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Literature Review and Scientific Synthesis on the Efficacy of Winter Orographic Cloud Seeding

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Literature Review and Scientific Synthesis on the Efficacy of Winter Orographic Cloud Seeding Statement on the Application of Winter Orographic Cloud Seeding For Water Supply and Energy Production Literature Review and Scientific Synthesis on the Efficacy of Winter Orographic Cloud Seeding A Report to the U.S. Bureau of Reclamation January 2015 Prepared by David W. Reynolds CIRES Boulder, Co 1 Technical Memorandum This information is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the Bureau of Reclamation. It does not represent and should not be construed to represent Reclamation’s determination or policy. As such, the findings and conclusions in this report are those of the author and do not necessarily represent the views of Reclamation. 2 Statement on the Application of Winter Orographic Cloud Seeding For Water Supply and Energy Production 1.0 Introduction ........................................................................................................................ 5 1.1. Introduction to Winter Orographic Cloud Seeding .......................................................... 5 1.2 Purpose of this Study........................................................................................................ 5 1.3 Relevance and Need for a Reassessment of the Role of Winter Orographic Cloud Seeding to Enhance Water Supplies in the West ........................................................................ 6 1.4 NRC 2003 Report on Critical Issues in Weather Modification – Critical Issues Concerning Winter Orographic Cloud Seeding – ........................................................................................... 8 1.4.1 Response to NRC Report from Weather Modification Community ............................ 10 1.5 Brief History of Federal and State Authorizations for Weather Modification .................... 12 1.6 Current Policy Statements from American Meteorological Society and World Meteorological Organization on Efficacy of Winter Orographic Cloud Seeding ..................... 14 1.7 Generalized Concepts of Winter Orographic Cloud Seeding ............................................. 16 1.7.1 The Initiation, Growth and Fallout of Snow in Winter Orographic Clouds ........... 17 1.7.2 Transport and Dispersion of Seeding Material ............................................................. 24 1.7.3 Silver in Snow Concentrations and Other Targeting Validation Methods ................... 27 1.7.4 Extended Area Effects from Winter Orographic Cloud Seeding........................... 28 1.7.5 Statistical Analyses ..................................................................................................... 33 1.8 Summary ............................................................................................................................. 34 2.0 Review of Relevant Winter Orographic Cloud Seeding Research Projects Since NRC 2003............................................................................................................................................... 39 2.1 Snowy Mountain Confirmatory Experiment Australia ........ Error! Bookmark not defined. 2.1.1 Follow-on three year randomized seeding ................................................................. 49 2.2 Wyoming Weather Modification Pilot Project .................................................................... 53 3.0 Short-term Physical Process Studies of Efficacy of Winter Orographic Cloud Seeding ....................................................................................................................................................... 59 3.1 Utah Exploratory Propane Seeding Trials ........................................................................... 59 3.2 Exploratory Physical Process Studies in Winter Orographic Clouds in Japan ................... 64 3.3 Exploratory Physical Studies of AgI Ground Based Seeding in Wyoming ........................ 70 3.3.1 ASCII 12 ....................................................................................................................... 70 3.3.2 ASCII 13 ....................................................................................................................... 86 3.4 Application of Numerical Modeling in the Conduct and Evaluation of Winter Orographic Cloud Seeding ........................................................................................................................... 91 3.4.1 NCAR WRF Modeling for Winter Orographic Cloud Seeding ................................... 92 3.4.2 Modeling and Observations over the Tahoe Truckee and Walker River Basins in Nevada ................................................................................................................................. 107 4.0 Statistical Analyses of Non-randomized Operational Seeding Programs ..................... 115 4.1 Introduction ....................................................................................................................... 115 4.2 Historical Evaluation of 11 Operational Winter Seeding Programs in California ............ 116 4.3 Historical Evaluation of the Vail Colorado Operational Seeding Program ...................... 118 5.0 Summary and Conclusions ................................................................................................ 120 5.1Developments in Understanding Key Uncertainties .......................................................... 121 5.1.1 What is the location, duration, and degree of supercooling of cloud liquid water in winter orographic clouds? ................................................................................................... 121 5.1.2 Are their man-made pollutants or natural aerosols/particulates impacting the target clouds that could modify the cloud droplet spectra/IN concentrations to impede seeding effectiveness? ...................................................................................................................... 122 3 Technical Memorandum 5.1.3 Are their significant enough differences in maritime influenced winter orographic clouds versus continental orographic clouds that strongly influence the natural precipitation process? ............................................................................................................................... 123 5.1.4 Are there numerical models that can be run in real-time utilizing project field observations to guide seeding decision making? ................................................................. 123 5.1.5 What is the best seeding agent to use based on SLW temperature regime and what is the best way to deliver the seeding agent? .......................................................................... 124 5.1.6 What is the necessary density and location of ground-based dispensers and what is the dependency on seeding agent used? .................................................................................... 124 5.1.7 What observing systems are needed and at what spatial and temporal frequency to adequately target seeding impacts? ..................................................................................... 125 5.1.8 What are the observing systems, either in-situ or remote sensing, that can observe and track a seeding plume from initiation to fallout? What are the benefits and limitations of each? .................................................................................................................................... 126 5.1.9 What is the resolution and spacing required of recording snow gauges within the intended target area and downwind target area? ................................................................. 127 5.1.10 If silver iodide is the seeding agent, what are the benefits and limitations of sampling the silver concentration in the snow prior to spring melt to validate that a significant portion of the winter seeding impacted the target area? .................................................................. 127 5.1.11 What is the best design of the seeding program to reduce uncertainty and insure meaningful statistical results?.............................................................................................. 128 5.1.12 What are the best statistical methods to apply to achieve statistical significance and reduce Type I and II errors? ................................................................................................ 129 5.1.13 Benefits and limitations of a reanalysis of operational cloud seeding projects? ...... 129 5.2 Effectiveness of Winter Orographic Cloud Seeding ......................................................... 131 5.3 Summary and Conclusions about Scientific Efficacy .................................................. 132 5.3.1 Next Steps ................................................................................................................... 135 5.3.2 Final Conclusion ......................................................................................................... 135 6.0 References ............................................................................................................................ 135 4 Statement on the Application of Winter Orographic Cloud Seeding For Water Supply and Energy Production 1.0 Introduction 1.1. Introduction to Winter Orographic Cloud Seeding In its most basic form, artificial seeding of clouds for precipitation enhancement can be divided into two broad categories: 1 – cloud seeding to enhance rainfall i.e. summer convection, 2 – winter orographic cloud
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