Since 1990, domestic migration to California has flipped to a deficit. In the last two decades, the state lost nearly 3.4 million residents through migration to other states. In other words, it lost about four-fifths of what it had gained through domestic migration in the previous 30 years. Foreign immigration filled the gap only partially. Inflows from overseas peaked at 291,191 in 2002 and sank to just 164,445 in 2011. Meanwhile, net domestic out-migration has averaged 225,000 a year over the past ten years.
In 2005, foreign immigration ceased to make up for the drop in domestic migration to California. Since that year, California’s annual net migration has been negative—more people leave the state than come to live in it. Natural increase in the resident population—births minus deaths—cushions the blow of this out-migration, but that, too, is falling. It peaked at 397,000 in 1992 and had dropped to 271,000 by 2011.
Part of the migration out of California is related to the aging population. The biggest gaining state was Florida which is a popular retirement destination.
California had a higher unemployment levels than the US average.
California had become a more crowded state and the infrastructure did not keep up and homes prices went up.
Another Study forecasts less robust population growth in California to 2050
There is USC study of Calfornia's population that is more pessimistic about population growth than the State forecasts. They are projecting about 3.5 million instead of 5 million growth per decade.
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