Plan on increasingly hot summers in LA

topic posted Wed, October 1, 2008 - 1:28 AM by  Unsubscribed
Cool Summer, Warm Future: Extreme Heat Days Increase For Southern California

ScienceDaily (Sep. 29, 2008) — Summer 2008 in Southern California goes down in the books as cooler than normal. The thermometer in downtown Los Angeles topped 90 degrees Fahrenheit (32.2 degrees Celsius) just once in July, August and the first two-thirds of September. But don't expect this summer's respite from the usual blistering heat to continue in the years to come, cautions a group of NASA and university scientists: The long-term forecast calls for increased numbers of scorching days and longer, more frequent heat waves.

One hundred years of daily temperature data in Los Angeles were analyzed by scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif.; the University of California, Berkeley; and California State University, Los Angeles. They found that the number of extreme heat days (above 90 degrees Fahrenheit or 32.2 degrees Celsius in downtown Los Angeles) has increased sharply over the past century. A century ago, the region averaged about two such days a year; today the average is more than 25. In addition, the duration of heat waves (two or more extreme heat days in a row) has also soared, from two-day events a century ago to one- to two-week events today.

"We found an astonishing trend – a dramatic increase in the number of heat waves per year," says Arbi Tamrazian, lead author of the study, and a senior at the University of California, Berkeley.

Tamrazian and his colleagues analyzed data from Pierce College in Woodland Hills, Calif., and the Los Angeles Department of Water and Power in downtown Los Angeles. They tracked the number of extreme heat days and heat waves from 1906 to 2006. The team found that the average annual maximum daytime temperature in Los Angeles has risen by 5 degrees Fahrenheit (2.8 degrees Celsius) over the past century, and the minimum nighttime temperature has increased nearly as much. They also found that heat waves lasting six or more days have been occurring regularly since the 1970s. More recently, two-week heat waves have become more common.

The team forecasts that in coming decades, we can expect 10- to 14-day heat waves to become the norm. And because these will be hotter heat waves, they will be more threatening to public health.

"The bottom line is that we're definitely going to be living in a warmer Southern California," says study co-author Bill Patzert, a JPL climatologist and oceanographer. "Summers as we now know them are likely to begin in May and continue into the fall. What we call 'scorcher' days today will be normal tomorrow. Our snow pack will be less, our fire seasons will be longer, and unhealthy air alerts will be a summer staple.

"We'll still get the occasional cool year like this year," Patzert continued, "but the trend is still towards more extreme heat days and longer heat waves."

So what's behind this long-term warming trend? Patzert says global warming due to increasing greenhouse gases is responsible for some of the overall heating observed in Los Angeles and the rest of California. Most of the increase in heat days and length of heat waves, however, is due to a phenomenon called the "urban heat island effect."

Heat island-induced heat waves are a growing concern for urban and suburban dwellers worldwide. According to the U.S. Environmental Protection Agency, studies around the world have shown that this effect makes urban areas from 2 to 10 degrees Fahrenheit (1 to 6 degrees Celsius) warmer than their surrounding rural areas. Patzert says this effect is steadily warming Southern California, though more modestly than some larger urban areas around the world.

"Dramatic urbanization has resulted in an extreme makeover for Southern California, with more homes, lawns, shopping centers, traffic, freeways and agriculture, all absorbing and retaining solar radiation, making our megalopolis warmer,” Patzert said.

These trends may capture the attention of utility companies and public health officials. "We'll be using more power and water to stay cool," says study co-author Steve LaDochy of California State University, Los Angeles. "Extreme heat, both day and night, will become more and more dangerous, even deadly."

The findings are published in the July 2008 issue of the Yearbook of the Association of Pacific Coast Geographers. JPL oceanographer and climate scientist Josh Willis was also a co-author on the research.

To learn more about NASA's Earth science missions, visit the Global Climate Change website at
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  • Re: Plan on increasingly hot summers in LA

    Mon, October 27, 2008 - 8:12 PM
    October shaping up as L.A.'s lost summer

    With eight days over 90, this could be the hottest October since 1965, forecasters say.

    Summer turned out to be a cooler than normal dud this year.

    But October dressed up as summer this Halloween season.

    With eight scorchers over 90 degrees this month, Los Angeles has been in the midst of the second-hottest October since 1877, according to climate records.

    "It's the summer we never had," said William Patzert, a climatologist for the Jet Propulsion Laboratory in La Canada Flintridge.

    The average daytime temperature in downtown Los Angeles this month has been 84.3 degrees, he said. The warmest October to date was in 1965, when the average daytime temperature was 84.5 degrees. September's average high temperature was 83.2 degrees, according to the National Weather Service.

    "In September we only had two days over 90," Patzert said.

    The warmest October in Los Angeles' recorded history -- an average of 84.5 degrees -- was 1965, when Southern California was blasted by hot, dry Santa Ana winds. On Oct. 23 of that year, Los Angeles had a temperature of 100 degrees. In San Diego, firefighters were busy battling three blazes amid the October heat wave.

    This October has also seen its share of wind-whipped brush fires, notably two huge blazes that burned dozens of homes in the San Fernando Valley.

    The reason for the high temperatures is fairly predictable. Several high- pressure systems parked over the Southwest have compressed and heated the air cycling into the region. The resulting Santa Ana winds have not been powerful so far, but they have arrived early and with regularity, Patzert said.

    "Every fall there's a great race. Will the Santa Anas precede the rains or vice versa?" he said. "So far the Santa Anas are ahead of the rains by at least five lengths."

    There's a chance this month may fall to third place after October 1999, when the average daytime maximum temperature was 84.1. The reason is that temperatures may drop just enough in the last four days of October, said Stuart Seto, a weather specialist for the National Weather Service in Oxnard. But maybe not, he said.

    "We may tie 1999," Seto said.

    At first, it looked like showers were on the way, but Seto said it looks as if the chances of rain this weekend are practically nonexistent. And that's bad, climatologists say, because Southern California has been so dry for so long and the conditions are ripe for wildfires.

    "We've had essentially eight months of no rain, and we're having one of the driest falls," Patzert said. "Either we're getting our quota of Santa Anas out early or this is a preview of coming attractions, which is scary because right now there is no rain on the horizon."
    • Unsu...

      Re: Plan on increasingly hot summers in LA

      Tue, October 28, 2008 - 11:18 AM
      Yeah, been reading that the concept of there being a "fire season" in SoCal has become a joke. Fire season is now a year-round affair. Good for the seasonal firefighters like my son in law I guess. Maybe he'll get a full-time position working for CDF if they'll be fighting fires all the time. earn that paycheck since I read that the state is just about out of unemployment benefit money anyway....

      I don't remember October 1965 but then I was only 11 years old. Must have been loving the warm weather since I was a little surf rat freezing my butt off out in the water. Don't remember if I had a wetsuit in those days, but wetsuits in 1965 were pretty cheesy. Beaver tails! I spent many days floating on a surfboard with ash floating down out of the sky and smoke-taste in my mouth from all the fires blowing from inland on the Santanas. Lots of memories of that! You could see the smoke clouds from the ocean that were burning the brushlands. Now all those brushlands are covered with tract home subdivisions plopped down in the canyons.

      Funny how that term has changed; now those winds are called Santa Ana winds and as a kid we always called them the Santanas.

      I have links to surf cams that dot the coast between La Push in Washington all the way to Mission Beach in San Diego where I grew up, and the sky in all of the SoCal cams have been a disgusting puke-green/brown haze most of the summer. Breathing this shit in and out of your lungs, ugh bad ewwww. A mix of recycled air through car engines and burning shit can't be good for ya! There's been days when I've popped in to see the ocean and the smog/smoke was so bad you couldn't hardly see the waves breaking...

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