Torrential Rains Wipe Out California Monarch Butterfly Population

ON 03/07/2023 AT 08:25 AM

While the accumulated rain and snow of the last several weeks in California provided short-term respite from the regional drought, there was one victim which will take a long time to recover for the damage the storms brought with them.

Monarch Butterflies at Pismo State Beach

A string of Monarch Butterflies, shown here overwintering in 2015 in a photo taken at California's Pismo State Beach Monarch Preserve. Photo: Steve Corey, CC

As of the end of December 2022, California was suffering from an extreme drought. It had already decimated many plant, animal, fish, and insect populations just from the lack of water and heat alone.

A planning session was held then with the seven states who are members of the Colorado River Compact, the over 100-year-old agreement which regulates how the states of Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming, plus 30 Native American tribes and part of Mexico, divide up the increasingly precious and declining water resource available in the Colorado River and the man-made reservoirs of Lake Mead and Lake Powell. The goal of the session was to agree upon mandatory water allocation cutbacks of 20% or more from many of those states. It was a decision which will affect over 40 million people along with extensive agricultural properties, and a wide range of corporations. Those companies include conventional factories with lesser water needs, and others, such as semiconductor plants in Arizona, which use high quantities of water for their silicon chip fabrication processes.

The states present at that meeting failed to reach an agreement on the water allocation. The clock was ticking on a deadline after which the Department of the Interior might be forced to dictate cuts to all members.

Next, from late December through mid-January, an unusual triple-wave blast of “atmospheric rivers” carrying water from thousands of miles away in the Pacific Ocean into northern and central California partially refilled many of the regional lakes, rivers, streams, and man-made reservoirs in at least part of the state. The flooding was extreme, damage extensive, and those trapped in the floods and rains scrambled to find cover.

San Francisco set a record when it received five inches of rain in the single day of December 31, 2022. It was the wettest day ever in the 170-year history of record keeping for the city. Many other northern California areas recorded rainfall of up to 4 inches each during those first heavy rain events of the three-part atmospheric river deluge.

While damage was extensive to property and farmland, the heavy rainfall over those weeks brought with it what state water agency officials saw as positive news, that there was now considerably more water than just one month before. It may not have helped six of the seven states in the Colorado River Compact, but maybe California was a bit better off with respect to the crippling drought than a month earlier.

Then, over a period of two weeks covering the last full week of February and last week, a brutal California cold snap which extended as far south as San Diego, and carried with it more torrential rains, heavy snow, and some near-blizzard conditions extending into the mountains and east of Los Angeles. Mountain ranges in the San Bernardino area saw as much as two feet of snow accumulate there, just within days.

As of March 2, the snowpack had rendered many roads impassable, especially at higher elevations. Grocery stores ran out of food for many stuck there, gasoline supplies were exhausted for those with vehicles capable of traveling, and in the most badly hit regions an estimated 75,000 people remained without electrical power for days. Other areas had unstable power conditions which would shut off electricity often without warning.

Conditions were so severe that California Governor Newsom brought in the National Guard to provide immediate assistance in many areas. He also declared a state of emergency in the counties of Amador, Kern, Los Angeles, Madera, Mariposa, Mono, Nevada, San Bernardino, San Luis Obispo, Santa Barbara, Sierra, Sonoma, and Tulare. 

The rains have now mostly passed, roads have been cleared, and electrical power has been restored to most.

Just as when other disasters have hit, the next step was to begin to assess lingering damage. That is when researchers learned something catastrophic happened because of the December-January rains. They were also likely harmed even further by the cold and snowy winter storms that followed.

According to the conservation organization Xerces Society, which just completed its Western Monarch Butterfly counts which covered the period through the rains in January, the total number of that long-distance migrating species which is so important to pollination for a wide variety of plants dropped by 58% just in this season. It is also a potentially even more serious decline in the species will be discovered after the latest butterfly die-off — caused by the severe cold, heavy snows in the California mountains throughout state, and yet another bout of heavy rains along with them — are finally added up.

The measurements were made at 169 monitoring sites where the Monarch Butterfly typically spends its more dormant stage every year in California. In this year’s overwintering season, as it is called, in which the Monarchs cluster with others and consume little, two counts were made. One was towards the end of November 2022 and the other shortly after New Year’s Day.

The count is made throughout the year by partners of the Xerces Society and trained community volunteers. These most recent field estimates are used by scientists and agronomists to project how many Monarchs will be able to breed in the spring days ahead.

Graph showing decline of Monarch butterflies in California.

This graph shows the total monarchs reported and number of overwintering sites monitored for the Western Monarch New Year’s Count from Dec. 2016 to Jan. 2023. Graph: Xerces Society

The 58% decline in the counts showed a total of 116,758 of the species remaining, compared to the previous count. While the number is relatively high, mostly because the starting point was higher to begin with attribute more to luck than a trend, the researchers note the decline is far worse than the typical 35-49% average decline for the last six winters.

The Xerces report notes that Monarch totals fell at 119 of the 169 sites, increased in 14, and stayed roughly the same in 34 of the sites.

Where the butterflies choose to overwinter has a bearing on how weather conditions may affect their populations, of course. This latest report from Xerces notes that 49% of the butterflies counted were in San Luis Obispo County and 28% in Santa Barbara County, with just 11% in Monterey County and 10% in Santa Cruz County located more northwards. All these regions were strongly affected by the atmospheric rain waves of December and January. These habitats were also where the low temperatures, plus heavy snowfall and additional rains arrived in late February to the first days of March.

The seriousness of the current Monarch drop is even clearer from a long-term view. Millions of this species used to make the transit to the California cost during the 1980s and 1990s. Those numbers have fallen by over 90% since that time.

Researchers at Xerces said the storms impacted the butterflies by deaths where they were overwintering, from predators, and by flying away from the sites to save themselves. The increasing peril from the climate crisis and heavy pesticide use in the state were also cited as major contributors to their elimination.

Insect populations around the globe have collapsed due to climate change, chemical pollution and habitat loss, and this of course has a severe negative impact on eco-systems.