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Krakatau's effects in southern California

In 1884, the year after the eruption of Krakatau, summer temperatures in the northern hemisphere fell 1.2oC below average. Krakatau’s influence was seen and felt around the globe in vivid sunsets and stormy weather. Southern California experienced a year of record rainfall. Typical temperature and weather patterns did not recover for years. For the saguaro (Carnegiea gigantea), the perturbations appear to have been 'just right' for new growth.
A species of the arid southwestern United States, the saguaro is sturdy in maturity but delicate in the early years of its life. Though mature individuals can top 12 meters, new cacti grow only a few millimeters in the first year. Young saguaros are susceptible to heat and cold, vulnerable to drying out or freezing in the extremes of their desert environment. For a critical two to three years, until they grow large enough to withstand cold and drought, they demand cool summers, mild winters and sufficient rain: a combination of weather conditions abnormal for the Sonoran desert.

Research found that many of the large exemplars of the famous cacti in the Southwest today started their lives in the shadow of the 1883 eruption. Biogeographer Taly Drezner believes that distant volcanic eruptions and the emergence large numbers of saguaros are connected.
[Anak Krakatau - The Child of Krakatau]

“The saguaro is key to the survival of many species. Almost every animal in the Sonoran uses them in some way, as a nest site, or food, or a cool refuge,” said Drezner, a professor at York University in Ontario. Temperatures can easily exceed 40oC every day for weeks in summer, when saguaro seedlings have just germinated.

“I started noticing that these saguaro age cohorts followed notable volcanic eruptions,” said Drezner. “I knew that volcanoes drive milder summers and winters, and typically more rainfall for an extended period–two to three years after the event, which is a perfect window of time for the saguaro to get established and have a chance to survive.”

Saguaro boom years tracked the peaks in the dust index, particularly in the marginal environments. High volcanic dust levels also correlated with warmer, wetter, local winters and more rain in late spring.

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