"The slope of the line is much steeper, and long-term drought is what's driving it," said Kirk Rowdabaugh, deputy state forester for Arizona.

Cape Verde's low per capita GDP reflects a poor natural resource base, including serious water shortages exacerbated by cycles of long-term drought.

The long-term drought and the consequent drop in food production exacerbated this problem during the early 1980s.

You can be in the middle of a long-term drought and still get enough rain to produce your crops.

Unlike many other states, Maine has few large aquifers to provide an insurance policy against long-term drought, said Mr. Lent at the Geological Survey.

Trees throughout Africa's Sahel region - vital to peoples' livelihoods - are dying as a result of long-term drought linked to climate change, according to a study.

"I'm a believer that history repeats itself - long-term drought could return," Mr. Thompson said.

The index has proven most effective in determining long-term drought - a matter of several months - and not as good with conditions over a matter of weeks.

"While flooding caused many problems, the good news is that these totals have finally started to put a dent in the long-term drought that has persisted in this region," the report said.

The long-term drought has drawn down groundwater.