The nation has experienced a stunning increase in federal disaster declarations for tornadoes in the 21st Century.

In the 30 years from 1953 — when the Federal Emergency Management Agency began keeping score —  through 1982, FEMA issued an average of 27 tornado-related disaster declarations annually, according to FEMA figures.

In this millennium, that average has more than quadrupled, to 118. That's the result of human activity — and not necessarily anthropogenic warming.

The evidence is quite unclear regarding the effects of rising temperatures on tornadoes, and data show little change in the last 55 years in trends for the strongest ones.

The government certainly has become more generous in awarding disaster assistance, and that's likely a factor in the bump in the disaster numbers. But the quadrupling bears a remarkable similarity to another figure.

Since 1950, says Stephen Strader, an assistant professor in Villanova University's department of geography and the environment, development in the contiguous 48 states, home to one of the world's most-fertile tornado spawning grounds, also has more than quadrupled.

By his estimate, only 5 percent of the land mass was considered developed in 1950; by 2010, that number was 22 percent, and a lot of building occurred in some of the world's most fertile spawning grounds for tornadoes.

In papers published recently he has warned that tornado damages could triple by the end of the century, even if tornadoes don't get an extra kick from a warming trend. Things would be worse, of course, if they do.

"We build ourselves into disasters," he says. "Disasters are socially constructed."

In the case of tornadoes, the remedies are elusive. In areal coverage most of them are small storms funneling along narrow paths. The odds against any given building getting hit are infinitesimal.

But year after year, buildings do get hit, and people get killed. One thing local governments could do is place more emphasis on storm shelters, advises Strader.

The most-vulnerable areas are in the Midwest and South, but tornadoes have occurred in every state. Even Pennsylvania.

In 1994, a powerful tornado killed three people who lived in Limerick Township, Montgomery County, in a recently built development.