/* Written 11:42 am Feb 23, 1991 by nsundt in cdp:en.climate */
/* ---------- "U.S. WESTERN DROUGHT" ---------- */
DROUGHT IN THE U.S. WEST
UPDATE #1
February 23, 1991
by Nick Sundt
Washington, D.C.
NATIONAL OVERVIEW
>From the very beginning of the en.climate conference in 1988, I have periodically posted information on the Western drought. Though I've posted very little on the issue since last Spring, the severity of the situation has reached the point where feel compelled once again to post the following
update.
I'll start at the national level, and with a glance back over the last five years. In 1987, drought conditions rapidly developed in portions of the United States; by the end of October, about 17 percent of the U.S. was in severe or extreme drought. Where normally one would expect to see considerable improvement in conditions during the winter and spring, this did not occur in late 1987 or early 1988. Instead there was only a small and partial recovery and by the end of January 1988, about 12 percent of the country still was in extreme or severe drought.
As many of you know, 1988 saw extensive drought in the U.S., with about 36 percent of the country in severe or extreme drought by the end of July 1988. Again, where a large recovery was expected by early 1989, drought conditions moderated only partially. By the beginning of April 1989, about 20 percent of the nation still was in severe or extreme drought. As in previous years, conditions worsened in the summer and again there was only a very small recovery by the end of the year.
The year 1990 also was very dry. Though the peak area covered by the drought conditions was not as high as in 1989 or 1988, there was no widespread recovery. The area of the country covered by drought never dropped below about 20 percent of the U.S. By the end of January 1991, roughly 18 percent of the nation was in extreme or severe drought.
During this time, the distribution of the conditions changed. Generally speaking, the drought has become more and more concentrated in the Western States. Much of the attention has focused on California, where the California Basin has experienced the driest October through January period since 1895. Making the situation particularly serious for California is the fact that this is the fifth year of drought in a row. Never before has the state seen such severe conditions.
But the drought conditions overlie much more than just California. As of January 19, 1991, extreme or severe conditions covered central and eastern Oregon, the east side of the Cascades in Washington state, much of southern and eastern Idaho, much of Wyoming, and North Dakota, and parts of Montana, Colorado, Utah, Nevada and a small part of Arizona.
In January 1991, much of the Far West received for the second straight month less than 50 percent of normal precipitation. This is the time of year when these states ordinarily receive most of their precipitation.
The mountain snowpack in most areas is below normal, frequently less than 70 percent of normal. Consequently, Spring and Summer Streamflows forecasts (as of 1 February 1991) in most of the West are far below average. Average or above average streamflows are mostly confined to an area running from north central Montana to Western Washington. Southern Colorado and Northern New Mexico also may see average or above average streamflows.
The prospects that heavy rain in the next few months will make up for the deficit are slim. The chances that many of the areas in southern Oregon, California, and Nevada will reach normal seasonal totals by the end of the rainy season range from 0 percent in Medford, Oregon (based on 42 years of data) to 20 percent in Long Beach, California (based on 88 years of data). In short, we will see another year of severe conditions in the U.S. West.
I will follow this paper up with additional statements during the next few weeks. These will explore some of the consequences of the drought for the Western states, and will include more detailed information on California. Taken as a whole, the information will provide a very sobering picture -- one with many interesting implications in the context of climate change.
Sundt, Nick. U.S. WESTERN DROUGHT. ECONET: List Owner davep@acsu.buffalo.edu. From: cdp!tgray@LABREA.STANFORD.EDU. Posted Sat, 23 Feb 91 15:16:47 PST on BITNET.
