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<p>James Tilley. COURTESY PHOTO.</p>

James Tilley. COURTESY PHOTO.

Jeff Tilley joined Nevada’s Desert Research Institute in February as its director of weather modification. In his new job, Tilley will design and operate the institute’s cloud seeding program.

It augments snowfall in mountainous regions that supply water to Nevada. One target is the mountains of the upper Colorado River basin, which provide runoff to the Colorado River, which in turn supplies Las Vegas with 90 percent of its drinking water.

DRI scientists estimate that annual augmented snow wat er has averaged 64,000 acre-feet during the last 15 years. That’s about 21 billion gallons, or enough to supply 64,000 households (of four people each) for a year. DRI’s seeding operations in Nevada are funded by the Southern Nevada Water Authority, the Bureau of Reclamation, the Western Regional Water Management Fund and the Truckee Meadows Water Authority.

What are the basics of cloud seeding?

Cloud seeding takes several forms, depending on the types of clouds that are being seeded. The types of clouds seeded are usually a function of the goal of the sponsors of seeding operations.

The overall goal of Nevada water authorities is to increase the amount of water that can be stored within reservoirs, groundwater and other types of storage. As a result, seeding activities focus on wintertime precipitating clouds. Such clouds typically contain significant numbers of suspended supercooled water droplets (liquid water at subfreezing temperatures) and quite small numbers of tiny particles (called ice nuclei) that serve as sites where ice crystals form and grow to become snowflakes.

When we seed these wintertime clouds, we introduce large numbers of particles that can serve as ice nuclei. That allows for the supercooled water to turn into ice crystals, which then grow into snowflakes large enough to precipitate to the ground.

How promising have the results been?

At DRI, we conservatively estimate that the amount of additional water mass generated by our seeding efforts averages 10 percent of what might fall without any seeding. Thus, we would add 30,000 acre feet of water to a drainage basin that might otherwise receive 300,000 acre feet without seeding.

What motivated you personally to get involved in this avenue of research?

I like to see science efforts benefitting society in tangible ways. During the past decade more of my research has focused on cloud processes as well as finding better ways to predict cloud and precipitation systems. The extension to cloud seeding efforts came very naturally, especially after participating in a cloud seeding project in Saudi Arabia several years ago.

Are there opportunities to scale up the program for bigger results?

The opportunities are really only limited by the available funding from various sources. With adequate funding, we could conceivably perform seeding on most mountain ranges in Nevada that are wide enough (more than 25 miles wide) and reach sufficient altitudes (8,500 feet or higher).

What is the goal of the cloud-seeding program? Is it expected to produce real results, in terms of increased precipitation and water into the Colorado River and Sierra Nevadas, or is the focus on research?

Our program, with the exception of one project in Wyoming, is considered operational in that getting real results is the focus. We would like to be able to do more research to optimize our efforts, but we cannot do that research at the current levels of funding.

In a similar vein, do you see yourself as a researcher, primarily, or as an engineer of the weather?

I consider myself an applied meteorologist and as such, I wear multiple hats, all of which really lead to an eventual societal gain. There are engineering aspects to the operational program, but, where possible, science research plays a role, as well. My goal as the new DRI weather modification director is to try to expand the research elements of the program such that (1) we can optimize our efforts and make them even more cost-effective; and (2) the research into cloud and precipitation systems can be applied to improve our understanding and prediction of the Earth climate system which we, as mankind, both inhabit and modify.

Is global climate warming a real phenomenon, and is it driven by anthropogenic forces?

The evidence for a warming climate on the whole since industrialization has continued to mount, and it has become generally accepted by most in the atmospheric-science community that the warming is real and not an artifact of the data analysis. However, because the climate system, and its components (atmosphere, ocean, sea ice and land) are dynamic, nonlinear systems separately and in the whole, one cannot expect warming to be easily depicted by a continuous linear trend. This also clouds (pun intended) the assignment of part, or all, of this warming to anthropogenic forces. We know enough about atmospheric chemistry to know that the “greenhouse effect” is a real process that can affect the climate as postulated, but it is not the only process operating. A longer data record than we currently have is required to definitively attribute a specific percentage, or all, of the real warming trend to anthropogenic forcings. Until then, we can say anthropogenic greenhouse forcings exist and are one mechanism that is operating to modify the present climate.

There has been quite a bit of discussion in the popular media about “hacking the planet,” about the idea that we as humans have made massive changes to our environment, and so we need to consciously intervene. Isn’t that what you and your colleagues are doing? And is this the future for mankind on Earth?

While cloud seeding represents a conscious effort to modify the weather, one can’t necessarily consider it a response to other changes that may or may not have occurred at the hand of mankind. Even without any anthropogenic climate forcings, humans may well have chosen to dwell in desert climate zones and put stress on water resources, and cloud seeding would still have been done. Whether this is the future for mankind is not for me to say … it depends on the interaction of future climates with socioeconomic patterns and forcings that are difficult to predict over time.

Isn’t there an inherent danger in muddling with the weather? That is, weather and climates appear to be huge systems. If we change one thing, be it more snow in the Rockies or a butterfly’s wings in the Amazon, isn’t there the possibility of unforeseen consequences?

While it is true that the atmosphere and the climate system are nonlinear, chaotic systems, there are many aspects of atmospheric behavior that, on certain scales, can be considered more deterministic and linear — an aspect that was not presented well in the movie The Butterfly Effect, which helped to popularize chaos theory. Modern cloud seeding operations work on a small enough scale that the behavior is more deterministic and linear, such that the largest positive impacts are local.

Cloud seeding seems to be an expensive fix for the water problem.

Cloud seeding is actually much less expensive and [more] cost-effective, compared to the alternatives, than is sometimes believed.

DRI’s cloud seeding efforts cost an average of $12 per acre-foot. By contrast, water authorities’ costs to deliver water range from $70 to $100-plus per acre-foot. Desalinization plants cost hundreds of millions to build and operate; Saudi Arabia has built several in the past but has now turned to seeding operations, since they cost two to three orders of magnitude less per year to operate. Pipelines are also much more expensive to maintain than seeding operations and ultimately don’t add water to the system, they simply redistribute it. Voluntary conservation efforts are difficult to be effective due to nonuniform compliance, while mandatory conservation costs more per capita in terms of enforcement costs, fines and potential negative economic consequences to the community (individuals and businesses leave or are deterred from entering the community due to prohibitive costs). Of course, one could simply say that people shouldn’t live in areas where water resources are scarce, but it’s too late for that.

Cloud seeding has demonstrated itself as a cost-effective approach to water management, as can be testified to by communities in Nevada (e.g., Reno, Carson City, Elko, Battle Mountain, Winnemucca) that have benefited from seeding operations.

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