This section documents how extreme meteorological events such as polar outbreaks can affect human activities. Statistics on coffee and orange production are used as qualitative indicators of long-term climate variability in the region, as related to interhemispheric indicators of polar outbreaks in present-day climates.
3.4.1. Chronology and Impacts of Polar Outbreaks in Coffee-Growing Regions of South America Since the Late Eighteenth Century
Coffee was introduced to Brazil from French Guiana at the beginning of the eighteenth century. The first seeds, planted in Cayenne in 1718, can be traced back to seedlings offered by the Dutch to the French from the Botanic Gardens of Amsterdam. Brazil is the world's largest coffee producer, supplying approximately 27% of the coffee consumed worldwide. It competes with Colombia as the world's largest exporter, ranking either first or second each year depending upon the volume of its output. It is also the second world consumer of coffee after the United States.
Historically, weather has played a major role in determining the world supply of coffee. For example, production increases after recovery from the 1953 Brazilian frost created big price declines. In another situation, drought is reported to have aggravated the effect of the July 1981 frost because it came after the crop damage had occurred. In many other frost incidents, subsequent abundant rain has helped damaged trees to recover very swiftly.
Freezing temperatures and frost affect a large part of the harvest of wheat, coffee, soybeans, and oranges in
the agricultural lands of southeastern Brazil. For southeastern Brazil, reports issued by the United States Department of Agriculture (USDA) indicated that the freeze of July 1975 (perhaps the most intense in this century) reduced the 1976-77 harvest to 9.3 million bags (60 kg/bag), compared to the 1961-80 average of 19 million bags. The damage was severe enough to motivate the moving of some coffee plantations from the former growing region of Paraná (southern Brazil) to the northern states of Sâo Paulo and Minas Gerais. This severe event is comparable to the intense freezes of August 1908 and June 1918. In 1975, some 75% of the trees in Brazil were affected in some degree, and the 1976 crop was a paltry 6 million bags.
Frost in mid-July claimed 60-70% of Sâo Paulo's 1975 -76 coffee crop and 5-10% of its sugarcane crop. The intense cold also hurt pastures, tomatoes, wheat, and bananas in that state. Because of the frost damage, virtually no coffee was harvested in the year following the freezes in Paraná, and only 25-33% of its normal harvest was projected for 1977-78.
Frigid air surged through Brazil's coffee regions during the third week of July 1981, killing buds and potentially causing a significant reduction in 1982-83 production (Haddock et al., 1981). The damage was not as severe as in 1975 when coffee trees were killed. Likewise, the Brazilian frosts in June and July 1994 caused a sharp drop in coffee production and dramatic increases in coffee prices (Marengo et al., 1997a).
Statistics on coffee production in the southern states of Brazil, available since the late 1800s, can be used to indirectly assess the presence and intensity of regional cold waves. Figure 9 shows coffee production in southern and southeastern Brazil, provided by the Brazilian Institute of Coffee and The New York Times, from 18921995. A steady increase is observed in production due to increases in the cultivated area. Large drops in production were observed after the freezes of June 1928, July 1975, June 1981, and June and July 1994, related largely to the cold weather. Estimates of losses in 1995 due to the frosts of June and July 1994 are 50-80% in the states of Sao Paulo and Paraná (Marengo et al., 1997a). For the 1995-96 production, estimates put the crop at 13.15 million bags. Marengo et al. (1997a) indicate that heavy commodity market speculation after the 24 June 1994 cold event resulted in coffee price increases of almost 70% over a few days, with the New York, London, and Chicago Stock Exchanges reacting more quickly than the Brazilian market. For 1997-98, in Brazil, mild winter weather linked to El Niño kept the top production areas free of frost, but heavier than normal rainfall in June affected the quality of the harvested crop. El Niño-induced drought in Espírito Santo failed to damage the Brazilian coffee harvest, which increased in 1997-98 to 18.86 million bags. Recently, during 16-17 April 1999, the first cold wave entered from higher latitudes and extended over central Brazil and western Amazonia. On the coffee-growing areas of southern and southeastern Brazil (western Paraná and Sao Paulo), air temperatures dropped to between 0° and 2°C, creating moderate and weak freezes. However, given the occurrence of these freezes during early stages, damage to the coffee plantations was not as severe as one would expect.
Table 1 shows a chronology of events and their intensities since 1892 for the coffee-growing areas of the state of Sao Paulo (southeastern Brazil); the most devastating events are marked as very intense. The listed frosts in coffee regions of Brazil indicate that the change over the years in temperature range is probably very small, but it takes only marginal variation and a few hours of frost one night to do real damage; as in 1975, the trees can take 2 or 3 years to recuperate. In 106 years, from 1890-1996, 18 intense freeze events brought damage to coffee production. Of these, five were considered catastrophic. On average, there has been one severe event every 6 years and one very severe event every 26 years in the coffee-growing region. Two very severe events were registered in 1892-1925 (in 1902 and 1918) and the other three in 1962-96 (in 1975, 1981, and 1994).
3.4.2. North and Central American Polar
Outbreaks and Their Impacts on the Citrus
Climate has played an important role in the development of Florida's citrus industry. Florida's subtropical climate characteristics set the stage for that state to become a major producer of oranges since the eighteenth century, ultimately becoming the world's first major producer of frozen concentrated orange juice. Freeze damage to Florida's citrus industry due to intense polar outbreaks occurring since 1977 has been responsible for launching the Brazilian citrus industry into its current position as the world's leading producer and exporter of orange juice concentrate (Miller and Glantz, 1988). Studies by Rogers and Rohli (1991), Miller and Downton (1993), Rohli and Rogers (1993), and Downton and Miller (1993) describe an increase in freeze frequencies in central Florida since 1977, which have brought about a large dislocation in the Florida citrus industry, similar to the dislocation of the coffee plantations to the north of their normal places after the freeze of July 1975 in southeastern Brazil. Citrus is also grown in the Rio Grande valley region of extreme southern Texas. As in Florida, however, production in Texas has been hampered by freezes, especially those of 1949, 1951, and 1962 (Rohli and Rogers, 1993).
Descriptions of damage to the citrus crop typically focus on freezing of the citrus, defoliation of the trees, reductions in citrus production, and damage to tree limbs or bark leading to injury or death. The most dam aging are advective freezes, wherein a powerful polar anticyclone migrates to Texas (Figs. 4C, 8A), and the winds around the eastern edge of the high often reach 50 km/hr, causing excessive defoliation and transpiration and breakage of twigs and branches, in addition to bringing subfreezing air. Damage becomes very severe if temperatures remain below — 5.5°C for more than 1 hr. The worst advective freezes were those of 1962, 1983, 1985, and 1989, in addition to those during 1835, 1894, 1895, and 1899 (discussed in more detail later). The advective freeze is that identified in the conceptual model (Section 3.3.2 and Figs. 4A-4C) and in the anticyclone tracks of Fig. 8A. Radiative freezes occur when the anticyclone at the core of the polar air mass begins to settle over the southeastern United States and Florida (Fig. 8B). Radiative cooling in the clear winter night brings air temperatures to below freezing, with the air temperature dropping to the most dangerous levels only near sunrise, after which warming rapidly occurs. While most Florida freezes may combine elements of both the advective and radiative varieties, the less damaging events have lower wind speeds and are primarily radiative.
As was pointed out in Section 3.3.2, a devastating cluster of freezes affected a large portion of Florida citrus-growing areas in January 1977, 1981, and 1982; December 1983; and January 1985 (Table 2). Florida's citrus industry survived the first three freezes without major problems. However, the advective freezes of 1983 and 1985 occurred back-to-back in adjacent winters and sent the industry into a tailspin with serious crop and tree damage. Nearly one-third of the state's commercial citrus trees were lost. The next severe freeze, in December 1989, killed a large number of newly planted tress in areas that already had been affected by the earlier events. By 1989, citrus production in northern Florida had largely been abandoned. Citrus production in northern Florida had originally been encouraged by the relatively mild winters of that region prior to 1977. The industry had suffered only relatively minor setbacks occurring about once a decade, interspersed with some rare but substantial disasters, such as the freezes of 1917 and 1962, for the first three-quarters of the twentieth century.
Figure 10 shows Florida's orange production in thousands of 90-lb boxes since 1965, as shown by Miller and Glantz (1988), and updated to 1997-98. A general rising trend can be seen over the 1970s, but in general it is clear that freezes have had very uneven effects on Florida's orange growers. Major freeze events are noted in Figs. 9 and 10, denoted by arrows. As with coffee production in Fig. 9, the effect of the cold weather is often more pronounced in the year following the freeze. Tree damage is longer lasting, while the fruit frozen on the
tree can often be salvaged, and those freezes occurring in January do not affect the harvest of early-bearing varieties. The dramatic impacts of the December 1983, January 1985, and December 1989 freezes can readily be seen. Miller and Glantz indicate that the December 1962 freeze had a striking effect on orange prices, as did that of 1977. The January 1981 and January 1982 freezes, however, had virtually no effect on prices. By the 198485 season, continued reductions in Florida production had succeeded in raising the price of Florida oranges to its highest levels in 20 years.
Northern Florida was abandoned as a citrus-growing region once before, during an earlier cluster of freezes that culminated in the nineteenth century, from 1880-1899. During this spell, the most lethal events were two severe freezes that occurred within ca. 8 weeks of each other during the 1894-95 winter. These freezes were preceded by a freeze in 1886, widely considered the worst since 1835 (see Rogers and Rohli, 1991). The 1894-95 pair of freezes was followed by the extraordinarily severe freeze of 1899 (associated with the famous East Coast blizzard described earlier), which killed both old and new citrus trees in the northern half of Florida. The late nineteenth-century freezes kept Florida citrus production below 1894 levels until 1909-10 and, as with the recent cluster, contributed to a net southward migration in the citrus production belt (Chen and Gerber, 1985).
The milder decades between the severe citrus freeze clusters appear to have been associated with a gradual northward migration in citrus production (Miller and Glantz, 1988). During these mild periods the severe freezes were sporadic (e.g., those of 1835, 1917, and 1962), and other freezes that occurred were relatively benign radiative events. The December 1962 freeze was described as the "worst since 1899" (Rogers and Rohli, 1991). Very strong cold waves occurred in 1835 and 1857 (Pardue, 1946). Since the beginning of systematic weather observations, severe cold waves have been experienced in January 1866, December 1894, February 1895, 12-13 February 1899, 2-6 February 1917, 3-4 January 1928, 12-13 December 1934, 25-29 January and 16-17 November 1940, 2 March 1941, and 15-16 February 1943. Similarly, in the nineteenth century, the 1880 freeze was the coldest since 1857, but the far more severe freeze of 1886 at the start of the nineteenth century cluster is compared to the event of 1835, which is among the worst known. The data suggest that at least half a century of comparatively milder winters precedes each severe cold-wave cluster.
Tropical fruits had also been uninjured in more than half a century at St. Augustine, FL, at the time of the freeze of 1835 (Blodget, 1857). The Autobiography of Thomas Douglas (published in 1856; Chen and Gerber, 1985) indicates that many of the trees destroyed in 1835 around St. Augustine were nearly 100 years old. Aclus-ter of severe winters over the eastern and southeastern United States is also known to have occurred during the last quarter of the eighteenth century, including the winters of 1776-77, 1779-80, 1783-84, during the United States Revolutionary War, and 1786-87, 1796-97, and 1798-99 (Blodget, 1857; Ludlam, 1966). If the St. Augustine, FL, reports are characteristic, however, either any cold waves during these winters may not have greatly affected Florida citrus production or the citrus trees may have been able to withstand them due to their age, the timing of the freeze, or other factors such as abundant soil moisture. It is interesting to note that many of the worst winter freezes in the southeastern United States have been clustered in the final quarter of each of the recent three centuries.
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