Historical and Future Potential for Ground-Based Orographic Glaciogenic Cloud Seeding in the Interior Western United States

Water resources are limited in the Interior Western USA, and water availability is a major concern in a warming climate. Most water use is derived from cold-season orographic precipitation, much of it stored as snow until spring. Glaciogenic cloud seeding can be used as a tool to enhance precipitation and the seasonal snowpack in the mountains. Here, the amount of time and locations where glaciogenic seeding can be effective in the Interior Western USA are evaluated. Ten years of regional climate model output are evaluated for the conditions favorable for ground-based glaciogenic cloud seeding. This 4 km simulation was driven by the CFSR reanalysis. We examine three factors impacting ground-based cloud seeding efficacy: temperature, cloud liquid water path, and the ability of near-surface air to be mixed in the boundary layer and be carried across a downwind mountain in a historical and future simulation. The likelihood of blocking is assessed using a novel Froude number approach that is spatially continuous and, at each location, depends on the local wind and stability profiles. The most seedable places generally are over the highest terrain, with generators to be placed in the foothills above shallow inversions that prevent the effective dispersal of seeding material from the ground. This is consistent with current practice, although the analysis reveals several mountain ranges that currently are not seeded but have good potential.

The regional climate simulation is repeated for a future climate, representing conditions around ~2060, assuming the pseudo global warming technique with CFSR conditions perturbed by the IPCC RCP8.5 scenario (relative to current). Seedability decreases in all mountain ranges, but the relative changes in this future climate are generally small, except for the mountains in Idaho and far western Montana, where warming significantly reduces the time periods cold enough for glaciogenic seeding