A Statistical–Meteorological Evaluation of Two Operational Seeding Projects

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  • 1 Illinois State Water Survey, Champaign IL 61820
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Abstract

As part of research concerned with operational seeding and evaluation techniques, analyses were made of two warm-season seeding projects involving rainfall enhancement: a 5-year (1975–79) aircraft seeding program conducted in 15 southwestern Kansas counties, and a ground generator seeding project conducted in 3 counties of northwestern Oklahoma in 1972–76. Data for 153 and 111 seeding days in Kansas and Oklahoma, respectively, were used. Rainfall data were obtained from the climatic raingage network of the National Weather Service. Seeding-day data were gratified according to meteorological parameters, including synoptic storm type, storm motion, and plume movement derived from the low-level wind field. Comparisons of 24-hour rainfall amounts in target and control areas were made. Movable controls determined from storm motions obtained from hourly radar data and upper-level winds were used to minimize control contamination by the seeding agent. In the southwestern Kansas operation, results indicated a target increase of 9% in the warm season rainfall, but this modest increase does not provide firm support for seeding enhancement considering rainfall natural variability, rainfall sampling deficiences, and other sources of sampling error. In the Oklahoma project, no substantial support was established for seeding-induced rainfall from the ground generator operations.

Abstract

As part of research concerned with operational seeding and evaluation techniques, analyses were made of two warm-season seeding projects involving rainfall enhancement: a 5-year (1975–79) aircraft seeding program conducted in 15 southwestern Kansas counties, and a ground generator seeding project conducted in 3 counties of northwestern Oklahoma in 1972–76. Data for 153 and 111 seeding days in Kansas and Oklahoma, respectively, were used. Rainfall data were obtained from the climatic raingage network of the National Weather Service. Seeding-day data were gratified according to meteorological parameters, including synoptic storm type, storm motion, and plume movement derived from the low-level wind field. Comparisons of 24-hour rainfall amounts in target and control areas were made. Movable controls determined from storm motions obtained from hourly radar data and upper-level winds were used to minimize control contamination by the seeding agent. In the southwestern Kansas operation, results indicated a target increase of 9% in the warm season rainfall, but this modest increase does not provide firm support for seeding enhancement considering rainfall natural variability, rainfall sampling deficiences, and other sources of sampling error. In the Oklahoma project, no substantial support was established for seeding-induced rainfall from the ground generator operations.

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