example of the benefits of El Niño forecasts and the opportunities for prevention. Insurance companies have released public service announcements offering guidance for homeowners about securing their properties and purchasing federal flood insurance from the National Flood Insurance Program. Communities have cleared drainage systems and reinforced seawalls, and businesses have rescheduled activities, all in an effort to reduce property damage and losses from anticipated stormy weather. In the future, simple monitoring of forecasts for El Niño will enable the Institute for Business & Home Safety (IBHS), its insurance company members, and its public- and private-sector partners to educate policy holders about the need for advance preparations in their area. In addition to these mitigation efforts, climate information concerning El Niño may also be used within the insurance industry to ensure that claims operations are ready to respond immediately to each future El Niño event.

Increased interaction between the insurance community and meteorological community is apt to uncover further uses of El Niño and climate information in the insurance industry, as atmospheric scientists gain an increased awareness of insurers’ goals and needs. Such interaction will enable individual homeowners, communities, businesses, and government agencies to continue to benefit from meteorologists’ increasing understanding of El Niño events, accompanying improved ability to anticipate their physical evolution, and increased awareness of their societal and economic impacts.

Table 1: Time period for expected occurrence of meteorological phenomena in the United States and elsewhere in the world during El Niño events.

Figure 1: Diagram illustrating the state of the tropical Pacific Ocean during normal and El Niño conditions. During El Niño events, easterly trade winds in the Pacific decrease in strength, leading to anomalies in surface ocean currents (white arrows), and causing a change in the location of the warmest sea surface temperatures (red shading) and associated thunderstorms (NOAA El Niño Theme Page, 1997).

Normal Conditions

El Niño Conditions

Figure 2: Illustration of the changes in upper-level jet stream patterns over the Pacific, which typically occur during El Niño episodes. Normal flow toward the northwestern United States is deflected northward toward the Canadian and Alaskan coasts. At the same time, a secondary southern storm track appears that increases the probability of storm systems affecting the California coast, and increases the potential for storms to form in the Gulf of Mexico (Wallace and Vogel, 1994).

Figure 3: (a) Sea surface temperature (SST) observations in the tropical Pacific as of October 1, 1997, and (b) their departure from normal conditions. The area of warmest waters ( ³ 28^oC) is shifted east of its normal location west of the International Date Line. SST anomalies along the western coast of South America have now reached record high levels for early October (Climate Prediction Center, 1997).

Figure 4: Numerical (i.e., computer) model forecasts from the Climate Prediction Center of the expected evolution of the current El Niño event, in terms of SST anomalies (^oC). El Niño conditions are forecast to maintain their current intensity through January 1998, after which a gradual decrease in the strength of warm SST anomalies is predicted through May–June 1998. Tropical Pacific SSTs are forecast to be near-normal by next summer (Climate Prediction Center, 1997).

Figure 5: Documented climate variations in various regions around the world which have been associated with the occurrence of El Niño conditions in the tropical Pacific. Further information about precipitation relationships in certain regions is included in Tables 2 and 3 (NOAA El Niño Theme Page, 1997).

Figure 6: Latest forecasts from the Climate Prediction Center of expected deviations of U.S. precipitation from normal conditions, for overlapping three-month periods from November 1997–December 1998. In unshaded regions, there is an equal probability for above-normal, normal, and below-normal conditions (33% each). Green and orange shading indicate successive increases in probabilities, at 5% intervals, for above-normal and below-normal precipitation, respectively (Climate Prediction Center, 1997).

Sources: Gray and Sheaffer 1991; Cayan and Webb 1992; Property Claims Services 1995; Atlantic Oceanographic and Meteorological Laboratory 1997; National Weather Service 1997

Table 2: Summary of known relationships of hurricane activity with El Niño occurrence and expected impacts of the current event over the next twelve months.

Sources: Schonher and Nicholson 1989; Null 1993; Allan et al. 1996; Ropelewski and Halpert 1996; Climate Prediction Center 1997; Department of Natural Resources, Queensland, Australia 1997; Montroy 1997; Montroy et al. 1997; National Drought Mitigation Center 1997

Table 3: Summary of known relationships of increased precipitation (increased flood potential) with El Niño occurrence and expected impacts of the current event over the next twelve months. Predictions for U.S. and global precipitation were obtained from the Climate Prediction Center and the Department of Natural Resources in Queensland, Australia. Indicated U.S. and global probabilities are relative to a 33% and 50% "chance" probability of experiencing above-normal precipitation, respectively.

Sources: Stern and Williams 1989; Allan 1991; Brenner 1991; Swetnam and Betancourt 1991; Ropelewski and Halpert 1996; Bureau of Meteorology, Australia 1997; Climate Prediction Center 1997; Department of Natural Resources, Queensland, Australia 1997; Montroy 1997; Montroy et al. 1997; Williams 1997

Table 4: Summary of known relationships of wildfires and drought (increased fire potential) with El Niño occurrence and expected impacts of the current event over the next twelve months. Predictions for U.S. and global precipitation were obtained from the Climate Prediction Center and the Department of Natural Resources in Queensland, Australia. Indicated U.S. and global probabilities are relative to a 33% and 50% "chance" probability of experiencing above- or below-normal precipitation, respectively.

Sources: Wallace and Vogel 1994; Epstein 1997; National Oceanic and Atmospheric Administration 1997a; Suplee 1997

 Table 5: Possible worldwide secondary impacts of the 1997-98 El Niño on agricultural industries, environmental ecosystems, and infrastructure.

Table 6: Recent activities, based on forecasts of the current El Niño, that are being undertaken to mitigate potential losses due to related adverse weather patterns. (Compiled from newspaper and magazine articles and online publications included in the bibliography.)

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