Environmental Economics

I've been noticing them all the time!

The number of tornadoes recorded by the National Climatic Data Center has increased in recent years, but that doesn’t mean there have been more twisters.

“The changes there are huge but almost certainly due to reporting changes,” said Harold Brooks, a scientist with the National Severe Storms Laboratory who studies tornadoes and other severe weather with hail or high winds.

When climatologists want to gauge global changes in weather, they rely on temperature and precipitation, which can be measured at regular intervals at thousands of fixed weather stations around the world.

Tornadoes are tougher.

Some areas are prone to the ferocious storms, but it’s impossible to know exactly when or where they will occur, making them difficult to count. If they pass quickly, do no damage, or occur in an area with few or no people, they may not be counted at all.

Even when they are spotted, the mechanism for reporting the storms is ad hoc.

Tornadoes recorded by the National Climatic Data Center are documented variously by trained spotters, newspaper accounts, utility workers, pilots, the general public, fire fighters, police and others.

Climatologists and meteorologists now benefit from tools such Doppler radar, but advances in technology may mean that weaker tornadoes are more likely to be reported.

Such circumstances make it difficult to say with any certainty whether the frequency of tornadoes has increased over time, or whether storm reporting has simply gotten better.

via blogs.wsj.com

I like this picture:

If people report tornados and population is increasing, then the number of tornadoes will increase just from population growth. I decided to try to estimate that relationship so I went to the NCDC, searched for tornado and clicked on Historical Records and Trends. Here is the first image I see:

Here is what the NCDC says about the lack of trend:

With increased National Doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency. To better understand the variability and trend in tornado frequency in the United States, the total number of EF-1 and stronger, as well as strong to violent tornadoes (EF-3 to EF-5 category on the Enhanced Fujita scale) can be analyzed. These tornadoes would have likely been reported even during the decades before Doppler radar use became widespread and practices resulted in increasing tornado reports. The bar charts below indicate there has been little trend in the frequency of the stronger tornadoes over the past 55 years.