The Golden State is called this not
only because of the Gold Rush, but also because of its mediterranean climate,
characterized by winter rainfalls, and prolonged dry season that runs from
the end of March until October, during which time the hills and valleys
turn a characteristic Golden Brown.
My colleague, James Goodridge, retired California State
Climatologist, has collected and collated many thousands of time series
of California's rainfall, climate and hydrostands. He shares these freely,
and in the recent few years has also compiled some interesting commentary
about extreme events, some of which I share with you herein, in respect
for Jim's interests in similar phenomena, and the oceanography that portends
such major events. A relativly recent update of his perspectives, entitled
Historic Rainstorms in California, dated August 1997, is available
from the State of California Department of Water Resources, Bulletins and
Reports, P.O. Box 94236, Sacramento, CA 94236-0001. Its Free, too!
Jim Goodridge - and many other climsate researchers
- are well aware of the role of the oceans in the hydrologic cycle. There
are many ongoing efforts to decipher the longer-term patterns that precede
major weather events, although the problem remains the poverty of historical
data.
Since climate (weather) is so variable, its study and
eventual opportunity to forecast will require many iterations of each type
of signal before the various time and space scales of forecasts will gain
credibility.
In perusing the records of Historic 1000 Year Return-Time
Storms of California that Goodridge uses and presented at the 1996 Pacific
Climate Conference I was pleased to find adequate information to be able
to point out that there is much more to California's rainfall than only
El Niño.
For example, in spite of the propensity for agency
climatologists to begin their summaries in the data rich 1947-1950 post
war period, and bring them forward, the Comprehensive Ocean and Atmosphere
Data Set, or COADS as it is better known, allows one to revisit data from
ocean observations made by sailing ships since 1854 - and today's modern
ocean-going vessels. This permits some reconstructions, particularly useful
to studies of ENSO and other global climate phenomena.
The Southern Oscillation Index has been reconstructed
back to 1882 from COADS, when the SOI reached a low of -1.6 in June (on the unexpanded scale),
from which one would infer an El Niño was in progress.
The Australian Bureau of Meteorology uses a slightly
different method for calculating monthly
mean SOI values, and updates them regularly, around the end of the
first week in each month after. I try to keep these updated
records available on my web-site, too.
Similarly, low values occurred in the years 1889, 1891,
1896, 1900-01,
1905, 1911-13,
1918-1919, 1925-26, mid 1939-1941, 1946, 1948-49, 1951,
1953, 1957-58,
1963, 1965-66,
1969, 1972, 1977-78,
1979-80, 1982-83, 1986-87, late 1989-90,
and after a brief respite, the period from July 1990 until fall of 1994
remained below zero, with seasonal rises. The event of 1997-98 - well below zero, and likely the
strongest of the century's warm Events, was followed by a similarly remarkable
period of Cooling of the North Pacific, as well as an apparent shift in
the Pacific Decadal Oscillation, the Atlantic Oscillation, and several
other climate indices, including the Vangeneim-Girs ACI, indicating a general
Climate Regime Shift has likely taken place.
The Periods marked in yellow indicate El Niños initiating
in or about March of each year, and the blue
marked events were remarkable only in their being
periods of below zero, but without large deviations. The month of June
is the most common month when the SOI dips below the zero point - leading
into many of the more protracted Events.
To attempt any sort of
analysis it is wise to begin with some sort of hypothesis.
In this case I have selected the one being promoted
by those pushing for the 1997-98 ENSO Warm Event to be a disastrous year
for California due to extreme rainfall. One alternative being simply that
greater or similar rainfalls can also occur in the Cool eastern tropical Pacific period preceding
these ENSO Warm Events, often called La
Niña.
From the 1878 to 1994 COADS SST anomaly records provided
by Allan et al. (1997), and the SOI reconstruction reaching back only to
1882, I have reviewed Goodridge's summary of major events, and found the
following results:
While much of what we worry about is
focused on the local geographic region, including the Offshore Ocean, as is one important aspect of the climate and weather picture,
there are other, more important scales to keep informed about, as the local
weather reflects both ocean and global responses to solar forcing.
One should never forget
that the sun is the Earth's heat engine!
The rainfall information used in this document are
freely available from James Goodridge, at <jdgoodridge@sunset.net>.
A similar series of studies by Oregon State Climatologist,
George Taylor with some cogent comments and time series are available at:
http://www.ocs.orst.edu/reports/wet-dry.html
My final comments are about the fact that we have yet
to observe or measure the full extent of natural climate variability, here
or anywhere on earth. These mere century-long records provide some feel
for the melange of different processes and Events that can affect our lives.
The storm of December 23, 1861 to January 21, 1862 was said to have inundated
the entire central valleys, the Sacramento and San Joaquin, an extent of
250-300 miles, averaging 20 miles in breadth. The floods destroyed the
entire commerce of the state. One needs to become a bit wary of each Dooms-Day
statement about El Niño, given that it appears that there is more
to the problem than just equatorial warming.
In fact, the greatest storms appear to be associated
with either Pre-Niño conditions (e.g., January 1911, 1943, December
1955, December 1996-January 1997), far west of Hawaii - or Autumn (August
to October) tropical storms emanating from the eastern Pacific Ocean south
of Mexico, that follow warm surface waters within the eastern tropical
Pacific Ocean, along the coastline - until they make landfall. Some years
they make it as far north as mid-California (1918). In others they cause
havoc in Mexico (1997).
Water is Life! Water is also Disaster - unless you
are prepared for it.