But despite the general increase in rainfall, in almost any given year meteorologists can point to a region on the map that experienced drought. Precipitation patterns can vary widely on regional scales, from one season to the next, and from year to year. It is hard to predict accurately where and how much rain will fall next week. It is harder still to forecast next year's rainfall patterns. In the summer of 2000, drought hit hard in southeastern states like Georgia and Alabama while much of Texas has gone more than 67 consecutive days without rain.
Severe droughts kill crops, shrink lakes, and dry topsoil until it is carried away by the wind.
The resulting dust storms can damage many things in their path, and carry away valuable plant nutrients. Poring over data from satellite remote sensors, ground-based rain gauges, shipborne measurements, and even historical samples taken from sediment strata in dried rivers and lakebeds, researchers are painstakingly piecing together a picture of dry spells in North America. The goal is to use these new data to construct computer models that will help scientists predict the onset of a drought weeks, months, or even a year ahead of its arrival. A sophisticated system for measuring drought was developed by National Weather Service meteorologist Wayne Palmer in 1965. Called the Palmer Drought Severity Index, it uses temperature and rainfall information in a formula to determine dryness.