More of the “extreme events” meme…
From the AGU weekly highlights
Regional models expect drier, stormier western United States
Key Points
- Statistically significant increases in western US future extreme winter precipitation
- Eight dynamically downscaled GCM simulations show generalized agreement
- Spatial pattern of changes in mean precip. is different than that of extremes
As American southwestern states struggle against ongoing drought, and the Northwest braces for a projected shift from a snow- to a rain-dominated hydrological system, climate researchers strive to provide precipitation projections that are fine grained enough to be of value to municipal water managers. Estimates derived from large general circulation models show that in a warming world, water availability in the western United States will be increasingly dictated by extreme events.
However, such large models tend to lack necessary detail for the small-scale interactions and topographic influences that dominate daily changes in local precipitation. To convert the broad predictions of global models into practical predictions, Dominguez et al. used an ensemble of regional models, set to fit within the projections of general circulation models, to estimate future winter average and extreme precipitation for the western United States.
The authors find that for the years 2038–2070, winter average precipitation in the southwestern states would be 7.5 percent below 1979–1999 levels. They also find, for the entire areal-averaged western United States, a 12.6 percent increase in the magnitude of 20-year-return-period winter storms and a 14.4 percent increase for 50-year winter storms. In some regions, like southern California and northwestern Arizona, this increase in strength of 50-year storms was pushed as high as 50 percent. Though the temporal and spatial granularity of the regional climate models is much improved over that of general circulation models, workable and useful measurements for hydrological engineering and water management design will need ever-better estimates of future rainfall patterns.
Source:
Geophysical Research Letters, doi:10.1029/2011GL0507624, 2012
Title:
“Changes in winter precipitation extremes for the western United States under a warmer climate as simulated by regional climate models ”
Authors:
- F. Dominguez, E. Rivera, and C. L. Castro
- Department of Atmospheric Sciences, University of Arizona, Tucson, Arizona, USA;
- D. P. Lettenmaier
- Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA.
Abstract:
We find a consistent and statistically significant increase in the intensity of future extreme winter precipitation events over the western United States, as simulated by an ensemble of regional climate models (RCMs) driven by IPCC AR4 global climate models (GCMs). All eight simulations analyzed in this work consistently show an increase in the intensity of extreme winter precipitation with the multi-model mean projecting an area-averaged 12.6% increase in 20-year return period and 14.4% increase in 50-year return period daily precipitation. In contrast with extreme precipitation, the multi-model ensemble shows a decrease in mean winter precipitation of approximately 7.5% in the southwestern US, while the interior west shows less statistically robust increases.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Woot Benjamin
There is set of historical records that tabulates Southern California rainfall and rainfall proxies (e.g. Mission crop records) from 1769 to 1930: “Rainfall and Stream Run-Off in Southern California Since 1769” by H. B. Lynch, August 1931, for the Metropolitan Water District of Southern California. The report is available on-line at
http://cepsym.info/history/RainfallStreamRunoffSoCA_since1769.pdf
and
http://books.google.com/books/about/Rainfall_and_stream_run_off_in_Southern.html?id=sJMJAQAAIAAJ
CA Department of Water Resources developed a correlation between the “Lynch Index” in the report and the overlapping precipitation record for a Los Angeles gage to develop a continuous 230 year precipitation record from 1769 to 2000. The slope of the linear regression through the data is very close to zero.
The Foreward and Summary of Conclusions are informational and even inspiring: “California has always had its climate, but has had rain gauges in any large number for only about fifty years. A few series of measurements go back to the time of the discovery of gold; not one antedates that period. California history previous to that era, however, when carefully studied, yields an amazing amount of data to take their place. For many reasons, the early history of California is known in a detail, and with an exacitude approached in but a few other places. It is a fascinating, and intensely human subject, and in the documents which form its sources, along with the usual matters of interest to the formal historian, there is unfolded the story of weather conditions here for the eighty years of recorded history prior to Marshall’s discovery of gold, with a minuteness which cannot be appreciated until it has been gone into thoroughly.”
“Times of drought and of plenty are pictured from many different points and in many different ways, but they never form an inconsistent story.”
“1. There has been no material change in the mean climatic conditions of Southern California in the past 162 years.”
“3. The twenty-eight year period of rainfall deficiency which ended in 1810 was about as severe as has been the present one to date, and much more protracted.”
“4. The period of rainfall surplus from 1810 to 1821 was more intense than anything in the past forty years. It seems to have been about as intense as was that between 1883 and 1893.”
“5. The period of rainfall deficiency which lasted from about 1822 to 1832 was more severe than has been any occurring since.”
“6. The period of rainfall deficiency which commenced in 1842 and lasted until 1883 was much longer than any other of which we have record. It was not so acute, however, as some others, both earlier and later. It was broken by a period of normal rainfall, but was without any periood of excess rainfall to balance the deficiency.”
“The Spanish missionaries arrived in California in May, 1769, in a period of excess rainfall.”
So I ought to expect heavy rains, massive flooding, and cold weather here in California, then?
I’d like to put a smiley on it, but given their track record, and inversion seems more accurate…
Someone spent money to find out something that was already evident?????? Again??????
“Abstract
Changes in total solar irradiance can be linked to changes in regional precipitation. A possible mechanism responsible for this linkage begins with the absorption of varying amounts of solar energy by the tropical oceans which creates ocean temperature anomalies. These anomalies are then transported by major ocean currents to locations where the stored energy is released into the atmosphere, altering atmospheric pressure and moisture patterns that can ultimately affect regional precipitation.”
http://ks.water.usgs.gov/waterdata/climate/homepage.ijc.html#HDR0
Feedback mechanisms
Former senior CSIRO scientist, Dr Ken McCracken, who has expertise in solar and cosmic ray physics, says the new research shows that climate feedback mechanisms can have a very significant effect.
He says Arblaster and colleagues’ research shows there is roughly a two and half fold amplification of the sun’s energy.
“It’s a bloody big effect,” says McCracken, who is now affiliated with the University of Maryland in the US.
http://www.abc.net.au/science/articles/2009/08/28/2667549.htm
Ya know, if these folks that publish this stuff would spend as much time reading literature as they do modeling they might learn something.
http://tenaya.ucsd.edu/~dettinge/PACLIM/Yu02.pdf
Record rainfall for March here in Portland: http://www.accuweather.com/en/weather-news/rainfall-records-set-in-oregon-1/63533
fyi.