By Sean Nealon, OSU release - CORVALLIS, Ore. – Measuring mountain snowpack at strategically selected hotspots consistently outperforms broader basin-wide mapping in predicting water supply in the western United States, a new study found.  Researchers analyzed more than 20 years of snow estimates and streamflow data across 390 snow-fed basins in 11 western states to evaluate two potential strategies for expanded snow monitoring. This analysis revealed locations the researchers are calling hotspots — localized areas where snowpack is not yet measured but is especially predictive of water supply — and their importance.  They found that hotspot monitoring can improve water supply predictions in most basins, with typical gains of 11-14% compared to 4% from basin-wide mapping of snow.  “Measuring snow in the right places can benefit forecasts more than measuring it everywhere,” said lead author Mark Raleigh, a snow hydrologist at Oregon State University. “This could guide our thinking about how snow monitoring might evolve to become more optimal for water forecasting.”  Snowmelt is a key water source for about two billion people globally, including in many agricultural regions, such as the western United States. On average, about half of the water in western streams is driven by snowmelt, Raleigh said.  “Our findings can help water agencies make informed decisions for more efficient water monitoring,” Raleigh said.  For about 100 years, statistical water supply forecasting in the west has relied on snow measurements at ground-based stations. The researchers analyzed data from these snow stations and found that they accurately predict year-to-year shifts in water supply, but the stations are sparsely located and sample a small area.  As a result, there is untapped potential to improve forecasts through expanded snow monitoring across a basin, though the predictive value of each location is not usually known in advance. The study provides a framework to assess a basin’s potential for improvements and identify where the greatest and smallest gains might be found.  Basin-wide surveys are the most comprehensive method to quantify the total amount of snow in a basin. This total snow volume over a basin is most accurately measured from airplanes. Satellite data can also support snow estimates over large areas. However, deploying these types of large-scale mapping technologies can be costly compared to the sort of localized monitoring included in this study.  In the new study, published in Communications Earth & Environment, the team compared the water supply predictive ability of the basin-wide surveys versus the hotspot approach. The researchers found that although both strategies can enhance water supply predictions, the hotspot approach typically yields better or similar improvements, despite measuring snow over a much smaller portion of the basin.  “Focusing new snow measurements at hotspots is a cost-effective alternative to basin-wide surveys, with potential for more accurate water forecasts,” Raleigh said. “This efficiency is critical as we move into a time when budgets are tightening and the demand for reliable water information remains high.”  Co-authors of the paper are Eric Small and Karl Rittger, University of Colorado Boulder; Edward (Ned) Bair, Leidos Inc., a national security and health company; and Cameron Wobus, CK Blueshift, a consulting group focused on the intersection of climate and water.