Snow surveys: a critical tool to maximize water supply

Funding is needed for the full suite of snow survey tools that meet 21st century challenges

Every drop of water in California has never been more important. Climate change, tightening constraints from diverse users, and groundwater restrictions in California under  SGMA  present challenges for water managers balancing supply from year to year. Adequate and consistent funding for the diverse portfolio of complementary snow survey measurements would give water managers a comprehensive toolkit needed to tackle these 21st century challenges and maximize every drop for people, farms, environment, and our groundwater aquifer.

Water management begins in the 1,500 square mile Kings River watershed in the Southern Sierra Nevada, where on average 1.75 million acre-feet of water supply for portions of Fresno, Kings, and Tulare counties is found stored as snow. This supply is extremely variable and in wet years can exceed 4 million acre-feet, swinging below 400,000 acre-feet in the driest years.

1

Snowpack: nature's water storage

As snow falls in the mountains over the winter months it is naturally stored on the peaks until melting when warmer weather arrives.

2

Kings River runoff

Snowmelt makes its way through the upper Kings River.

3

Pine Flat Reservoir

Kings River runoff is stored in Pine Flat Reservoir.

4

Water for fish

Water releases maintain steady flows to meet needs of the lower Kings River fishery.

5

Water for irrigation

Water makes its way down the Kings River and is diverted to the water rights holders for irrigated agriculture deliveries.

6

Water for urban users

Several of the water rights holders on the Kings River serve municipal water needs, delivering high quality water for urban use.

Using the available snow survey tools to forecast supply helps water managers make decisions including how much and when to release for all purposes. In California, water demand has dramatically increased in the last 60 years.

On the flipside of growing water demand, water supply availability and timing is impacted by climate change, increasing water management complexity. Every water management decision made in California relies on accurate forecast information. The better initial information the better the final results. Climate science and monitoring are ever evolving. Our forecasting tools need to evolve as well.

According to UCLA climate scientist  Daniel Swain , "having wider swings between drought and flood - that might actually be the new normal" ( PPIC ). Steve Haugen, Kings River Watermaster, expresses variability coupled with warmer temperatures creates timing hurdles for water managers.

Adjusting to the new normal could mean adjusting to change in natural water storage capacity found in snowpack, as snow melt patterns change and some precipitation falls as rain rather than snow. This could cause reservoirs to fill quicker and earlier triggering flood release to make room for fast-approaching runoff that otherwise would have been stored in snowpack. Intense precipitation events, " atmospheric rivers ", compound these effects ( UCSD Scripps Oceanography ).

To meet the challenges water managers need data provided by a suite of snow survey tools available today. However, a lack of secure funding for modern snow surveying puts efficient management of a limited resource at risk.

The ideal combination of airborne LiDAR snowpack measurements through programs like  California Department of Water Resources  Airborne Remote Sensing for Snowpack (ARSS) program paired with traditional on-the-ground snow surveying and automated snow sensors gives water managers the most accurate data to analyze how much water will reach Pine Flat Reservoir and when, allowing the optimization of the various demands for previous water supplies.

Airborne snow depth measurement flights can cover the entire Kings River watershed with approximately 400 million measurements taken over a 12 hour period, completely and accurately assessing snow depth across the entire snowpack area. Ten flights per water year would provide optimal high-resolution snowpack information throughout the snow accumulation and melt periods.

Funding for airborne LiDAR snowpack measurement flights, the tool with the highest accuracy, has been inconsistent.

In water year 2020, funding was secured to conduct three airborne flights in the Kings River watershed. In water year 2021, funding was secured via the California Department of Water Resources to conduct only two flights.

In addition to airborne LiDAR flights, traditional ground sampling at 23  California Cooperative Snow Survey  sites throughout the 1,500 square mile watershed provide snow depth and water content measurements that when used in concert with flights, modelling, and automated snow sensors, contribute to the daily understanding and analysis of the snowpack. Each of the processes are complementary and essential to provide robust forecasting that meets 21st century water management decisions.

The Kings River Water Association (KRWA), consisting of 28 member units with water rights on the Kings River, contributes to annual ground surveying efforts as part of the  California Cooperative Snow Survey  program.

The KRWA promotes the evolution of the program to introduce new technology and techniques to strengthen the accuracy of snowpack analysis across California, including the Kings River watershed. This would mean greater investment through state and/or federal funds for satellite and airborne data beyond traditional ground surveys and sensor network.

The available snow survey tools helps water managers forecast supply decisions including flood control releases from the reservoir. 

Using flood water for groundwater recharge is a hallmark strategy of many local agencies to balance groundwater supply under California’s Sustainable Groundwater Management Act (SGMA). 

Forecasting supply also helps cities plan their water management strategy, allowing urban areas to offset groundwater pumping to meet water needs of homes, businesses, and industry.

Informed reservoir operations afforded by snow surveys leads to the most efficient use of every drop for people, farms, the environment, and aquifer sustainability. The need to capitalize on available water supply means precision at every stage, from watershed to end use.

Despite the value provided from the full suite of snow survey tools, funding is a hurdle for the program. Beyond local funding for traditional ground sampling, additional state and federal investment is needed for robust data collection that all water managers in the Kings River region, and across California, need to maximize every drop.