El Niño is actually a warming of the waters off of
South America associating with a reversal of the prevailing winds in the area. This change, often of only a few degrees, modifies
weather patterns all over the world. Because the water is warmer, more
convection occurs over the water and more
moisture is drawn north towards
southern california, creating flooding and excessive rain here. El Nino also causes heavy
rain in other southern states as the storms move east. El Nino in the
Northwest often brings
drought as storms stay south.. it is also charactarized by mild
winters in the North, and decreased
hurricane activity in the Atlantic.
lately there have been several severe El Nino episodes, and also the occurence of El Nino, usually once every 7 years or so, has been more frequent lately. This is just further evidence that the Earth's climate is very changable.. some believe greenhouse warming modifies El Nino but that is yet to be seen. Regardless of all of this, during the winter of 1997 severe flooding in California brought a spotlight to El Nino when it entered the eyes of popular culture.
Update: As of Fall 2001, it looks like El Niño is making a comeback... However, it doesn't appear that this El Niño will be as strong as the previous one in 1997.