Published Tuesday, March 12,  2002 in the San Jose Mercury News


Region safe from drought that threatens other areas

Special to the Mercury News


While it appears that central and Northern California will have near-normal rainfall and an adequate snowpack, in other parts of the country they are using the dreaded ``D'' word -- drought.

The area of greatest short-term concern includes the Atlantic states from Maine to Georgia, where most areas are running four to six inches below normal rainfall for this time of year. However -- unlike the West, which is usually dry in summer -- this region gets as much precipitation in the spring and summer as in the winter and has more time to make up a water deficit.

The second largest area of drought conditions is in the northern Rockies, where the snowpack has lagged behind normal throughout most of the season, although recent storms have helped them catch up. Other pockets of below-normal rainfall include Southern California, the Southwest and the northern Plains.

Drought is more than just a deficit of rain or snow in a particular place. The condition is also largely dependent on the number and type of water-users, and whether only local water is used or if it is imported from other regions. Consequently, extended moisture deficiency can be thought of in terms of meteorological, hydrological, agricultural or socioeconomic drought.

Meteorological droughts are usually defined by the departure from normal precipitation on a monthly or seasonal time scale. Hydrological drought is primarily a function of the effect of precipitation on surface and subsurface water supply, but is also influenced by such factors as local water usage and storage.

Probably the most localized and fastest responding variety of drought is agricultural drought, which can vary from crop to crop and is measured on time scales as short as a week or two. How all of the above interact with human activity is reflected in a catch-all term, socioeconomic drought. That term is essentially a balance sheet of the supply and demand of water on residential, industrial and agricultural usage as well as its impact on hydroelectric power and energy conservation.

A good Web site to monitor all types of drought is

Q About four years ago, the PBS network had a most interesting program on El Niņo. Off the West Coast of South America, there is a tremendous amount of volcanic activity -- under water. They showed actual movies, taken under water, of this unbelievable power. This, of course, will heat up the water and produce the type of consequences you mentioned in your article. Would you elaborate on this source of nature's influence? I do not recall you making a point of this source of power.  John L. Ostrowski - Saratoga

A This theory has been floating around for a number of years, but it appears that the scale of undersea heat-venting and its timing do not support this being a causative effect of El Niņo. Submarine volcanoes can increase water temperatures on a local scale, but not enough to heat the 24,000 cubic miles of ocean water that are involved in an El Niņo event.

Over a very long period, sustained undersea venting can contribute to the heating and chemical makeup of the ocean. But this sort of impact would happen on a time scale of thousands of years. El Niņo events, on the other hand, occur on a time scale of months and last for only one or two years.

Q As a follow-up to your recent column on the Santa Ana winds of Southern California, I'd like to know why the Santa Anas are typically fiercer and produce much hotter temperatures in Los Angeles than comparable winds in San Jose and the Bay Area. If the unusually warm weather along coastal California in winter is primarily caused by the compression of air from the Great Basin down to sea level, I'd think the offshore winds should produce comparable effects in Southern California and the Bay Area. But such is not the case. There must be something else factoring into the equation. Steve Nolan  - San Jose

A Your observation is correct. The differences in offshore wind events here and in the southern part of the state are the result of several factors. When the Bay Area has warm offshore wind events, the air originates in northern Nevada and is somewhat barricaded by the Sierra Nevada. It also often mixes with milder near-surface air on its path toward the coast.

Finally, the air's trajectory from the Central Valley brings it over the East Bay hills, which have no significant canyons to funnel it down to sea level. Conversely, Santa Ana winds originate over the warmer high deserts of southern Nevada and the Mojave Desert and do not have to traverse the Sierra to reach the Los Angeles Basin. There, they get funneled down to near sea level by several east-to-west gaps like Santa Ana Canyon and San Gorgonio Pass.

Jan Null, founder of Golden Gate Weather Services is a retired Lead Forecaster with the National Weather Service. Send questions to him c/o Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif., 95190. You also can send questions via telephone (510-657-2246), fax (510-315-3015) or e-mail