El Niño's Hidden Hillside Threat: Why Homeowners Should Prepare for More Than Heavy Rain

Mercury explains how a strengthening El Niño could increase hillside hazards and why understanding property risks is an important part of winter storm prep.

LOS ANGELES, Nov. 5, 2026 /PRNewswire/ -- Mercury Insurance (NYSE/NYSE TX: MCY) is encouraging homeowners to look beyond traditional flood risks as a strengthening El Niño raises concerns about potentially damaging winter storms, particularly in hillside communities and areas recovering from wildfires. While heavy rainfall can threaten homes through flooding and water intrusion, saturated slopes, unstable terrain and fast-moving debris flows can create additional hazards that homeowners may not recognize until conditions become dangerous.

The National Oceanic and Atmospheric Administration (NOAA) reported in its October outlook that El Niño continues to strengthen, with a greater than 83% chance of strong-to-very strong conditions persisting through January-March 2027. Although El Niño can influence winter precipitation patterns across the United States, its effects vary by region, and individual storms cannot be predicted solely from the strength of the climate pattern.

"El Niño changes the larger atmospheric conditions that influence where storms develop and how precipitation is distributed, but it doesn't mean every community will experience unusually heavy rainfall," said Steve Bennett, Senior Director, Climate and Catastrophe Science at Mercury Insurance. "The concern for hillside communities is what happens when significant rainfall interacts with local terrain, soil conditions and areas where vegetation has been damaged or removed. Those factors can turn a rainstorm into a much more serious hazard."

Why Hillsides Can Become Dangerous During Heavy Rain

Rainfall affects hillsides differently depending on slope, soil composition, vegetation, drainage and previous land disturbances. Prolonged precipitation can saturate soil, increasing its weight and reducing its stability. On steep terrain, these conditions may contribute to landslides or other forms of ground movement.

Recently burned areas present an additional concern. Wildfires often remove vegetation that once helped to stabilize soil and absorb rainfall. The intense heat from fires can also create water-repellent soil conditions, forcing rainwater to run rapidly downhill rather than soaking into the ground.

According to the U.S. Geological Survey, post-wildfire debris flows can develop after short periods of intense rainfall, even when the ground was not previously saturated. These flows may carry mud, rocks, trees and other debris downhill at dangerous speeds, threatening properties located well beyond the original burn area.

"One of the most important things homeowners should understand is that the amount of rain isn't the only factor that determines risk," Bennett said. "A short burst of intense rainfall over a recently burned hillside may create dangerous conditions, while a longer period of rain can gradually weaken an already unstable slope. Remaining alert to local conditions and paying close attention to emergency warnings is essential when preparing for winter storms."

What Hillside Conditions Mean for Property Risk

For homeowners, hillside exposure is about more than whether a property sits directly on a steep slope. Homes below hillsides, near natural drainage channels or downstream from wildfire-damaged terrain may also face hazards.

These same characteristics can be relevant to property underwriting, where insurers evaluate multiple factors to understand a home's exposure to potential losses.

"Property risk isn't determined by a single characteristic," said Holly Sacks, Portfolio Underwriting and CAT Managementat Mercury Insurance. "Insurers may consider factors such as a home's location, surrounding terrain, construction characteristics and exposure to natural hazards. For homeowners, understanding those conditions can help identify vulnerabilities and determine where additional professional evaluation or mitigation may be appropriate."

While underwriting criteria vary by insurer, state and insurance product, several property characteristics may warrant closer attention:

• Slope and surrounding terrain: Steep or unstable hillsides may present different hazards than relatively level properties.
• Drainage patterns: Runoff from neighboring properties, roads or higher elevations may affect where water accumulates and how it moves.
• Previous wildfire activity: Burned vegetation and altered soil conditions can increase erosion and debris-flow potential.
• Retaining walls and slope modifications: Existing structures, grading and changes to natural drainage may warrant evaluation by qualified professionals.
• Previous ground movement or damage: A history of slope instability, erosion or drainage problems may indicate the need for further investigation.

Homeowners should not assume that completing a particular improvement will automatically change their insurance eligibility, premium or coverage. Underwriting decisions depend on applicable guidelines and individual property circumstances.

Five Steps Homeowners Can Take Before Winter Storms

1. Understand the terrain around your home. Identify nearby slopes, drainage channels and areas affected by recent wildfires. Local government hazard maps and U.S. Geological Survey resources may help homeowners better understand their property's exposure.
   
   
2. Inspect drainage and runoff conditions. Keep gutters, downspouts and accessible drainage systems clear of leaves and debris. Direct roof runoff appropriately and avoid making drainage changes that could send water toward unstable slopes or neighboring properties. Consult a qualified professional when significant drainage or grading work is needed.
   
   
3. Watch for changes in the landscape. New ground cracks, leaning trees, separating retaining walls, unusual seepage or changes in how water moves across a property may indicate developing instability. Homeowners who notice these conditions should seek professional guidance rather than attempt potentially dangerous repairs.
   
   
4. Prepare for evacuation before storms arrive. Residents near burn scars or identified debris-flow hazard areas should monitor National Weather Service forecasts and local emergency alerts, identify evacuation routes and prepare essential supplies. Debris flows can occur rapidly, and homeowners should follow evacuation instructions without delay. Sandbags and ordinary retaining walls cannot reliably stop a major debris flow.
   
   
5. Review insurance coverage before damage occurs. Standard homeowners insurance generally excludes flooding and many forms of earth movement. Separate flood insurance may cover certain qualifying mudflow losses, but landslides and other ground movement are typically treated differently. Homeowners should speak with their insurance agent about applicable exclusions, available coverage options and potential gaps.

Why Insurance Coverage Deserves a Closer Look

Mudflow, mudslide, debris flow and landslide are often used interchangeably in everyday conversation, but they can have different meanings under insurance policies.

Flood insurance through the National Flood Insurance Program may provide coverage for qualifying mudflow events, generally involving a flowing mixture of water and mud. Landslides and other earth movement are generally excluded. Standard homeowners policies also commonly exclude flood and earth movement losses.

However, coverage determinations depend on the specific cause of damage, policy language and applicable state law. In California, for example, certain losses involving mudslides or debris flows following wildfires may be covered when a covered peril is determined to be the efficient proximate cause of the damage.

"Homeowners should never assume that all storm-related damage is covered the same way," Sacks said. "Understanding what a policy covers, what it excludes and whether additional protection may be available is an important part of preparing for severe weather. It's much better to have those conversations before a storm than after a loss."

Preparation Begins Before the First Storm

Although the strength of El Niño may increase the likelihood of certain seasonal weather patterns, the greatest risks to individual properties often depend on local conditions.

For homeowners in hillside communities, especially those near recent wildfire burn areas, early preparation should include understanding the surrounding terrain, identifying potential drainage concerns, consulting qualified professionals when necessary and establishing a reliable evacuation plan.

"Weather is only part of the equation," Bennett said. "The condition of the land beneath and around a home can be just as important. Knowing how those factors interact gives homeowners a better opportunity to prepare before severe weather arrives."

For information about El Nino weather preparation, visit the Mercury Insurance Resource Center.

About Mercury Insurance

Mercury Insurance (NYSE/NYSE TX: MCY) is a multiple-line insurance carrier predominantly offering personal auto, homeowners, renters and commercial insurance through a network of independent agents in Arizona, California, Georgia, Illinois, Nevada, New Jersey, New York, Oklahoma, Texas and Virginia, as well as auto insurance in Florida. Mercury writes other lines of insurance in various states, including commercial, business owners and business auto, landlord, home-sharing, ride-hailing and mechanical protection insurance.

Since 1962, Mercury has provided customers with tremendous value for their insurance dollar by pairing ultra-competitive rates with excellent customer service, through more than 4,200 employees and a network of more than 6,340 independent agents in 11 states. Mercury has earned an "A" rating from A.M. Best, as well as "Best Auto Insurance Company" designations from Forbes and Insure.com. For more information visit www.MercuryInsurance.com or follow the company on LinkedIn, Instagram or Facebook.

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SOURCE Mercury Insurance