How winter weather in the U.S. is impacted by El Niño and La Niña. Infographic courtesy of NOAA.
October 20, 2021
By Jenna Allred, Senior Manager of Climate Change Adaptation
With winter just around the corner, The Santa Lucia Conservancy is planning next year’s land management projects and priorities. As current and future climate conditions control all we do on The Santa Lucia Preserve, we must adapt to the El Niño-Southern Oscillation (ENSO) phases and how they impact California’s Central Coast. ENSO is a natural climate pattern that influences the amount of precipitation that occurs in California during the rainy season and shifts between three phases every two to seven years: El Niño, La Niña, and Neutral. Each phase is associated with differences in ocean temperature, winds, surface pressure, and rainfall.
Last winter, we experienced the La Niña phase here in California. This phase is characterized as the “cool phase” meaning that the ocean temperature is cooler compared to the other phases. During La Niña, surface winds are stronger across the Pacific Ocean, and they push the warm water towards Asia. This causes an upwelling of cooler, nutrient-rich water in the eastern Pacific. As more cool water accumulates, the jet stream over the continental United States is pushed northwards, leading to wetter winters in the Pacific Northwest and drought conditions in Central and Southern California.
The opposite phase to La Niña is El Niño, the “warm phase.” El Niño is characterized by weaker surface winds keeping the warm water in the Eastern Pacific. Warm ocean temperatures lead to above average rainfall in the region, including California. The jet stream shifts south leading to wetter and cooler conditions in the southern states and drier conditions in the Pacific Northwest.
The Neutral phase represents the averages for ocean temperatures, winds, surface pressure, and rainfall.
What Does La Niña Mean for Plants and Wildlife on The Preserve?
The amount of rainfall that we expect on the Preserve is based on the current ENSO phase. For the past few months, The Preserve has been experiencing Neutral conditions based on ENSO. However, the National Weather Service Climate Prediction Center recently issued a La Niña Watch with a 87% chance of La Niña conditions for the 2021-2022 winter. This means we should begin to expect less-than-average rainfall. Reduced rainfall will affect many of the natural resources throughout The Preserve and the Conservancy must plan accordingly.
Using last year’s La Niña as a reference, we have a pretty thorough understanding of how our plants, animals, and land management plans will be impacted. Last year, the Preserve was within the average rainfall amount at 26 inches, but the rain was late, producing late blooms and reducing water retention in the soil.
Some native wildlife species that depend on ponds and streams have the upper hand when it comes to dealing with variable rainfall year to year because they have adapted under these conditions. Many of our amphibian species, such as the California tiger salamander, have evolved with vernal pond systems that fill up in the winter and dry out in the summer. As the water gets low and warms up, California tiger salamanders and other native amphibians metamorphose more quickly so they are able to leave the ponds earlier. As invasive species like game fish and bullfrog have not adapted to these conditions, they die when the ponds dry up. Some of our species prefer ponds with vegetation while others like little to no vegetation; some prefer vernal ponds while others require perennial water. By ensuring we have all the varieties of pond types, we have enough niches to sustain wildlife through the La Niña phase.
Overall, there were less wildflowers throughout The Preserve compared to the El Niño years. The last El Niño led to the great wildflower showing of 2019. Many of the hillsides along Rancho San Carlos and around Black Mountain were blanketed with lupins and poppies. Last year, there were significantly fewer blooms in the same areas.
The erratic rainfall also stunted average vegetation growth. The lack of growth was most notable in annual grasses and species abundance. Last year, the wild oats were reaching hip height while in 2019 they grew taller than Dr. Rodrigo Sierra Corona, our Director of Ecological Management.
How Does La Niña Affect the Conservancy’s Land Management Planning?
So how will La Niña affect our land management planning? We will plan for a drought year. That said, we will have to wait to see what happens and adapt from there.
If we get low precipitation, there will be less forage available for wildlife and our cattle that work to restore the grasslands of The Preserve. Thus, we may have to reduce the herd size to prevent overgrazing and ensure the health of both the herd and the grasslands. We won’t know until around April or June, when we will be able to assess how much forage is available.
The weed management program will also have to adapt to the changing conditions. The French broom removal season will have a smaller window because the soil will dry up quicker and cement the roots in place, making it nearly impossible to yank out.
Yellow star thistle was a big problem this past year. It came back strong, even in areas where we’ve treated previously, so we had to change our schedule to ensure we were able to go after it all. Another weed that surprised us last year was mustard. In previous years the mustard population in our treatment areas was decreasing. However, the drier conditions suited the mustard, causing more to sprout at a greater density. This coming field season, we will schedule more time treating yellow star thistle and mustard based on last year’s experience.
Another effect of the late rainfall and low water retention was a decrease in thistle and poison hemlock populations, which was great because we were able to cover more ground eradicating those species than previous years. We anticipate that we will spend less time managing poison hemlock and other thistles during the La Niña phase since they prefer cool, wet winters.
Adapting is the Key to Success
Varying climate conditions such as La Niña and El Niño keep us land managers on our toes. We must adapt our plans to the changing conditions if we are to succeed in fulfilling our mission to protect, restore, and enhance the natural resources of the Santa Lucia Preserve. While we expect a warmer, drier winter influenced by the La Niña phase, we must also allow some wiggle room for any changes that might occur. Here’s to hoping for rain!