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While many people feel the winter of 2015-2016 was a bit of disappointment—a betrayal even, since we didn’t get a record-busting Godzilla like 1982-83 and 1997-98 — I’m not one of them. Remember back in your science classes when you learned that scientists are just as interested in being wrong as being right, or that a busted hypothesis was equally important as one substantiated? Well, we can learn a lot from this quirky El Niño. Some forecasts were right on the money while others were consistently wrong, and now, as El Niño’s unpredictable twin sister La Niña strengthens, it’s worth asking what lessons there are to take from the 2015-2016 winter.

El Niño: Beyond the Hype

Bay Nature goes beyond the headlines to explore what the strongest El Niño in recorded history might mean — or not — for Northern California. We’ll post new articles here throughout the fall and winter.

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A Brief Review of the Past Winter

First of all, here’s a reminder about what happened:

Central and Northern California received slightly above average rain and snowfall, while Southern California was abnormally dry.
This dry Southern California was notable because that part of the state often receives copious rainfall during El Niño events, particularly during those categorized “very strong,” as was the case for this past winter.
Even in Northern California, though, we did not receive the record-breaking 180-200% above average amounts of rain and snowfall that we did during the last two very strong episodes (1982-83 and 1997-1998). Instead our rainfall anomalies were modest, a bit more or less of 125%.
The highest anomalies, the Godzilla El Niño if you will, went north into Oregon and Washington. Here’s a map of the west showing rainfall seasonal rainfall anomalies through the end of April. Note not just the wetness in western Washington state but also the negative anomalies in southern California where NOAA 90-day precipitation outlook models forecast considerable wetness:

Which brings us to those 90-day outlooks (not forecasts, mind you). Here are two of them, one from early in the season, another from mid-winter. These 90-day outlooks dramatically missed the boat by showing high probabilities for an anomalously dry Pacific Northwest.

Why Did Both Theory and Computer Models Predict Rain in Southern California and A Dry Pacific Northwest?

Up until this year, the standard model for El Niño effects was that warm water off the coast of southern California energizes the sub-tropical branch of the Pacific jet stream, steering storms into the southern portions of North America, from southern California eastward across the Gulf States. With moisture-laden Pacific storms captured by the sub-tropical jet, the northern polar jet would run dry, which is why all the forecast models predicts drought for the Pacific Northwest. Also important to this conventional wisdom is the role of the Aleutian low pressure system. Its counter-clockwise rotation pumps warmer air from the sub-tropics northward, which explains the warm-and-dry forecast for the northern part of the continent.

What Really Happened

As we reported in January this year’s El Niño was taking on quirky traits, with the polar branch of Pacific jet remaining in firm control and steering most storms into the Pacific Northwest. This satellite image, for example, shows a well-defined atmospheric river providing the moisture tap for series of wet storms.

The image, however, does capture two important explanations for the unanticipated effects of this winter’s El Niño: a ridge of high pressure between Hawaii and the southern California coast that split the Pacific jet, and a weaker Aleutian low.

This splitting effect, which sent storms north instead of into southern California, is described in our January post (in which I also wrongly predicted the southern branch would strengthen in February and March). And the ridge of high pressure that either split the Pacific jet or actually redirected it northward could have been caused by increased winter-season strength of the Hadley Cell, an atmospheric circulation system better known for creating our summer-time Pacific High.

A Hadley Cell moves heated air from the equatorial zone upward, and then poleward, where it then descends, creating surface high pressure. The northern hemisphere Hadley Cell is most active in the summer season, when solar heating is greatest on our side of the Equator. Not only does this descending air create the Pacific High that is responsible for California’s dry summers, but it also drives the prevailing northwest winds that drive our offshore oceanic upwelling system.

What caused this unusual strengthening of the winter-season Hadley cell is unclear at this point (at least to me), but the implications could be huge if this feature becomes a permanent part of our West Coast climate system. Summers could become windier and perhaps foggier, autumns could become drier, and Southern California might see less and less winter-season rainfall. I don’t think this strengthening of the winter-season Hadley Cell is an inevitable product of global warming — at least right now.

The role of a weakened Aleutian low in producing the observed rainfall pattern is less clear, although I would opine that instead of pushing the polar jet northward as in a “typical” El Niño, it allowed that branch of the Pacific jet to stay on its southern fringe where it could actually enhance — rather than inhibit — storm development.

What Did We Learn from This Winter’s El Niño?

Most obvious is that all El Niño’s are not the same and the ENSO template for California must be revised. To reinforce that point I charted monthly rainfall figures in Oakland for this winter’s rainfall compared to that of the two most recent very strong El Niños. The intra-and inter-seasonal variability alone should have cautioned us about making Godzilla-like predictions:

Second, the media should try to avoid sensationalizing the possibility of extreme weather events before they happen. That’s particularly worth keeping in mind as we move from El Niño to a predicted strong La Niña, and front-page newspaper headlines are already declaring a continuation of the drought.

Finally, the public must keep pressure on our politicians to fund climate-change science. While I’m not sure many people suffered from the errors in this winter’s forecast (except maybe those in southern California with a surplus of sand bags in their front yards), the more we know about global warming and climate change, the better prepared we’ll be. California has the largest population living in, and the highest value economic system dependent on, the world’s most highly variable rainfall regime. NOAA has described El Niño as the best predictor we have of rainfall, and this year it didn’t work out as advertised. We’re all better off if we figure out why, and adjust our thinking. As the pundits like to say, “there’s no such thing as average rainfall in California: there’s either too much or too little.”

The Gulf of the Farallones National Marine Sanctuary, along with its sister sanctuaries to the north and south, Cordell Banks and Monterey Bay, are sentinels for the effects of global warming on ocean waters. And, as documented in a report released at an event at the California Academy of Sciences on June 3, Central California’s offshore waters and coastline are already showing the effects of global warming: warmer surface waters, higher sea level, stronger winds, more intense upwelling, increased acidification, and accelerated shoreline erosion. As a result, offshore ecosystems and food webs are being reshuffled as all organisms, from zooplankton to sperm whales, adapt (or don’t) to these new conditions.

The study was authored by a working group of marine scientists from California universities and resource agencies. (Download full report and executive summary.) Maria Brown, Farallones sanctuary superintendent, said because this study is the first to compile the effects of global warming on a national marine sanctuary, it will become a model for similar work at other national sanctuaries. William Douros, regional director for the National Oceanic and Atmospheric Administration, which has jurisdiction over marine sanctuaries, said he hopes to see new climate change studies that link together all five West Coast sanctuaries, from the Olympic Coast in the north to the Channel Islands in the south, to provide full context for the climate change effects on the California Current ecosystem.

In the panel discussion at the California Academy of Science that accompanied the release of the report, UC Davis researcher John Largier, chair of the science working group, emphasized that although the study identifies and synthesizes climate change impacts for the two sanctuaries, it does not predict future changes. Instead, it provides a foundation of scientific insight to enable staff at each of the two sanctuaries to develop and prioritize more detailed strategies for monitoring the effects of climate change. Later, with more specific and localized information in hand, the sanctuaries can then develop appropriate resource management plans.

: The new report focuses on the impacts of ecosystems at Cordell Bank and the Gulf of the Farallones, both highly influenced by the California Current. Click map for larger version. Map courtesy NOAA.

The report states that the most severe ecological disruption will be associated with changes in upwelling, ocean temperature, sea level rise, and ocean pH (acidification). Currently, upwelling appears to be increasing along the north-central California coast due to the more rapid increase in land temperatures contrasted with those of the ocean, creating atmospheric pressure gradients that produce stronger northerly winds, which, in turn, drive coastal upwelling. Given that the California Current ecosystem is characterized by upwelling-dependent food webs, the impact of any change in the intensity of upwelling will effect its nutrient delivery system and subsequently resonate through the whole coastal ecosystem. For example, more intense upwelling produces stronger eddies that then carry the larvae of fish and other organisms farther west out to sea, disconnecting populations and disrupting their developmental timing, leading to higher mortality. This unusual larval transport may explain the low number forage fish (rockfish, anchovies, and sardines) responsible for the high chick mortality among some kinds of seabirds in 2009.

In contrast to cooler waters in the upwelling area, surface waters farther offshore are warming as the ocean absorbs heat and carbon dioxide from the atmosphere. The shallow waters of coastal bays and estuaries such as Tomales and San Francisco bays have also warmed, resulting in steep temperature gradients from east to west. While spatial and vertical patchiness has always been a characteristic of the California Current ecosystem, these new extremes may be causing the change now being documented offshore.

Warmer surface waters also inhibit the vertical mixing of ocean waters that is the foundation of nutrient production. Without vertical mixing, nutrient-rich cold waters can produce blooms of zooplankton that absorb nutrients and create zones of low dissolved oxygen, which can both kill off certain native species and invite in species that thrive in low-oxygen conditions. This probably explains the recent invasion of the Humboldt squid, a voracious subtropical predator that is now disrupting local ecosystems. Bill Sydeman, an ecologist with the Farallon Institute and member of the science working group, calls the squid an invasive species on par with scotch broom, pampas grass, and other well-known terrestrial weeds because of its rapid spread and the havoc it’s causing to endemic ecosystems.

: Ochre seastars might expand their range due to changing conditions. Photo by Kibuyu, used under Creative Commons.

Warming ocean waters also account for most of the eight-inch rise in sea level measured at the San Francisco tidal gauge over the last 100 years because of thermal expansion. Not only has this sea-level rise accelerated shoreline erosion, but it has also changed intertidal communities as tidepool fish, crabs, and other shellfish relocate along rocky shores. Some species apparently find this reshuffling to their advantage; the ochre seastar, for example, is expanding its range at the expense of the slow-moving California mussel. Higher sea levels are also reducing accessibility to traditional haul out and nursery areas for pinnepeds (seals and sea lions). While the agile California sea lion can scramble to higher ground, harbor seals may suffer adverse effects because they have such restricted mobility out of the water.

Finally, ocean waters continue to become more acidic as they absorb more and more carbon dioxide. This issue, which has been called “the other CO2 problem” because of its severe threat to marine life, may seriously alter marine ecosystems by preventing organisms from forming calcium carbonate structures, like shells and exoskeletons (obviously critical for hundreds of species, from coral to crabs). Because deep waters are more acidic than those on the surface, the report warns, the California coastal region may suffer double jeopardy: More intense upwelling could bring deep, highly acidic water forming a surface layer that’s uninhabitable for many key invertebrate plankton populations that form the basis of the California Current food web, fueling everything from tidepool anemones to blue whales.