Changes in climate continue to make surveying watersheds tricky. ‘But we can change that’

In April 2015, I escorted then-Gov. Jerry Brown to Echo Summit, where we ceremoniously plunged a metal pole onto the dry, bare earth that typically would have been covered by snow but wasn’t that year. That spring, we were in the depths of a record-setting drought.

If you’re among the many Californians who remember the photo of that survey, you’ll probably recognize me. I’m the one wearing a ball cap with “DWR” plastered on the front. Until my retirement last December, I’d been measuring snow in California for nearly 40 years. As chief of the Cooperative Snow Surveys Program, I’ve had a front-row view of how changes in the state’s needs – and climate – have begun challenging our traditional snow measurement and forecasting methods.

More than a century ago, Dr. James E. Church developed methods that California now uses to measure snowpack and forecast how much water will enter our rivers and lakes each spring. These forecasts have benefited California by allowing for the efficient management of water for our cities and farms, our environment, and for the generation of clean hydroelectric power.

But the current forecasts rely on statistical descriptions of historical conditions. Those statistics are used to extrapolate the handful of “pixels” we can collect with manual surveys to create a “full picture” for watersheds that get surveyed. In my 40 years at the California Department of Water Resources, I have seen changes in climate that have convinced me that the full picture is changing and our extrapolation methods are losing value rapidly. This is especially true in extreme years, wet or dry – such as 2015, when the statistics are just not going to be accurate enough to meet our growing water management needs.


But we can change that. For the past six years, California has collaborated with local water districts, flood agencies, power generators, environmental groups and NASA’s Jet Propulsion Laboratory to fund and operate the Airborne Snow Observatory. This program has allowed us to take aerial measurements of the snowpack on every square foot for several Sierra Nevada watersheds and turn them into runoff forecasts that are 96 percent to 98 percent accurate.

Dale Kolke California Department of Water Resources
Senate Bill 487

California’s initial investment in the program has already begun to benefit operators in the Tuolumne Basin, where more than 150,000 acre feet of water was saved from spilling last year due to this program because water managers knew precisely how much water was stored in the snow.

Since 2016, agencies working on the San Joaquin River have used the data to optimize releases made to restore salmon. State and local flood agencies have incorporated it into their efforts to reduce public safety risks during the winter flood season. It holds untold more benefits for optimized hydroelectric power generation and groundwater recharge. It’s even useful for forest management. For example, it allows us to pinpoint tree mortality hotspots.

The aerial snow survey program supported by SB 487 is a game changer. It is, without a doubt, the most significant development in the history of snow surveys. In years when we must make do with less water, it’s crucial to know exactly what we have.

Frank Gehrke is the retired chief of California Cooperative Snow Surveys for the Department of Water Resources.
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