Snow Surveying with DWR’s Sean de Guzman


Headshot of Sean de Guzman

Sean de Guzman, manager of DWR's Snow Surveys and Water Supply Forecasting section.

Every year, the Department of Water Resources (DWR) conducts multiple manual snow surveys at Phillips Station in the Sierra Nevada. Data collected from the monthly snow surveys help determine the amount of water that will melt and run off to state reservoirs during warmer months.

Sean de Guzman is the manager of the Snow Surveys and Water Supply Forecasting section. We sat down with him to get his take on DWR’s annual snow surveys and how the information gathered impacts water management in California.

What is your background and experience?

I graduated from California State University, Sacramento with a Bachelor’s and then a Master’s Degree in Civil Engineering. I started with DWR in 2007 as an engineering student assistant, and eventually came back to DWR in a full-time role in 2011 as a water resources engineer, holding various positions after that.

In 2019, I was promoted to manager of the Snow Surveys and Water Supply Forecasting Section. Snow surveys are just a snippet of what we do – we also take that data and incorporate it into different models, that then go into the production of Bulletin 120, a forecast of seasonal run-off.

Data from the snow surveys gets incorporated into different types of models – we take that data, make sense of it, and figure out how much water will come back and fill the reservoirs in spring and summer.

What’s your role in the snow survey at Phillips Station?

This year, I will be the lead snow gauger at Phillips. I will be the main person conducting the survey, driving the tube into the snow, which measures the depth and the snow water equivalent, or how much water is in the snow, of the snowpack. This gives us an idea of how much runoff/water supply we will have for the year. We then record the measurements.

How long has the state been measuring at Phillips Station?

We have been measuring there since April 1941 – right in the exact same place. When snow courses are established, surveyors set a distance between points and record this on maps. So, we are measuring at the same spot, within a couple feet, for every single measurement dating back to the beginning. We measure at the same points every time so that we can compare different snowpacks from different years.

Why do you think the snow survey is important?

The applications for this data are unlimited – forecasting is used in flood management and in operating reservoirs. All snow survey data is hosted on CDEC, and we run models with the data to predict how much water will eventually run off and fill the reservoirs during the spring and summer months.

Snow surveys are the longest-running climate record in California. They are used for so much – climate research, forest research, gauging forest health – this is definitely a record we want to keep.

What’s one thing about the snow survey people may not know?

DWR is not the only one doing this – there are so many other agencies in California that are measuring snow. The snow survey at Phillips Station is what people see on TV or read about in the newspapers, but it is only one course of many in the state. We have over 260 courses statewide that are measured up to four times per year, as part of the California Cooperative Snow Surveys Program established in 1929. It actually predates DWR and just celebrated its 90th anniversary.

What is DWR’s role in the California Cooperative Snow Surveys Program?

DWR is the lead agency that oversees the program, but it is made up of about 50 agencies – federal, state, and local government; private organizations; utility companies; and others. Even National Parks such as Yosemite, Lassen, Sequoia, and Kings Canyon are involved.

The program was established by Assembly Bill 403 in 1929 [now California Water Code sections 228, 236], which put all these cooperative agencies together, and is how we have access to all these snow courses. This shows how important snow surveys are – 90 years later and we are still here doing the same thing.