Century-Old Scripps Pier Records Reveal Precipitation Trends

Researchers at UC San Diego’s Scripps Institution of Oceanography investigated the history of Southern California climate using a unique dataset collected at the iconic Ellen Browning Scripps Pier in La Jolla, Calif.

Led by oceanography graduate student Sierra Byrne, the team analyzed the relative freshness of the water which has been measured by hand at the pier site since 1916.  Periods when the water was less salty indicate that there was more freshwater entering the ocean from nearby streams. Inundations of freshwater took place during years when there was extreme precipitation and more streamflow.

Plotted on a graph, the history reveals the marks of climate patterns such as El Niños and La Niñas and longer patterns such as the Pacific Decadal Oscillation (PDO). The signature of a 30-year-long negative phase of the PDO from the 1940s to 1970s when waters in the eastern Pacific Ocean were relatively cool reveals itself in a pattern of minimal salinity variation in pier samples. 

“This provides us with an extremely valuable dataset that we use to look for interannual to decadal variability in winter salinity,” said Byrne. “This is possible because of the connectivity between rain, streamflow, and coastal ocean dynamics that spread low salinity waters through freshwater plumes.”

Though there are other ways to observe past climate trends, the researchers say this approach is novel because even a location like La Jolla, which is not immediately adjacent to any river, can still pick up the signal of heavy streamflow. The nature of storms in California tends to push freshwater south when it enters the ocean so in the case of Scripps Pier, the nearest freshwater flows come from Los Peñasquitos Lagoon seven kilometers (4.3 miles) to the north and the San Dieguito River 12 kilometers (eight miles) to the north.

“This highlights the value of coastal sea surface salinity data as a way to connect the coastal ocean, local streamflow, and atmospheric variability,” said Byrne. “Typically, surface water temperatures are used for detecting shifts in climate phases, and through the influence on winter precipitation in Southern California we show that surface salinity also reflects these climate phases.”

The study appears today in the journal Communications Earth & Environment. The California Department of Parks and Recreation, Natural Resources Division, and the U.S. Army Corps of Engineers funded the work.

Scientists, aquarists, and technicians have all played a role in collecting data from Scripps Pier since 1916, when the original pier was constructed. Measurements of water temperature and salinity are taken at the water’s surface and closer to the bottom via collection bottles that are lowered from a structure at the end of the pier. These readings are the oldest known continuous record of Pacific Ocean conditions. Today, nine other stations join Scripps Pier in the statewide Shore Stations program.

“We are grateful that California State Parks has continued its long-term support of these crucial Scripps Shore Stations time series of salinity and temperature at 10 stations extending the length of our state,” said Reinhard Flick, co-principal investigator of the Shore Stations program. “Only long, continuous, and consistently measured data like these from Scripps Pier make it possible to quantify decades-long climate variability. Old time series that began before large and fast climate change effects manifested are especially important to determine the amount and rate of current and future climate changes.”

This study used Scripps Pier data collected between 1916-2021. Byrne said that data collected since that time frame, including the 2023 PiNC (Plumes in Nearshore Conditions) experiment could build on it. Such research into the size and direction of freshwater plumes in the ocean could inform tracking of coastal pollution and improve the safety of beach communities.