California’s water supply hinges heavily on its snowpack—often called the state’s natural reservoir. Snow that accumulates in the Sierra Nevada during winter slowly melts in spring and summer, feeding rivers and reservoirs across the state. This snowmelt supports the natural environment, agriculture, powers hydroelectric generation, and provides drinking water to millions. But to manage this precious resource, accurate data on how much snow is in the mountains—and how much water it represents—is essential. That’s where the Airborne Snow Observatory (ASO) flights come in.
Operated by the Department of Water Resources (DWR) in partnership with state and local water agencies, ASO flights use advanced LiDAR and spectrometer technology to measure snow depth and to calculate snow water equivalent (the amount of water stored in the snowpack) with unprecedented accuracy.
The value of this data can’t be overstated. For water managers, precise snowpack measurements are the foundation for predicting how much snowmelt runoff will occur—and when. This directly informs decisions about reservoir releases, flood control, irrigation scheduling, and drought preparedness. For example, releasing too much water early in the season based on an overestimate of snowpack can leave reservoirs empty when the melt runs dry. While in wet years, knowledge of large snowpack allows water users time to make early releases of flood flows at lower, and safer, levels to reduce flood risk.
In recent years, as climate change accelerates the volatility of snow accumulation and melt timing, ASO data has become even more critical. Snowpack levels can fluctuate drastically due to warmer winters and earlier thaws, making past trends unreliable for future planning. ASO’s detailed measurements allow for dynamic, responsive water management in an increasingly unpredictable environment. Because of this forecasting advancement, ASO has been identified as a solution in California’s Water Resilience Portfolio, which provides a roadmap to building the State’s water resilience.
Moreover, ASO supports broader environmental goals by improving habitat management for endangered fish species and maintaining instream flows. It enables a fine-tuned balancing act between human and ecological needs.
Simply put, ASO flights give California water managers the tools to make better informed, more sustainable decisions. As the state grapples with a future of water scarcity and climate extremes, expanding the use of ASO technology may be one of the smartest investments the government can make to ensure resilience and equity in water distribution. The snow may fall in the mountains, but the impact of measuring it reaches all of California.
Despite the benefits of ASO, the State of California has shifted from building the program up, to slashing funding in the current budget. The California state plan was to invest $40 million per year into these crucial measurements, which would cover all snow-dominated watersheds in California. The State has been operating a portion of those watersheds on a budget of $15 million. Current planning for FY 2026 shrinks the program budget to just $4 million. This budget cut will limit the State’s own runoff forecast resilience and will have trickle down impacts on federal runoff forecasts, both of which are essential for water managers and flood control operations, putting life and property at risk.
