Synopsis of DRI Cloud Seeding Program

Winter StormPurpose of the Program

Augment snowfall in mountainous regions that supply water to northern and southern Nevada, and increase the snowpack and resultant runoff from the targeted basins.

Areas of Activity

Past and current projects include the basins of Lake Tahoe, the Truckee River, the Carson River, the Walker River, the Upper Humboldt River (Ruby Mountains), the South Fork of the Owyhee River (Tuscarora Mountains), the Reese River (Toiyabe Mountains), and several areas in the Upper Colorado River Basin.

History of Operation

Cloud seeding has been conducted in the Tahoe and Ruby Mountain areas since the 1960's. The DRI has designed and operated the program since its inception. The original seeding equipment was acquired mainly through U.S. Bureau of Reclamation (USBR) grants to DRI (e.g., Pyramid Lake Project). The Ruby Mountain operational project started in 1981 using surplus USBR generators. State funding for the program began as early as 1979-80, and State funding continued through 2009. The Walker River Irrigation District (WRID) has funded additional equipment for the program in the Walker Basin. In 2007 the DRI added equipment to programs in Colorado to enhance seeding activity in the Upper Colorado River Basin. These additions were funded by Lower Basin agencies including the Southern Nevada Water Authority.

Methods of Operation

Cloud Seeding EquipmentPrimarily, ground-based generators are used to burn a solution of silver iodide, sodium iodide, salt and acetone to release microscopic silver iodide particles which can create additional ice crystals, then snow, in winter clouds. Weather conditions are selected to optimize fallout in targeted basins. Generators are remotely operated by telephone landline, by radio or by other types of wireless communication. A seeding aircraft is frequently used to augment ground seeding operations. The aircraft releases AgI from pyrotechnic flares or wing-mounted solution burners. Dry ice is also used occasionally to seed shallow cloud systems, including fog over airports.

Seeding Equipment

Twenty five (25) remotely controlled silver iodide generators designed and constructed by DRI. One experimental liquid propane seeding unit in Colorado. One subcontracted seeding aircraft.

Supporting Equipment

Weather stations on seeding generators in each targeted basin. DRI/NWS hydro-meteorological network in the Tahoe area - access to RAWS, SNOTEL and other meteorological data networks through the DRI Western Regional Climate Center - NEXRAD radar and GOES satellite imagery - the DRI trace chemistry laboratory - an NCAR ice nucleus counter for detecting AgI plumes - laser imaging probes for measuring cloud and precipitation particles.

Facility

Offices and shops in Stead, NV are used for equipment fabrication, maintenance and storage.

Supporting Personnel

Three field technicians install and maintain all generator networks and fabricate new generators - DRI faculty forecast for seeding operations, implement design changes, evaluate operations, monitor environmental aspects of the program, evaluate seeding effectiveness and complete project reports.

Estimated Benefits of Program

Checking snow depthBenefits vary with the seasonal frequency of suitable weather opportunities. Research results have documented precipitation rate increases of a few hundredths to about 2 millimeters per hour due to ground-based seeding during the proper weather conditions. Based on the rate increases, estimates of augmented snow water from the DRI seeding program have varied from 20,000 to 80,000 acre-feet annually over the past 15 years of operation. Seasonal percentage increase estimates have varied from 2% to 10%. The cost of augmented water, based on the annual cost of the program, has ranged from $7 to about $18 per acre-foot.

Cooperative DRI Research

The DRI seeding program originated as an outgrowth of DRI weather modification research programs funded through the USBR and the National Oceanic and Atmospheric Administration (NOAA). DRI has also participated in numerous cloud seeding research experiments around the world. Pertinent research findings are immediately applied to operations. Research equipment is often shared with the operational program at no additional cost. Current DRI research is aimed at quantitative evaluation of winter storm cloud seeding using 1) ultra trace chemical analysis of snow samples to verify the occurrence of the seeding material in target areas; 2) atmospheric model simulations of seeding plume transport; and 3) hydrologic modeling to estimate the additional runoff due to cloud seeding.

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