NORTHERN CHILE WINTER CLOUD SEEDING FEASIBILITY/DESIGN STUDY DON A. GRIFFITH NORTH AMERICAN WEATHER CONSULTANTS (NAWC) SANDY, UTAH WMA SEMI-ANNUAL CONFERENCE SEPTEMBER 25-27, 2013 SANTIAGO, CHILE
INTRODUCTION North American Weather Consultants (NAWC) was contacted by a mining interest in Chile asking about the feasibility of conducting a cloud seeding program in the upper Copiapo River Basin located in northern Chile. This initial contact lead to a site visit by Mr. Don Griffith (President of NAWC) to tour the potential target area and meet with local Chilean weather officials and water users. This site visit occurred in late May 2008. Based upon knowledge gained during this initial trip, NAWC submitted a proposal to conduct a detailed feasibility/design study. The mining company accepted this proposal and the work was begun in September 2008. A final report was submitted to the client in July 2009. Of Note; the American Society of Civil Engineers Guidelines for Cloud Seeding to Augment Precipitation (2006) indicates that a site specific feasibility study should be performed before a cloud seeding program is Implemented. If a program is not deemed to be feasible, then obviously a program should not be attempted.
GOAL OF STUDY The stated goal of the program is to increase winter snow pack in the target areas to provide additional spring and summer streamflow and recharge underground aquifers at a favorable benefit/cost ratio without the creation of any significant negative environmental impacts.
FEASIBILITY/DESIGN STUDY TASKS TO BE PERFORMED Review and Summary of Prior Studies and Research (Task I) Review and Analysis of Climatology of the Target Area (Task II) Development of a Preliminary Program Design (Task III) Establishment of Operational Criteria (Task IV) Development of Monitoring and Evaluation Methodology (Task V) Review of Environmental and Legal Aspects (Task VI) Development of Cost Estimates (Task VII) Final Report Preparation (Task VIII) Coordination Meetings and Presentations (Task IX)
PROPOSED TARGET AREA NAWC proposed that the target area for the project include the upper portions ( > 3000 meters) of the three tributaries to the Copiapo River: 1) Rio Jorquera 2) Rio Pulido and 3) Rio Manfla plus the area north of the Rio Jorquera within the Copiapo River basin. Average crest height of the Andes in this area is > 4000 meters.
MAP OF PROPOSED TARGET AREA
SUPERCOOLED (< 0 C) CLOUD WATER DROPLETS: THE TARGET OF WINTER CLOUD SEEDING
IDEALIZED SCHEMATIC OF THE LOCATION OF A SUPERCOOLED LIQUID WATER ZONE IN RELATION TO A MOUNTAIN BARRIER UNDER WINTER STORM CONDITIONS
STORM PERIODS NAWC identified 36 storm periods that impacted the proposed target area during the winters of 2000 to 2006. Identification of these storm periods was based upon the observation of at least 5mm of precipitation at two lower elevation precipitation observation stations. NAWC acquired the rawinsonde (weather balloon) observations from Antofagasta and Santo Domingo for these storm periods. These two locations bracket the area of interest. Normally two soundings are made per day (00 and 12Z) but the Antofagasta site only conducts one sounding per day at 12Z. NAWC averaged some information of interest for the Antofagasta and Santo Domingo 12Z soundings to give a rough idea of the storm conditions in the proposed target area.
Courtesy of World Trade Press
PRECIPITATION AMOUNTS Site elevation 1950 m Site ~ 110 km south of target elevation ~ 4500m
PHOTO of SNOW DRIFTS FOLLOWING A MAY 6, 2007 WINTER STORM THAT IMPACTED THE PROPOSED TARGET AREA (Note Barren Landscape)
700 and 500 mb Storm Period Averages of Some Parameters of Interest Height Degrees C Wind Direction Wind Speed (kts) 700-mb average 3.0 325 26 500-mb average -14.6 307 44 Note: The average height of the -5 0 C level was 4.3 km (~ 14,000 feet MSL). 700 Mb Wind Rose during Storm Periods
ATMOSPHERIC STABILITY An analysis of the Antofagasta and Santo Domingo storm upper-air soundings indicated there were frequent atmospheric stability layers or inversions below the 500mb level. For Santo Domingo, there were 27 out of 34 cases with stability layers or inversions below the average height of the 5 0 C. Similar numbers for Antofagasta were 28 out of 34 cases. The presence of atmospheric stability layers below the height of the 5 0 C means that it is unlikely that silver iodide released from ground generators would ever reach the silver iodide effective level in a significant number of the storm periods. Consequentially, the usefulness of ground based generators located below the average height of the 5 0 C level (4.3km) would be questionable. The installation of remotely controlled ground based generators near this elevation could potentially be considered although correct targeting of the effects of seeding might be difficult considering the mean wind directions during storms (northwest) versus the availability of ground sites at this elevation located northwest of the target area. It is NAWC s impression such regions would be rugged, remote areas.
EXAMPLE OF A MANUALLY OPERATED SILVER IODIDE GENERATOR
EXAMPLE OF A REMOTELY OPERATED SILVER IODIDE GENERATOR
EXAMPLES OF AIRBORNE SEEDING METHODS
AIRCRAFT EJECTABLE SILVER IODIDE FLARE RACK
POTENTIAL EFFECTS OF CLOUD SEEDING The Estimated Effects of Cloud Seeding on Precipitation in the Copiapo Drainage are Expected to fall within the 5 to 15% Range per the Weather Modification Association s Capability Statement. (September 2011)
CLOUD SEEDING PROGRAM EVALUATIONS NAWC considers the historical target/control technique to be the best choice in evaluations of non-randomized, operational wintertime cloud seeding projects if the goal of such an evaluation is to establish some quantitative estimate of the increase in precipitation, snowpack or streamflow due to seeding. The development of regression equations using the target/control technique a priori, i.e., before any seeding is conducted, offers a means of eliminating any question of bias on the part of those conducting the subsequent evaluations. This is a step that is encouraged by the Weather Modification Association; that is, procedures to be used in evaluations should be specified in advance.
r 2 Values from Correlations between Annual Water Year (May through April) Streamflow at the Rio En Las Lozas Gage (Huasco Drainage) Versus Six Different Gages along the Copiapo River, 1975-2003. Copiapo Stations Water Year Correlation (r 2 ) Rio Jorquera En Vertedero 0.80 Rio Pulido En Vertedero 0.97 Rio Manflas En Vertedero 0.93 Rio Copiapo En Lautaro 0.73 Rio Copiapo En Pastillo 0.98 Rio Copiapo En La Puerta 0.86 Generally good correlations; regression equations should be useful in estimating natural streamflow to be compared to actual streamflow during seeded years to determine if there are any systematic differences. Assumes the Huasco Drainage is not seeded in years the Copiapo Drainage is Seeded.
KEY RECOMMENDED DESIGN COMPONENTS Winter Program: April 15 to September 15 Seeding Agent: Silver Iodide (AgI) Seeding Mode: Airborne Liquid AgI and Ejectable AgI Flare Seeding (Turbine Aircraft). 24/7 Operations (Need to Maximize Seeding during Limited Opportunities). Seeding Suspensions during Potential Flash Flood Events. Provision for a Program Dedicated 5 cm Weather Radar, Located Upwind of the Target Area, Equipped with Aircraft Tracking System. Field Office Established at Radar Site with Internet, Telephone and Radio Communications. Program On Site Personnel: Experienced Cloud Seeding Meteorologist, One or Two Experienced Pilots, Part Time Technician. Program Evaluation Annual Final Report
ESTIMATED COSTS Preliminary cost estimates (in U.S. Dollars) were prepared for two winter seasons of cloud seeding based upon the recommended design provided in the report. Cost estimates were provided for a five-month operational period (April 15 through September 15). Costs estimates included reimbursable expenses of seeding (e.g., seeding materials and flight hours). Assumptions: lease of turbine engine aircraft equipped with acetone/silver iodide generators and ejectable flare rack for 5 months including 50 hours of seeding time, one aircraft pilot, base of operations established at a suitable airport near target area, project meteorologist stationed at an operations base (seeding decisions will be made from this location), one technician, one project dedicated 5cm weather radar. The weather radar, which would be a used version, would be purchased and installed before the beginning of the first operational season. The estimated one time charge to purchase and install this radar was $150,000. The cost estimate for the first season s fivemonth program was $472,500.
ESTIMATED INCREASES IN AVERAGE WATER YEAR STREAMFLOW AND ASSOCIATED COSTS Based upon the water years of 1974 to 2006, the estimated increase in the average annual flow at the La Puerta Gage on the Copiapo River due to the cloud seeding program, assuming a 10% increase due to seeding, would be 0.254 m 3 /sec. This value would result in ~ 8,010,000 m 3 per water year. Similar calculations for the maximum and minimum values were ~33,901,000 and 2,428,000 m 3 per water year, respectively. Estimated Cost (U.S. Dollars) of Producing Additional Streamflow on the Copiapo River at La Puerta Copiapo River Estimated Increase @ La Puerta m 3 Cost (U.S. Dollars) Minimum 2,228,272 $2.17 Average 8,010,144 $0.06 Maximum 33,901,200* $0.01 Note: 8,010,144 cubic m = 6496 acre-feet. Therefore the cost per acre-foot ~ $72 US
SUMMARY It was concluded that this feasibility/design study determined that an effective winter cloud seeding program could be established and operated for the proposed target area.
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