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David Changnon
,
Stanley A. Changnon
, and
Suzy S. Changnon

Abstract

The insurance industry, insurance regulatory bodies, and scientists investigating climate change all desire long records of hail losses. Existing loss records for some states cover the 1948–present period; this span is helpful but is not long enough to define trends, possible fluctuations, and extremes adequately. The only other hail data with much longer records are the frequencies of hail days collected at National Weather Service stations since 1901, and a newly developed database for the major hail-loss states that contains hail-day data for 910 cooperative stations for 1901–94. This study tested two methods for estimating the historical loss values using hail-day data; one method produced modified hail-day values found to relate closely to loss values in the nation’s 21 primary hail-loss states. The method involved modifying a station’s hail-day values for each of the crop-season months using insurance-derived monthly hail intensity indices, resulting in an annual hail-intensity-weighted value. These weighted values of each year were combined using all stations in the crop regions of a state. The state-weighted annual indices were compared with the insurance loss values and yielded correlation coefficients of +0.60 or higher in 18 of 21 states; the resulting regression equations were used to estimate the loss values for the 1901–47 period. The temporal fluctuations and trends in the state hail intensity and loss values for 1901–94 showed major regional differences. States in the High Plains had increasing losses and greater variability with time, whereas states near the Great Lakes exhibited decreasing hail losses and variability with time. The approach can also be used to estimate loss values for areas for which historical loss values do not exist.

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J. Dettwiller
and
S. A. Changnon Jr.

Abstract

The seasonal maximum daily rainfall values for the 1871–1970 period at these three large cities in different climates were studied to discern trends. Upward trends of 19–38% were found in the warm season values at all cities, but no significant up or down trends were found in the cold season values. The upward trends in the warm season appear to reflect both natural climatic changes and inadvertent urban effects on local convective precipitation.

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F. A. Huff
and
S. A. Changnon Jr.

Abstract

On 16–17 August 1959, a severe rainstorm in which amounts exceeded 10 inches in 16 hours occurred in southern Illinois and bordering states. A dense raingage network was located on the major axis of this storm, and one of the heaviest rainfall centers along the axis was enclosed by the network. This network provided data on storm characteristics rarely available in such storms. Rainfall amounts in the network storm center exceeded the 100-year frequencies in this area. A study of this storm has been made utilizing the dense raingage network data, synoptic weather data, radar observations, U.S. Weather Bureau rainfall data, and 200 field survey measurements of rainfall. A statistical model of severe rainstorms is derived and information on the life cycle is presented.

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F. A. Huff
and
S. A. Changnon Jr.

Abstract

An investigation was made of urban effects on precipitation in and downwind of St. Louis through use of long-term climatic records within a radius of 50–75 mi of the city. Based upon radar climatological studies, two potential urban effect areas and two no-effect (control) areas were designated. Analyses were then performed to assess the urban effect on 1) total monthly and seasonal precipitation; 2) the frequency and intensity of daily precipitation; 3) the frequency of thunderstorms, hailstorms, and severe rainstorms; 4) wet-dry period rainfall; and 5) weekday-weekend precipitation (indicator of industrial-induced effect). Evidence of urban effects was found in all seasons, but appear to he strongest in late spring and summer. Results indicated an urban-induced increase in average summer rainfall ranging from 6 to 15% for distances up to 25 mi downwind of the city. The urban-increase mechanism apparently is most active on days of moderate to heavy intensifies in the natural rainfall. The urban effect was most pronounced in relatively wet summers, and indications of a suppression effect were found in dry summers. Evidence was found of an urban-induced increase in thunderstorm days within the city and of hail-day maxima downwind of the city. Overall, results appear to support thermal effects as the most important causative factor for urban modification of the natural precipitation distribution.

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F. A. Huff
and
S. A. Changnon Jr.

Abstract

An investigation was made of the potential effects of modifying growing-season rainfall on the yields and economic benefits of the two major Illinois crops, corn and soybeans. Crop yield and weather data for the 38-year period, 1931–68, were used to develop multiple regression equations relating crop yield to technology trends and various temperature and precipitation parameters. This was done for each of 13 regions with similar yield characteristics. Hypothetical seeding models were then used with the appropriate regional equation to evaluate the effects of seeding-induced changes in July-August rainfall on crop yields. Frequency distributions were developed to define expected gains or losses from seeding with each hypothetical model under assumed seeding operations lasting 1, 2, 3 and 5 years. Results indicated that in most regions of Illinois, corn and soybean crops would be benefited in the majority of the growing seasons through a cloud seeding program. Reaction to the potential seeding was found to vary substantially between regions with the same seeding model. Furthermore, seeding effectiveness may vary considerably from year to year with the same model in the same region due to the temporal variability in daily rainfall distribution characteristics.

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F. A. Huff
and
S. A. Changnon Jr.

Historical weather records at eight American urban areas of varying size, type, and climate were studied for indications of inadvertent precipitation modification. The six largest cities all had experienced warm seasonal rainfall increases of 9 to 17% during the 1955–70 period. The increases in the Midwest cities occurred largely with cold frontal systems, but in the coastal cities they were largely during air mass (non-frontal) conditions. The Midwest increases also were found to occur as enhancement, not initiation, of moderate to heavy rain days. Significant increases in summer thunder-day frequencies (13 to 41%) and hail-day frequencies (90 to 450%) were found at the six largest cities, and the increases occurred largely in the morning hours. The typical locations of maxima in the Midwest cities were thunder over and near the city, and rain and hail 25 to 55 km downwind. The maxima of all events in coastal cities were in or near the city. Overall, the results suggest that urban precipitation enhancement is related to city size, industrial nuclei generation, and urban thermal effects. The alterations have considerable relevance to urban design, local area forecasting, local water supplies, agricultural production, hydrologic design, and to planned weather modification.

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S. T. Sonka
,
S.A. Changnon Jr.
, and
S. L. Hofing

The paper presents an analysis of climate prediction needs and uses within six important subsegments of the agribusiness sector. Results are based on a mail survey of 114 managers. Although nearly 70% of the respondents indicated some use of climate predictions in the last year, only 1 in 8 of the respondents used that information in a specific decision. Lack of sufficient accuracy and prediction lead time were identified as two important impediments to current use of climate predictions. Estimates of necessary accuracy levels and lead time are reported both for the group average and by segments of need. Recommendations are offered regarding research needs to enhance climate prediction and activities of the government and the private sector to improve use of climate predictions.

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S. A. Changnon Jr.
,
R. G. Semonin
, and
F. A. Huff

Abstract

METROMEX was the first major field program aimed at studying the reality and causes of urban rainfall anomalies suggested in several climatological studies. The results from the 1971–74 METROMEX data portray statistically significant increases in summer rainfall, heavy (>2.5 cm) rainstorms, thunderstorms and hail in and just east (downstorm) of St. Louis. Examination of the rainfall yield of individual showers (cells), the spatial distribution of echo (rain) developments, and areal distribution of afternoon rain clearly point to the urban-industrial complex as the site for the favored initiation of the rain process under certain conditions. The greater frequency of rain initiations over the urban and industrial areas appear to be tied to three urban-related factors including thermodynamic effects leading to more clouds and greater incloud instability, mechanical and thermodynamic effects that produce confluence zones where clouds initiate, and enhancement of the coalescence process due to giant nuclei. Case studies reveal that once additional cells are produced, nature, coupled with the increased likelihood for merger with more storms per unit area, takes over and produces heavier rainfalls. Hence, the city is a focal point for both rain initiation and rain enhancement under conditions when rain is likely.

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S. A. Changnon
,
F. A. Huff
, and
C. F. Hsu

Use of weather modification by farm groups, state agencies, and power companies to perform operational projects continues to expand. Seven percent of the United States experienced cloud seeding during 1977. The major stakeholders—those paying, those performing the seeding, and the scientific community—have all converged on the need to evaluate operational projects. Major assessments of the national situation have recommended that carefully conducted operational projects can be a source of useful scientific information if designed, operated, and evaluated properly. A project has been launched to develop statistical-physical evaluation techniques for operational projects.

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R. I. Sax
,
S. A. Changnon
,
L. O. Grant
,
W. F. Hitschfeld
,
P. V. Hobbs
,
A. M. Kahan
, and
J. Simpson

Abstract

No abstract available.

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