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David Changnon and Stanley A. Changnon

Abstract

Crop-hail insurance loss data for 1948–94 are useful as measures of the historical variability of damaging hail in those 26 states where most crop damages occur. However, longer records are needed for various scientific and business applications, as well as information on potential losses in United States’ areas without crop insurance. The long-term (1901 to present) data on hail-day incidences, as derived from National Weather Service historical station records, were investigated to determine if some form of a hail-day expression related well to the insurance losses. The areal extent of insured areas of Illinois, Texas, and Nebraska experiencing growing season frequencies of hail days matching or exceeding the once in 10-yr frequencies was found to have the best relationship with insured loss values. The computed correlation coefficients were +0.97 for Illinois, +0.73 for Texas, and +0.91 for Nebraska. These values appear to be a useful surrogate for 1) estimating pre-1948 loss values, 2) estimating loss values in areas with no insurance, and 3) further research involving other states with different crop and hail conditions.

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David Changnon and Stanley A. Changnon

Abstract

Uses of climate information have grown considerably in the past 15 years as a wide variety of weather-sensitive businesses sought to deal effectively with their financial losses and manage risks associated with various weather and climate conditions. Availability of both long-term quality climate data and new technologies has facilitated development of climate-related products by private-sector atmospheric scientists and decision makers. Weather derivatives, now widely used in the energy sector, allow companies to select a financially critical seasonal weather threshold, and, for a price paid to a provider, to obtain financial reparation if this threshold is exceeded. Another new product primarily used by the insurance industry is weather-risk models, which define the potential risks of severe-weather losses across a region where few historical insured loss data exist. Firms develop weather-risk models based on historical storm information combined with a target region’s societal, economic, and physical conditions. Examples of the derivatives and weather-risk models and their uses are presented. Atmospheric scientists who want to participate in the development and use of these new risk-management products will need to broaden their educational experience and develop knowledge and skills in fields such as finance, geography, economics, statistics, and information technology.

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Stanley A. Changnon and David Changnon

Abstract

Hail-day occurrences during a 100-yr period, 1896–1995, derived from carefully screened records of 66 first-order stations distributed across the United States, were assessed for temporal fluctuations and trends. Shorter-term (5- and 10-yr) fluctuations varied greatly and were often dissimilar between adjacent stations reflecting localized differences in hailstorm activity, making temporal interpretations difficult. But temporal fluctuations based on 20-yr and longer periods exhibited regional coherence reflecting the control of large-scale synoptic hail-producing systems on the point distributions over broader areas. Classification of station fluctuations based on 20-yr periods revealed five types of distributions existed across most of the nation. One present in the Midwest had a peak in hail activity in 1916–35 followed by a general decline to 1976–95. Another distribution had a midcentury peak and was found at stations in three areas: the central high plains, northern Rockies, and East Coast. The third distribution peaked during 1956–75 and was found at stations in the northern and south-central high plains. The fourth temporal distribution showed a steady increase during the 100-yr period, peaking in 1976–95, and was found in an area from the Pacific Northwest to the central Rockies and southern plains. The fifth distribution found at stations in the eastern Gulf Coast had a maximum at the beginning of the century and declined thereafter. The 100-yr linear trends defined four regions across the United States with significant up trends in the high plains, central Rockies, and southeast, but with decreasing trends elsewhere in the nation. These up trends have occurred in areas where hail damage is greatest, and the trends matched well with those defined by crop-hail insurance losses and those found in studies of thunderstorm trends. The national average based on all station hail values formed a bell-shaped 100-yr distribution with hail occurrences peaking in midcentury. Thunderstorm data from the 66 stations, also based on screening to ensure quality data, revealed a bell-shaped distribution similar to the hail-day distribution, and national hail insurance loss values have declined since the 1950s, also agreeing with the hail-day decrease since midcentury. The national distribution differs markedly from certain regional distributions illustrating the importance of using regional analysis to assess temporal fluctuations in severe weather conditions.

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Stanley A. Changnon Jr.

Abstract

The distribution of hail days during 1961–80 in the northern Great Plains-Midwest was evaluated on a temporal and spatial basis to help interpret crop-hail losses. Comparisons with earlier (1901–60) hail day data revealed the seven-state study area contained eight permanent areas of high and low incidences found in any 5-year or longer period. The high hail incidence areas were related either to major topographic features or to areas of frequent frontal occurrences. Certain other areas of high or low hail incidence appeared at random locales, lasted 5 to 20 years, and disappeared. The annual and July incidences of hail increased sporadically but steadily from 1901 to 1980 in the Dakotas, Nebraska and Minnesota, reaching a peak during 1961–80. This has led to relatively more crop damage in recent years. In Montana, eastern Iowa, and Illinois, hail has decreased to a low in 1961–80. During the 1961–80 period, hail maximized in 1961–65, being 30% more frequent than in any subsequent 5-year period.

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Stanley A. Changnon Jr.

A technology assessment of the future potential of hail suppression and all its possible ramifications in the United States in future years has included an attempt to define the current status of hail suppression. Hail suppression is at a stage in which the socioeconomic impacts of its use and the means to optimize its future utilization can be adequately treated. The estimation of a wide range of future suppression capabilities was based on the current status, which was defined after inspecting three sources of information: 1) results from preliminary evaluations of six recent projects, 2) findings on four published assessments of weather modification, and 3) results from two opinion surveys. This investigation indicates: 1) scientific beliefs about existing capabilities are widely different, with the majority of experts believing there is no capability; 2) the published reviews are optimistic but largely nondefinitive; and 3) the results of five of six recent suppression projects show suppression levels of 20–50%, but the results are largely not significant at the 5% level. This difference between average beliefs of experts and the results of recent projects suggests the need for an extensive investigation of the data and results of these recent projects.

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Stanley A. Changnon Jr.

Abstract

An understanding of applied climatology and its information-generating research requires recognition of the total cause-and-effect spectrum including the issue detection, the research effort pursued, the type of product, the users, and their applications of findings. Twenty climatic information studies done at the Illinois Climate Center in 1977-79 are reviewed to illustrate why they were done, often as a result of general inquiries or specific requests, and a few of their key results. The studies each required from weeks to months to complete. Most users of the results fell in two general classes, government or business-industry. The studies revealed applications in three areas: the design of facilities, the planning and/or operations of facilities and activities, and the climatic assessment of weather extremes.

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Stanley A. Changnon

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Climatological assessments of past fluctuations in thunderstorms and other weather extremes require high-quality records. Data on thunder-day occurrences exist at U.S. first-order stations (FOS) since 1894 and represent the only long-term data available for temporal thunderstorm assessments. A thunder day is based on hearing thunder, and hence audibility is a major factor affecting record quality. Assessment of the potential conditions that affect audibility and of other factors that influence record quality identified four factors. Changes in audibility can occur from structural changes at the station, altered levels of noise such as increased aircraft operations, and relocations of stations to sites with different audibility conditions. Another data-limiting factor is local changes in storm activity due to urban influences on the atmosphere. Station relocations in areas where sharp natural differences in storm frequency exist such as in coastal and mountainous sites are a third factor affecting local values, and uncertainties related to record keeping are the fourth. The quality of the thunder-day records at the 130 U.S. FOS with 90 or more years of data during 1896–1995 were evaluated using a five-step process. First, the historical thunder-day frequencies were compared with the station relocations to detect any major changes after site changes. Second were tests of homogeneity using data from surrounding stations. The third step involved comparison of each station’s historical fluctuations with those of surrounding stations to identify anomalous values that persisted for 20 years or more. Step four involved assessment of possible urban effects on local storm frequencies using past findings and assessments of where and when urban storm activity may have changed in relation to the locations of the local weather station. Fifth, reported thunderstorms were compared with nearby cloud-to-ground lightning strokes to assess unreported thunder occurrences. Homogeneity testing revealed that 10 FOS had questionable records resulting from major multidecadal shifts in values, often a result of station relocations. Six other stations had urban influences on local storm activity that made their records unrepresentative of regional climate conditions, and four stations had anomalously low values of storms based on comparisons with nearby lightning activity. In all, 20 of the 130 stations with long records were found to have records unsuitable for long-term climatic assessments.

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Stanley A. Changnon Jr.

Abstract

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Stanley A. Changnon

Abstract

Records of monthly sky cover, sunshine and temperature for 1901–77 in a 10-state midwestern area were analyzed on a temporal and spatial basis to discern long-term trends and indications of shifts potentially due to added cirrus generated by jet aircraft since about 1960. The skycover data show generally long-term increasing frequencies of cloudy days and decreases in clear days since 1901. Percent of possible sunshine also shows a decrease but to a lesser extent than clear day frequencies. Changes have been greatest since the 1930's. The greatest shifts to cloudier, less sunny conditions occurred since 1960 in an east-west zone across southern Iowa-northern Missouri, northern two-thirds of Illinois and Indiana, and extreme southern sections of Wisconsin and lower Michigan, the area where commercial jet traffic has been greatest. The long-term trends give evidence of natural climate changes, whereas the localized shifts to more cloudiness in the central area since 1960 suggest anomalous changes related to jet-induced cirrus. Months with moderated temperatures (below average maximum and above average minimum) have increased since 1960 in the central east-west zone and largely in summer and fall, the seasons with the major shifts to cloudiness.

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Stanley A. Changnon

The drought of 1988 rated as one of the nation's worst in the past 100 years, resulting in a myriad of impacts and responses. A notable, largely unexpected impact involved stoppages of barge traffic on the lower Mississippi River during June and July, a result of shallow areas produced by record low flows and shoaling. The barge industry hauls 45% of all bulk commodities (grains, coal, petroleum) shipped in the central United States. The low flows were a result of the unusually large areal extent of drought conditions across most of the Mississippi Basin, which comprises 40% of the continental United States. Most 1987 months had been relatively warm and dry, minimizing moisture in the soils and shallow ground water. Then deficient snowmelt (due to low winter snowfalls) and record low spring 1988 precipitation combined to produce the record low flows along much of the Mississippi River.

Most responses to the drought came in a crisis mode and included concentrated dredging to open channels, government enforced reductions in barge loads and in numbers of barges per tow, tripled barge shipping rates, and shifts in transportation modes. The barge industry suffered a 20% income loss. The total losses to the barge industry coupled with higher costs for shipping were $1 billion. The Illinois Central Railroad, which parallels the major blocked waterways, used a climate prediction to anticipate the low flows 3 months in advance. They leased additional cars to help handle the increased shipments transferred from barges and made a sizable profit. A response proposed by Illinois and shippers—a temporary increase in the water diverted from Lake Michigan to raise the levels on the lower Mississippi River—was met with strong objections by other lake states and Canada. The federal government declined the proposal, but the sizable controversy it engendered reflects the growing sensitivity to water resources issues in the Great Lakes Basin and is also illustrative of problems to be expected from a drier future climate (as hypothesized by certain global climate models as a result of ever-increasing trace gases in the atmosphere). This case study illustrates the value of using seasonal climate predictions of limited skill, and the need for better near real-time climatic data, including information about physical impacts of current climatic conditions.

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