Wyoming Weather Modification Pilot Program (WWMPP)
Executive Summary
The Wyoming Weather Modification Pilot Program (WWMPP) was a comprehensive study conducted from 2005 to 2014 to assess the feasibility of increasing Wyoming's water supplies through winter orographic cloud seeding. This executive summary provides an in-depth overview of the project's design, implementation, and key findings.
1. Introduction and Background
1.1 Project Overview
- Duration: 2005-2014
- Funding: Wyoming Water Development Commission (WWDC)
- Primary Goal: Determine the viability of cloud seeding for augmenting water supplies in Wyoming
1.2 Target Areas
The WWMPP established cloud-seeding research programs in three Wyoming mountain ranges:
- Medicine Bow Range
- Sierra Madre Range
- Wind River Range
1.3 Orographic Cloud Seeding Concept
Orographic cloud seeding is designed to enhance precipitation in winter storms with inefficient precipitation processes due to a lack of natural ice nuclei.
Key points:
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Uses ground-based generators to produce silver iodide plumes
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Plumes are transported by ambient winds into orographic clouds
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Aims to increase precipitation by creating additional ice crystals
1.4 Project Structure
- Operations: Weather Modification, Inc. (WMI)
- Evaluation: National Center for Atmospheric Research (NCAR)
- Additional Contributors:
- University of Wyoming
- Desert Research Institute
- Heritage Environmental Consultants
- University of Alabama
- University of Nevada Las Vegas
- University of Tennessee
1.5 Oversight and Collaboration
- Technical Advisory Team (TAT) established
- Local stakeholders engaged throughout the project
2. Design of the WWMPP
2.1 Primary Evaluation Method
The main evaluation tool was a Randomized Statistical Experiment (RSE) focusing on the Medicine Bow and Sierra Madre Ranges.
2.2 Additional Evaluation Components
- Permits for siting seeding generators and instruments
- Numerical modeling studies
- Physical measurements of silver iodide
- Verification of silver iodide targeting
- Climatological context of seeding opportunities
- Hydrological modeling of cloud-seeding impacts
- Environmental monitoring of silver
- Studies of extra-area effects
2.3 RSE Design
- Duration: Six winter seasons (2008-2014)
- Design Process: Iterative, involving peer reviews and facility adjustments
- Experiment Type: Crossover design
- One range randomly selected for seeding
- Other range served as "control"
2.4 Seeding Criteria
- Temperature < -8°C (+17°F) near mountain top
- Favorable wind direction for silver iodide transport
- Presence of supercooled liquid water
2.5 Facilities and Equipment
Equipment | Purpose |
---|---|
Atmospheric sounding unit | Measure vertical profile of atmosphere |
Microwave radiometers | Detect supercooled liquid water |
Ground-based seeding generators | Produce silver iodide for seeding |
High-resolution snow gauges | Measure precipitation in target and control areas |
High-resolution weather forecast model | Predict atmospheric conditions |
2.6 Experimental Design Details
- Case Duration: 4 hours
- Response Variable: 4-hour precipitation accumulation
- Test Statistic: Root regression ratio (RRR)
- Estimated Cases Needed: 65-70 per year for 5-6 years
2.7 Permitting and Approvals
- Federal: U.S. Forest Service (USFS) special use permit
- State: Wyoming Office of State Lands and Investments
- Private: Landowner permissions
- Additional: Wyoming State Engineer's Office, NOAA
3. Physical, Statistical, and Modeling Analyses
3.1 Physical Studies
3.1.1 Trace Chemical Analysis
- Purpose: Determine silver incorporation from cloud seeding
- Finding: Variable results, but generally lower than Australian studies
3.1.2 Ground-based Measurements
- Instrument: Acoustic ice nucleus counter (AINC)
- Duration: First three project years (2008-2011)
- Key Finding: Confirmed silver iodide reaching intended target
3.1.3 Aircraft Studies
- Conducted by: University of Wyoming
- Initial Results: Up to 25% increase in precipitation for 7 lightly precipitating storms
- Follow-up Studies: Less pronounced effects, highlighting need for larger sample sizes
3.2 Modeling Studies
- Model Used: Weather Research and Forecasting (WRF) with NCAR cloud-seeding module
- Seasons Simulated: 2009-2010, 2011-2012, 2013-2014
- Key Results:
- Simulated seeding effects between 10-15% in both mountain ranges
- Model performance verified using radiometer, snow gauge, and sounding data
3.3 Statistical Studies
3.3.1 Primary Analysis
- Total RSE Cases: 154
- Cases Included in Analysis: 118
- Primary Result:
- RRR = 1.03
- p-value = 0.28
- Interpretation: 3% increase in precipitation, 28% chance of occurring by chance
3.3.2 Secondary Analyses
- Unintended Downwind Effects:
- 18 cases with downwind impacts identified
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Removing these cases increased RRR to 1.09
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Silver Iodide Reaching Target:
- 21 cases with confirmed silver iodide at target
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Removing these cases increased RRR from 1.03 to 1.04
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Generator Hours Stratification:
- RRR increased to 1.17 for cases with ≥27 generator hours
- Suggests sufficient seeding agent necessary for detectable effect
Note: These secondary analyses, while informative, cannot claim statistical significance due to post-hoc nature.
4. Climatology of Seeding Opportunities
4.1 Methodology
- Model: 8-year high-resolution regional climate model (2000-2008)
- Forced by: Re-analysis meteorological data
4.2 Key Findings
- Atmospheric conditions met seeding criteria <1/3 of winter time
- Precipitation occurred ~50% of the time when conditions met criteria
- ~30% of wintertime snowpack would have been seeded under RSE conditions
5. Streamflow Impacts
5.1 Hydrological Modeling
- Model: Variable Infiltration Capacity (VIC)
- Study Area: North Brush Creek watershed (Upper North Platte River Basin)
- Baseline Performance: Within 1% of observed snowmelt-driven streamflow (2001-2008)
5.2 Modeled Impacts
For 5-15% seeding impact on winter precipitation:
- Streamflow Increase: 95-288 AF/sq-mi over 8 years
- Seedable Area: ~390 sq-mi (elevation > 9,000 ft)
- Potential Impact Area: 30-80% of seedable area
5.3 Example Scenario
For 10% seeding effect impacting 60% of the basin:
- Additional Water Generated: 7,100 AF/year on average
- Percentage Increase: 1.8% in Wyoming area of North Platte River Basin
6. Cost Analysis
6.1 Operational Cost Estimates
Option | Annual Cost Range |
---|---|
Sponsor-owned equipment | $375,500 - $526,400 |
Contractor/leased operation | $420,600 - $571,500 |
Evaluation component | Additional $222,700 |
6.2 Cost per Acre-Foot
For 10% efficiency and 60% basin coverage:
- Low-cost estimate: ~$53/AF
- Range: $35-107/AF (5-15% efficiency)
Comparison: Wyoming markets North Platte water at $30-75/AF for temporary uses
7. Environmental Impacts
7.1 Trace Chemistry Analyses
- Samples: Water and soil from all three ranges
- Frequency: Following each operational season
7.2 Key Findings
- Water: Silver concentrations in parts per trillion
- Soil: Silver concentrations in parts per billion
- Interpretation: Negligible environmental impact, far below hazardous levels
8. Extra-Area Effects
- Method: WRF model simulations
- Key Finding: Net effect outside intended targets small to zero (<0.5%)
- Caveat: Based on model results, not validated by observations beyond target areas
9. Conclusions
- Ample supercooled liquid water existed at conducive temperatures
- Cloud seeding appears viable for augmenting water supplies in Medicine Bow and Sierra Madre Ranges
- Statistical analysis suggests 3-17% increase for well-seeded storms
- ~30% of winter precipitation fell from storms meeting seeding criteria
- Modeling studies showed 10-15% positive seeding effects
- Potential streamflow increases of 0.4-3.7% in Wyoming's North Platte River Basin
- Estimated water cost: $27-$427 per acre-foot
- Negligible environmental impacts
- Minimal extra-area effects
10. Recommendations
- Barrier Identification: Conduct long-term climatological studies
- Program Design: Optimize seeding methods and generator placement
- Operational Criteria: Utilize real-time data and forecasting
- Evaluation: Combine modeling and high-resolution measurements
- Program Management: Engage stakeholders and pursue collaborative opportunities