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The Force of El Niño

Landslides, Flooding, Marine Life Impacted
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California and water have a love-hate relationship. While water is needed for the state to thrive, El Niño storms this winter are likely to bring major environmental hazards such as floods, landslides and coastal erosion, according to Cal State Fullerton researchers.

“We need to be ready. If the storm size will be as large as predicted, this year’s storms may trigger more mudslides and landslides than ever before,” said Binod Tiwari, professor of civil and environmental engineering. “It’s a natural phenomenon, which cannot be stopped, but we need to be prepared to protect our infrastructure, properties and lives.”

Southern California had unusually high rainfall due to El Niños in 1982-83 and 1997-98, and last year’s storms triggered many debris flows and mudslides, all resulting in significant rainfall-induced damages, said Tiwari, a globally known landslide expert.

Since the El Niño effect typically produces a series of rainfall events, this could impact the stormwater drainage infrastructure, which is not designed for such extreme storm events, resulting in severe flooding, added Phoolendra K. Mishra, assistant professor of civil and environmental engineering.

“The effects are expected to be more pronounced in urban areas,” said Mishra. “This may result in economic losses, as well as long-lasting social and environmental impacts.”

Both Tiwari and Mishra conduct research with students related to mitigating the impacts of natural disasters. Tiwari conducted a study with students last year through the Geotechnical Extreme Event Reconnaissance, supported by the National Science Foundation. The research focused on weather patterns and damages made by the debris flows triggered by the December 2014 rainfall.

Currently, Tiwari’s students are involved in simulations on the amount and duration of rainfall required in different types of soils that trigger landslides in Southern California.

“This winter’s predicted storms will have a direct effect to my current research,” Tiwari said. “We’ll be able to verify the results we obtained through our laboratory simulations with the actual impacts of the storms, which ultimately will enhance our capability to minimize landslide hazards.”

Mishra and his students are developing mathematical and laboratory models to better understand and quantify soil infiltration under dry, drought-like conditions.

“Once rain falls onto the ground, a certain amount of the rainwater infiltrates the soil. Rainfall in excess of infiltration capacity of the soil moves as runoff,” said Mishra, a hydrologist who studies groundwater flow and transport. “This infiltration rate depends on a variety of soil and storm conditions, such as soil composition and soil cover, as well as how hard it rains and how long the storm lasts.”

The state’s severe drought conditions may have considerably reduced the infiltration capacity of soil, which may lead to flooding in low-lying areas, landslides and ocean pollution during El Niño storms, Mishra added.

Heavy storms also can cause storm surges, larger surf and higher tides, said Joe Carlin, assistant professor of geological sciences. These could result in coastal, beach and cliff erosion in Orange County and throughout the region.

Carlin, an expert in marine geology, is interested in how coastal environments change or respond to extreme events, such as El Niño. Such events can have significant impacts to marine life.

“Understanding how beaches or marshes may be impacted by coastal erosion, and how they recover to these extreme events may give a better insight on how to manage these ecosystems over the next several decades as we prepare for increased sea level rise too,” he said.

The warmer ocean waters also can have significant impacts to marine life.

“We have already seen — and may see more — species negatively impacted as they may not be able to function in the warmer waters,” said Carlin, adding that the small red crabs that washed ashore locally this summer are related to the dramatically warmer waters. Other atypical species observed have been whale sharks, hammerhead sharks, green sea turtles and sea snakes.

“Increased rainfall driven by El Niño also can cause increased runoff to the ocean, which can transport pollutants that are harmful to marine life, and also increased nutrients that can lead to algal blooms, which can sometimes be toxic to some marine life.”

What do CSUF scientists anticipate from El Niño? See related story.