The Forecast for U.S. Weather Catastrophes

The frequency and damages associated with weather catastrophes are expected to increase due in part to manmade climate changes and socioeconomic factors, according to Mark Bove, senior research meteorologist of Catastrophe Management for Munich Reinsurance America.

“The first 11 years of the new century have been very active for natural catastrophes worldwide and in the U.S., as well,” Bove said. “We’ve had major flooding in Europe, Pakistan and Australia. We’ve had major earthquakes starting with the Indian Ocean tsunami in 2004, the Japan earthquake and tsunami last year and major earthquakes in Chile and Haiti.”

In the U.S., the latest century weather-related catastrophic losses began in 2004, Bove said.

The 2011 thunderstorm season was significant in that it produced the single largest insured event due to a single tornado – Joplin, Mo.

Hurricane Charlie, which hit on August 13, 2004, was the strongest hurricane ever in terms of sustained wind speeds to make landfall since Hurricane Andrew in 1992, generating $8 billion in damage.

“The next six weeks proved to be even more catastrophic as three more hurricanes hit the state of Florida over the next few months in total incurring $25 billion of insured loss,” Bove said.

Hurricane Katrina that hit in 2005 remains the world’s largest insured loss due to any natural catastrophe at $60 billion. That year hurricanes Rita, Wilma, and Dennis also caused major losses along the Gulf Coast.

“Eight of the top 10 insured losses that have occurred in the past decade have affected the U.S,” Bove said, pointing out that seven of the 10 were related to hurricane landfalls.

There are numerical weather models that can be used to predict meteorological events, but each requires large amounts of data, Bove said.

“With most perils we do have the ability to forecast and predict them to help prepare for natural disasters.”

According to Bove, the reason the models are so good is because:

• Of a rapid increase in computer technology
• They are more sophisticated models
• They have faster run times
• The emergence of satellite remote observation technology
• The rapid increase of meteorological and oceanographic observation and data (both on the planet and by observing it via satellites.)

Ensemble modeling is also used to plot the course of weather-related perils. This model is also known as a spaghetti plot. It can run multiple models at once and compare the general area.

“The more closely spaced these model tracks are the more confidence you can have in the results,” Bove said.

Because it reduced the uncertainty in location, it’s considered the greatest success story of hurricane modeling, the senior research meteorologist said.

According to Bove, the intensity forecast hasn’t gotten better. This is because the steering currents that affect storms, the heat flux from the ocean and the intensity of a hurricane’s eye wall are not yet well understood.

While improvements have been made in daily forecasts, some limitations remain.

In addition, there are natural climate cycles that affect catastrophes. According to Bove, when the El Nino (ENSO) climate pattern is in effect, fewer Atlantic hurricanes can be expected. The opposite is true of the La Nina climate pattern.

Another factor affecting storm severity is the North Atlantic Oscillation (NAO), essentially the pressure difference that when positive equates to more storm activity, and when negative equals less storm activity.

Over decades, the tropical Atlantic sea surface temperature, known as the Atlantic Multidecadal Oscillation (AMO), can vary considerably. This, too, can affect storm activity:

During El Nino, there is a reduction of thunderstorms over Texas and the southern states. During La Nina, there is an increase over the Deep South and Ohio River Valley. Bove cites the examples of 1974’s deadly storms super outbreak and 2011’s tornado outbreak, both seasons coming off La Nina winters.

Evidence suggests manmade changes are affecting the weather at an increasing rate of change, according to Bove. “Carbon dioxide levels are at an all-time high.”

“Extra carbon does not allow all of the heat from the sun to radiate back out into the atmosphere,” said Bove. This is most visible at the north and south poles. Most heat received at the equator is transferred out of the poles.

As a result, the ice cap is disappearing quickly. According to Bove, by some estimates there will be no ice by 2030 at the North Pole during winter.

The result will likely be more intense weather, he said. Wet places will become wetter, while arid climates will become even hotter.

Notably, there have been 171 natural disaster events in the past 30 years between 1980 and 2011, Bove said; this is a marked increase in meteorological storms compared to geophysical perils, such as earthquakes, tsunamis and volcanic eruptions.

Some examples of socio-economic trends affecting an increase in weather-related damage and losses include:

Flooding:

• Suburban sprawl more cases for severe flooding
• Reduced natural drainage patterns
• Developments on flood plains
• Potential for levee failures

Drought:

• Agriculture
• Wildfires
• Business interruption – hydroelectric and nuclear
• Resource reduction – water for commercial, agricultural and industrial businesses

According to Bove, urban sprawl into wilderness areas in California combined with drought in the Southwest have led to larger and more frequent losses due to wildfires. Coupled with a storm cycle, the lack of brush and heavy rains may cause landslides.

Besides urban sprawl, Bove cites poor building practices and building age as other socio-economic factors increasing national catastrophe losses.