El Niño Tree Preparation & Storm Damage Prevention in Sonoma County

El Niño is not simply a phrase used to describe a rainy winter. It is a large-scale ocean-atmosphere climate pattern that begins in the tropical Pacific Ocean and can influence weather patterns around the world.

For the 2026–2027 season, El Niño deserves particular attention.

On September 10, 2026, NOAA's Climate Prediction Center reported that El Niño was strengthening and placed the probability of a very strong El Niño during the Northern Hemisphere fall and winter above 90%. NOAA also reported a 75% chance during the October–December period that the event could reach a threshold exceeding previous El Niño events in the modern record. NOAA emphasizes that even a very strong El Niño does not guarantee any particular storm or local impact, but stronger events can increase the likelihood of weather patterns historically associated with El Niño.

On September 21, 2026, California announced additional statewide preparedness measures in anticipation of the developing El Niño season, citing potential impacts including heavy rain, strong winds, flooding, landslides, debris flows, coastal impacts and infrastructure disruption.

That does not mean every part of Sonoma County will experience extreme rainfall, or that every storm will be severe.

It means this is an appropriate time to prepare.

For trees, preparation matters because tree failures often occur when several conditions develop simultaneously: wet soil, prolonged precipitation, strong winds, weakened root systems, heavy canopies, hidden decay, previous construction damage, poor branch attachment or existing structural defects.

Those problems are much easier to evaluate on a calm September or October afternoon than during a winter windstorm at midnight.

El Niño is part of a naturally occurring climate cycle known as the El Niño-Southern Oscillation, commonly abbreviated ENSO.

During El Niño, portions of the tropical Pacific Ocean become warmer than average. Those ocean-temperature changes interact with the atmosphere and influence large-scale circulation patterns, including the position and behavior of the jet stream.

The result can be major changes in precipitation, temperature, storm tracks and weather patterns across different parts of the world.

California's experience during El Niño is complicated.

An El Niño winter does not automatically equal a wet winter everywhere in California. Northern California's relationship with El Niño is less consistent than Southern California's, and individual storms remain impossible to predict months in advance.

However, significant El Niño events can contribute to conditions favorable for powerful Pacific storm systems. During active winter patterns, Northern California can experience atmospheric rivers, repeated rainfall, high winds and saturated soils.

Those conditions matter greatly when evaluating trees.

A mature tree is an enormous living structure interacting continuously with soil, wind and gravity.

Under ordinary conditions, a healthy tree can tolerate surprisingly powerful forces. Trees move in the wind. Branches flex. Trunks bend. Root systems distribute loads through the soil.

Problems can develop when the forces acting on a tree exceed the capacity of the tree or soil to support them.

During an El Niño winter, the combination of prolonged precipitation and wind can reveal structural weaknesses that may have gone unnoticed during dry weather.

Consider a large tree with a dense crown, several extended lateral limbs and a compromised root system.

On a calm summer day, nothing may appear unusual.

Now add several days of rainfall.

The soil becomes increasingly saturated.

Then a strong Pacific storm arrives with powerful gusts.

The crown catches wind like a large irregular sail. Forces travel through the branches, into the trunk, through the root flare and into the structural roots supporting the tree.

If the soil has lost some of its ability to resist movement, or if roots are damaged or decayed, the entire root plate can begin moving.

That is one reason trees sometimes uproot during winter storms even though they appeared green and healthy only days earlier.

Wind does not affect every tree equally.

A dense canopy presents more surface area to wind than an open canopy, but that does not mean every tree should be aggressively thinned before winter.

Excessive pruning can create new problems.

Removing too much foliage can reduce the tree's ability to produce energy, encourage vigorous sprouting, alter branch loading, expose previously protected branches to wind and sun, and create long-term structural issues.

Proper storm preparation is not about stripping a tree.

The objective is to address identifiable defects while maintaining a healthy, functional crown.

Depending on the tree, that may involve removing dead branches, reducing selected heavy or overextended limbs, correcting previous poor pruning where possible, improving building clearance or reducing specific branches with elevated failure potential.

Every pruning cut should have a reason.

When property owners become worried about storms, one common reaction is to ask for a tree to be dramatically shortened.

This is often described as topping.

Topping generally involves removing major portions of a tree's crown by cutting branches or leaders back to arbitrary points rather than appropriate lateral branches.

For most mature trees, topping is not an appropriate storm-preparation strategy.

Large heading cuts can create extensive wounds. The tree may respond by producing numerous vigorous sprouts near the cuts. These shoots can grow rapidly but may have weaker attachment than naturally developed branches.

Over time, a topped tree can develop a dense crown of sprouts growing from compromised pruning locations.

Rather than permanently solving a structural problem, topping may create a cycle of repeated maintenance and future structural concerns.

Canopy Arborists evaluates trees individually and recommends pruning based on tree structure, species, condition, targets and objectives rather than simply removing a percentage of the canopy.

Not every tree requires pruning.

Sometimes the best recommendation is to leave a healthy tree alone.

However, certain observations justify a closer inspection, especially when the tree could strike a home, driveway, road, neighboring property, utility area, playground, parking space or heavily used portion of the property.

Important warning conditions can include:

dead or hanging branches; large broken limbs; cracks extending through branches or trunks; cavities; decay; fungal fruiting bodies around the trunk or root flare; significant lean that appears recent or has increased; soil lifting around the root plate; visible root damage; trenching or excavation near the tree; girdling roots; codominant stems with included bark; large branches with excessive end weight; old topping wounds; previous major branch failures; lightning damage; declining canopy density; substantial deadwood; compromised root flares; trees growing on unstable slopes; trees leaning toward valuable targets; and trees that have recently changed after nearby construction, grading or landscape modifications.

One of these observations does not automatically mean a tree is dangerous or must be removed.

It means the condition deserves professional evaluation.

Some trees develop two or more major upright stems originating from approximately the same point.

These are often called codominant stems.

Codominant structure is not automatically defective.

However, certain unions can develop included bark, where bark becomes trapped between expanding stems rather than forming a strong wood connection.

As the stems increase in diameter, the union may become increasingly stressed.

Large codominant unions deserve particular attention when there are cracks, previous failures, cavities, decay, excessive movement or substantial targets nearby.

Management options vary.

Depending on the situation, an arborist may recommend selective reduction pruning, periodic monitoring, supplemental support systems such as cabling, or removal when the defect and potential consequences are sufficiently significant.

The objective is not to make every tree perfectly symmetrical.

The objective is to understand its structure and manage unacceptable risk.

Branches naturally grow toward available light.

In landscapes, this can result in long lateral branches extending over homes, garages, fences, pools, patios or neighboring properties.

Long branches can develop considerable leverage.

This does not mean they should automatically be removed.

Appropriate reduction pruning can sometimes shorten selected branches and redistribute loading while preserving much of the branch and canopy.

This differs from making a large removal cut at the trunk or simply cutting the branch halfway back.

Reduction pruning should generally terminate at an appropriate lateral branch capable of assuming the terminal role.

Strategic pruning can provide meaningful structural improvement with considerably less impact on the tree than aggressive canopy removal.

The pruning history of a tree matters.

A tree that was heavily topped ten years ago may now have multiple large stems growing from old topping cuts.

From the ground, the canopy may look full and healthy.

A closer inspection may reveal large-diameter shoots attached around old decayed heading wounds.

Those areas deserve evaluation before major storm seasons.

Similarly, repeated lion-tailing — the practice of removing interior foliage and leaving foliage concentrated at branch ends — can alter loading and branch behavior.

Storm preparation sometimes requires correcting previous pruning gradually rather than trying to fix everything in one visit.

Trees are living systems.

Good arboriculture often involves long-term management.

Many Sonoma County properties are located on slopes.

Hillside trees require careful evaluation because the tree, root system, drainage patterns and surrounding soil all interact.

Water moving through a slope can affect soil conditions differently from water on level ground.

Previous grading, retaining walls, erosion, landslides, root cutting and drainage modifications can also influence stability.

Large trees above homes or neighboring properties deserve particular attention.

If a tree fails downhill, gravity and slope may increase the consequences.

Trees growing uphill from structures should therefore be evaluated not simply based on whether they appear alive, but according to their condition, structural features, root environment, slope and potential targets.

El Niño and atmospheric rivers are different phenomena.

An atmospheric river is a concentrated corridor of atmospheric moisture capable of transporting tremendous amounts of water vapor.

When atmospheric rivers reach California, terrain can enhance rainfall as moist air rises over coastal mountains.

The North Bay has experienced significant atmospheric-river impacts in previous seasons. During a major November 2024 event, the National Weather Service documented rapid rainfall accumulation, flooding in the North Bay, flood warnings on the Russian River, urban flooding and strong winds.

An El Niño pattern does not mean every atmospheric river will hit Sonoma County, nor does El Niño directly cause every atmospheric river.

For property owners, however, the practical concern is straightforward.

Periods of intense rainfall can saturate soils.

Multiple storms arriving close together can prevent soils from adequately draining between systems.

If powerful winds arrive during that period, tree loads can increase at the same time soil conditions become less favorable.

That combination deserves respect.

The best storm work is often performed before the storm is visible on a seven-day forecast.

When a major storm is only two days away, tree companies can quickly become overwhelmed with emergency calls.

Equipment, crews and scheduling capacity become limited.

Inspection before storm season gives property owners more choices.

A qualified arborist can examine the trees, identify priority work and separate urgent conditions from maintenance that can safely wait.

A practical El Niño tree-preparation checklist includes:

• Walk around your property and look upward as well as at the base of trees.
• Look for recently broken branches, hanging limbs and significant deadwood.
• Check trunks for cracks, cavities, decay and fungal growth.
• Look at major branch unions for separation or unusual movement.
• Look around the root flare for cracking soil, lifting roots or new movement.
• Consider whether construction, trenching or grading has occurred near trees.
• Identify trees capable of striking homes, bedrooms, vehicles, driveways, roads or neighboring property.
• Have higher-consequence trees professionally inspected.
• Complete necessary pruning before severe weather arrives whenever practical.
• Avoid unnecessary topping or aggressive canopy stripping.
• Check drainage around tree root zones.
• Avoid intentionally flooding or overwatering already saturated soil.
• Keep gutters, drains and drainage pathways clear.
• Know where your emergency shutoffs are located.
• Move vehicles away from obviously compromised trees when severe winds are forecast.
• Never attempt to remove storm-damaged limbs that are contacting electrical conductors.
• Stay away from fallen electrical lines and treat every downed line as energized.
• During storms, prioritize people and personal safety over property.
• Sign up for local emergency notifications and know your evacuation zone.

Sonoma County Emergency Management recommends preparing for flooding before storms, maintaining emergency supplies, planning evacuation routes, clearing gutters and drains and signing up for local emergency alerts.

In arboriculture, a target is a person, property or activity that could potentially be affected by tree or branch failure.

Examples can include homes, garages, vehicles, sidewalks, playgrounds, streets, neighboring structures, outdoor seating areas and frequently occupied spaces.

Targets are important because risk is not determined by tree condition alone.

Imagine two identical dead branches.

One hangs above a remote portion of a rural property that nobody uses.

The other hangs directly over the entrance to an apartment building.

The branches may have the same probability of failure.

The consequences are very different.

A professional tree-risk evaluation considers that difference.

Not necessarily.

One of the worst reactions to an El Niño forecast would be the unnecessary removal of healthy mature trees simply because storms are possible.

Trees are valuable assets.

A large mature tree cannot quickly be replaced.

Removal should be recommended when the condition of the tree, likelihood of failure, target, consequences and available mitigation options support that decision.

Sometimes pruning can reduce the concern.

Sometimes cabling may be appropriate.

Sometimes changing the target can reduce risk.

Sometimes periodic monitoring is reasonable.

And sometimes removal truly is the appropriate recommendation.

The purpose of an arborist inspection is to determine which situation applies.

Tree removal may become appropriate when structural defects or health conditions create a level of risk that cannot reasonably be reduced to an acceptable level through other management options.

Examples may include severe trunk decay, major root decay, catastrophic structural cracks, extreme instability, significant root loss, advanced decline combined with structural weakness or previous failures indicating substantial structural compromise.

Tree location also matters.

A severely compromised tree positioned directly above an occupied home presents different consequences from the same tree in a remote open space.

When removal is recommended, Canopy Arborists can explain the observable conditions behind the recommendation and discuss the practical options available.