Drought to deluge? El Nino's impact on California

California's drought drama and how we got here
California's drought drama and how we got here   

As bad as California's drought has gotten, a strengthening El Nino season could mean help is on the way, bringing much needed showers to the Golden State. But El Nino may present its own problems.

A CNBC analysis of annual California rainfall over the past 60 years shows a significantly wetter rain season—averaging nearly five more inches of rain during moderate to very strong El Nino events. In fact, the six wettest years in California over the last half-century followed at least a moderate El Nino recording. ( Tweet This)

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The likelihood that the United States will in 2015 experience an El Nino that persists all the way through summer now stands at 90 percent, according to the Climate Prediction Center, part of the National Weather Service that focuses on El Nino forecasts. Meteorologists like Jan Null say there are no guarantees when it comes to weather modeling, but a strong El Nino event could be coming.

"The forecast models are becoming more and more robust, shifting from the weak category to the strong—some even pointing to a very strong El Nino season," he told CNBC.

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El Nino may already be manifesting itself now—the intense rains seen over the last month in Texas and Oklahoma are a phenomenon typically seen in past El Ninos. Texas, especially the Houston area, has been inundated with rains in the last week that have claimed at least 10 lives.

However, for reasons specific to California, El Nino can present its own challenges to the Golden State. Five extra inches of rain spread over a year can help ease drought concerns, but can have disastrous effects if it all falls in just a matter of weeks or even a few months.

First, California is not flat. It's more susceptible to landslides than places like Texas and Oklahoma.

In 1982, more than 30 people died when 18,000 landslides ripped through the San Francisco region, destroying more than 7,000 homes and businesses and causing nearly $1 billion in inflation-adjusted damage. Thousands more landslides rolled through the same region in 1998, causing $200 million in damage, according to some estimates.

Those two years were particularly strong events—the only ones in history to be categorized as "very strong," meaning they created ocean temperature that were at least 2 degrees centigrade above seasonal averages.

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Tim McCrink, supervising geologist at the California Geological Survey, said the connection between rainfall and landslides has repeated itself over time.

"The correlation between rainfall and landslides is pretty solid," he said. "They can be caused by earthquakes too, but you won't have landslides without the rainfall."

Second, wildfires exacerbate the threat presented by landslides, and California has entered wildfire season.

McCrink distinguished between the more dangerous, quick-striking landslides caused by debris flow in flash floods, and the slower moving, deep-seated landslides that develop over longer periods of rainfall.

The threat of rainfall-induced debris flows becomes even more dangerous after wildfires, to which much of California remains particularly susceptible—largely due to the drought.