Future Storminess in a Warmer World

James B. Elsner, Earl and Sophia Shaw Professor & Chair, Geography Department

March 5th, 2018

Lecture Notes

myweb.fsu.edu/jelsner/Day3.html

  • Heat & hurricanes: Connecting the dots.
  • Rising hurricane damage.
  • Fewer but stronger.
  • More tornado energy.
  • Fewer days but bigger outbreaks.
  • Who survives? Tornado vulnerability.

Last week

Fewer Tornado Days But Bigger Outbreaks

  • Strict focus on frequency limits how to understand a changing storm climate.
  • Absence of an upward trend does not imply that tornado climate is stationary.
  • Number of tornado days and where they occur.
  • No theory exists for climate change impact on tornadoes. Brand new field of study.
  • Storm Prediction Center (SPC) data.
  • Better technology means more tornado reports.
  • Damage rating scale first published in 1971.
  • A small, brief tornado may go unreported. Population bias.

Changes

Distances are in kilometers

But the Bias Is Decreasing

Population

They Are Coming In Bigger Bunches.

Large-Scale Hypothesis

  • An explanation for the increasing efficiency (more big tornado days) is simply larger areas favorable for tornadoes.
  • We call this the large-scale hypothesis because it hints at the involvement of larger scale dynamical factors like wind shear as the cause.
  • To examine evidence for this hypothesis, here we consider changes to the spatial dimensions of tornado occurrences.
  • But what do we mean by a tornado cluster?

Example: May 8, 2008

All Clusters (1954--2013)

No Trends

Large Increases in Tornado Density

Summary

  • It appears that the risk of big tornado days with densely packed clusters of tornadoes is increasing.
  • The increasing density of tornado occurrences within clusters suggests that the explanation for an increasing proportion of tornadoes occurring on big days might involve local-scale thermodynamics.
  • I suggest that increases in both CAPE, driven by increases in low-level moisture, and CIN, driven by warming aloft, could lead to fewer days with tornadoes and to smaller, but more active, areas of severe convection on days with tornadoes.

Who Survives?

  • A 10 mobile home increase under the path increases the casualty rate by 4.2%
  • A 100 person increase in the population over 65 under the path increases the casualty rate by 1.4%
  • A percentage increase in the white population under the path decreases the casualty rate by 25%

Terms can be added to models to better understand the impact demographic and socioeconomic variables have on tornado casualties.

Estimates of interest include:

  • Young and old population
  • White and black population
  • Household median income
  • Mobile homes
  • A 10 mobile home increase under the path increases the casualty rate by 4.2%
  • A 100 person increase in the population over 65 under the path increases the casualty rate by 1.4%
  • A percentage increase in the white population under the path decreases the casualty rate by 25%
  • When controlling for the number of mobile homes, household median income IS NOT a significant factor
  • Older populations (over 65) are a stronger predictor than younger populations (under 17)
  • White populations are a stronger predictor than black populations

The Future

  • Welcome to the age of climate disruption and migration.
  • Climate change displaced more than a million people from their homes last year. It could soon reshape the nation.
  • Storms (hurricanes, tornadoes, fire) will be a big reason (e.g., Hurricane Maria and Puerto Rico).

Thank You!