WMOD00265 - Laserfiche WebLink

Home Browse Search

EV ALUA TION OF OPERATIONAL CLOUD SEEDING IN WESTERN KANSAS 1. INTRODUcnON, SUMMARY, AND CONCLUSIONS In 1975, agricultural interests in southwestem Kansas organized a weather modification program to seed summer clouds for the purposes of increasing rainfall and suppressing crop-hail damage. The project has continued each year since then, although the project area has varied as individual counties elected to participate or not to participate on a yearly basis (figure 1.1). For its first few years, the project was called the "Muddy Road" Project. More recently it has been called the Western Kansas Weather Modification Project. Administrative support for the project is provided by the Western Kansas Groundwater Management District No.1, headquartered in Scott City, Kansas. The project has been conducted each year during the growing season, which extends from late April to September. The actual starting and stopping dates vary from year to year. Seeding is carried out each year by several aircraft equipped with one or more types of seeding devices. The silver iodide generators used have included both liquid-fueled generators burning solutions of silver iodide in acetone and solid (pyrotechnic) generators. Most of the seeding has been conducted in updrafts below the bases of convective clouds. During some years, high performance aircraft capable of cloud-top seeding have been available. The high performance aircraft are equipped with racks for droppable pyrotechnics, dry ice dispensers, or both. Additional information on seeding operations is provided in section 2. The project has operated on the assumption that additional ice particles produced in the clouds by the seeding agents would grow into snowflakes, graupel particles (sometimes called snow pellets), or small hail, and then melt to raindrops during their fall to the ground. It was reasoned that this process would tend to increase summer rainfall and would also, by increasing the numbers of frozen precipitation particles, tend to reduce their sizes and thereby decrease the probability of any of them reaching the ground as hailstones before completely melting to raindrops (the competing embryo concept of hail suppression). Since 1975, the operators of the project have recognized the importance of evaluating the effects of their operations. Some generally inconclusive analyses of the rainfall data have been published by scientists of the DJinois State Water Survey (Hsu and Chen [1] and Huff et al. [2]). In 1985, the Kansas Water Board asked the Bureau of Reclamation's Southwest Regional Office in Amarillo, Texas, for assistance in evaluating the project. The Southwest Region in turn requested the Bureau's Engineering and ReseaICh Center in Denver, Colorado, to conduct the evaluation. Work got underway in the DARR (Division of Atmospheric Resources Research) in the fall of 1985 under a plan calling for the evaluation to extend through September 1987. This report summarizes the evaluation and sets forth the conclusions reached. .. The basic approach followed was to acquim rainfall and hail data for the target area and a large surrounding study area and then examine these data for changes that could be attributed to the project activities. In addition, copies of logs of seeding activities were obtained from the Western Kansas Groundwater Managemem District No. 1 so that information about the location and amount of seeding could be compared with the rain and hail data. Details are provided in later sections of this report. <> Daily rainfall data were obtained from the National Climatic Center in Asheville, North Carolina. C.rop-hailloss data were obtained from the Crop-Hail Insurance Actuarial Association of Chicago,