heavy rains

La Niña has arrived

February 26, 2025 By EarthWise Leave a Comment

After seven months of waiting following the end of the recent El Niño condition, La Niña finally showed up in the eastern Pacific Ocean in early December.

El Niño and La Niña are climate patterns in the Pacific Ocean that can affect weather worldwide. Normally, trade winds in the Pacific blow west along the equator, taking warm water from South America towards Asia. To replace the warm water, cold water rises from the depths. During El Niño, trade winds weaken and warm water is pushed back east, toward the west coast of the Americas. As a result, areas in the northern U.S. and Canada are dryer and warmer than usual.

During La Niña, trade winds are stronger than usual, pushing more warm water toward Asia. This results in more upwelling of cooler water from the depths. This tends to lead to drought in the southern U.S. and heavy rains and flooding in the Pacific Northwest and Canada. During a La Niña year, winter temperatures are warmer than normal in the South and cooler than normal in the North.

According to the report published in January by NOAA, the La Niña that has arrived is not a particularly strong one. Sea surface temperatures are only about 1.3 degrees Fahrenheit below average in the tropical Pacific. The report also suggests that the La Niña condition may not stick around very long.

The El Niño-Southern Oscillation phenomenon adds a natural source of year-to-year variability in global temperatures. The presence of La Niña for at least part of this year may temporarily keep the lid on rapidly climbing global temperatures.

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La Niña Is Here

Photo, posted November 23, 2011, courtesy of NASA Goddard Space Flight Center via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

California: Drought Or No Drought? | Earth Wise

April 26, 2023 By EarthWise Leave a Comment

Just a few months ago, millions of people in California were living under challenging water conservation rules. The past three years were the driest on record and reservoirs were depleted, landscapes dried up, and the snowpack in the Sierras at very low levels.

But in recent months, a dozen atmospheric river storms have brought huge amounts of rain and snow to the state. Twelve out of 17 major reservoirs in the state have been replenished, the snowpack is over 240% of normal, and brown hills are blooming once again.

So, is the California drought over? According to the experts, the answer is: sort of.

The record snowpack and heavy rains have erased the most severe aspects of the drought in many parts of the state. Only 9% of the state is now experiencing “severe” or “exceptional” drought, down from 55% last fall.

But the changes are basically all at the surface. Groundwater in the state is still extremely low and the state’s cities and farms are still using more of it than is appropriate. The state has been unwisely overusing its groundwater aquifers because of the drought and this one year of heavy rains cannot replenish levels that have been dropping for years.

California has been rolling back many of the most severe drought restrictions that had been imposed but has not entirely lifted the drought emergency status. Meanwhile, the massive snowpack in the mountains will begin to melt as the weather warms and, in many areas, Californians will face flooding. Water is a complicated business in California.

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Drought or no drought? California left pondering after record winter deluge

Photo, posted August 28, 2019, courtesy of Joyce Cory via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

California Flooding | Earth Wise

February 2, 2023 By EarthWise Leave a Comment

Starting in December, a series of “atmospheric rivers” brought record storms to California producing as much rain in three weeks in some areas as they normally have in an entire year. The historic levels of rain (and snow in the mountains) have swollen rivers, flooded roads and homes, forced evacuations, knocked out electric power for millions of people, and resulted in more than 20 deaths.

Atmospheric rivers are air currents that carry large amounts of water vapor through the sky. They are not unusual for California but recurrent waves of them like those that have happened recently are very infrequent. Studies by the U.S. Geological Survey have shown that such a phenomenon recurs in California every 250 years. There were a series of storms causing disastrous floods in California in 1861-62.

The atmospheric rivers are born in the warm waters of the tropical Pacific. During La Nina phases, the atmospheric rivers typically make landfall on the northern West Coast. During El Nino phases, atmospheric rivers are more likely to end up in Southern and Central California. During transitions between the phases, as is happening now, the storms can cover large parts of the state.

Modern forecasting is pretty good at predicting the forthcoming occurrence of these storms and has led to some helpful actions, such as reservoir operators preventing dams from overflowing or bursting. But there is a gap between science and decision-making. It is pretty clear what needs to be done when tornados or hurricanes are on the way. It is less clear what actions are appropriate when there are going to be repeated heavy rainstorms.

These storms will have an effect on California’s megadrought, but just how much of an effect remains to be seen.

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Flooding in California: What Went Wrong, and What Comes Next

Photo, posted January 5, 2023, courtesy of Sarah Stierch via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio