Are tornadoes getting stronger and more frequent?
Are tornadoes and severe thunderstorms getting more numerous and more extreme due to climate change? To help answer this question, let's restrict our attention to the U.S., which has the highest incidence of tornadoes and severe thunderstorms of any place in the world. At a first glance, it appears that tornado frequency has increased in recent decades (Figure 1).
Figure 1. The number of EF-0 (blue line) and EF-1 and stronger tornadoes (maroon diamonds) reported in the U.S. since 1950. There is not a decades-long increasing trend in the numbers of tornadoes stronger than EF-0, implying that climate change, as yet, is not having a noticeable impact on U.S. tornadoes. However, statistics of tornado frequency and intensity are highly uncertain. Major changes in the rating process occurred in the mid-1970s (when all tornadoes occurring prior to about 1975 were retrospectively rated), and again in 2001, when scientists began rating tornadoes lower because of engineering concerns and unintended consequences of National Weather Service policy changes. According to Brooks (2013), "Tornadoes in the early part of the official National Weather Service record (1950-approximately 1975) are rated with higher ratings than the 1975 - 2000 period, which, in turn, had higher ratings than 2001 - 2007." Also, beginning in 2007, NOAA switched from the F-scale to the EF-scale for rating tornado damage, causing additional problems with attempting to assess if tornadoes are changing over time. Image credit: Kunkel, Kenneth E., et al., 2013, "Monitoring and Understanding Trends in Extreme Storms: State of Knowledge," Bull. Amer. Meteor. Soc., 94, 499–514, doi: http://dx.doi.org/10.1175/BAMS-D-11-00262.1
However, this increase may be entirely caused by factors unrelated to climate change:
1) Population growth has resulted in more tornadoes being reported.
2) Advances in weather radar, particularly the deployment of about 100 Doppler radars across the U.S. in the mid-1990s, has resulted in a much higher tornado detection rate.
3) Tornado damage surveys have grown more sophisticated over the years. For example, we now commonly classify multiple tornadoes along a damage path that might have been attributed to just one twister in the past.
Given these uncertainties in the tornado data base, it is unknown how the frequency of tornadoes might be changing over time. The "official word" on climate science, the 2007 United Nations IPCC report, stated it thusly: "There is insufficient evidence to determine whether trends exist in small scale phenomena such as tornadoes, hail, lighting, and dust storms." Furthermore, we're not likely to be able to develop methods to improve the situation in the near future.The current Doppler radar system can only detect the presence of a parent rotating thunderstorm that often, but not always, produces a tornado. Until a technology is developed that can reliably detect all tornadoes, there is no hope of determining how tornadoes might be changing in response to a changing climate. According to Doswell (2007): I see no near-term solution to the problem of detecting detailed spatial and temporal trends in the occurrence of tornadoes by using the observed data in its current form or in any form likely to evolve in the near future.
Are strong tornadoes increasing?
Stronger tornadoes (greater than EF-0 on the Enhanced Fujita Scale, or F0 on the pre-2007 Fujita Scale) are more likely to get counted, since they tend to cause significant damage along a long track. Thus, the climatology of these tornadoes may offer a clue as to how climate change may be affecting severe weather. Unfortunately, we cannot measure the wind speeds of a tornado directly, except in very rare cases when researchers happen to be present with sophisticated research equipment. Tornadoes are categorized using the Enhanced Fujita (EF) scale, which is based on damage (note that the EF scale to rate tornadoes was adopted in 2007, but the transition to this new scale still allows valid comparisons of tornadoes rated, for example, EF-5 on the new scale and F-5 on the old scale.) So, if a strong tornado happens to sweep through empty fields and never destroy any structures, it will never be rated as a strong tornado. Thus, if the number of strong tornadoes has actually remained constant over the years, we should expect to see some increase in these twisters over the decades, since more buildings have been erected in the paths of tornadoes. However, if we look at the statistics of U.S. tornadoes stronger than EF-0 or F-0 since 1950, there does not appear to be any increase in their number. Not surprisingly, a study accepted for publication in Environmental Hazards (Simmons et al., 2012) found no increase in tornado damages from 1950 - 2011, after normalizing the data for increases in wealth and property (note, though, that I am suspicious of studies that normalize disaster data, since they are prone to error, as revealed by a 2012 study looking at storm surge heights and damages.)
The future of tornadoes
An alternate technique to study how climate change may be affecting tornadoes is look at how the large-scale environmental conditions favorable for tornado formation have changed through time. Moisture, instability, lift, and wind shear are needed for tornadic thunderstorms to form. The exact mix required varies considerably depending upon the situation, and is not well understood. However, Brooks (2003) attempted to develop a climatology of weather conditions conducive for tornado formation by looking at atmospheric instability (as measured by the Convective Available Potential Energy, or CAPE), and the amount of wind shear between the surface and 6 km altitude. High values of CAPE and surface to 6 km wind shear are conducive to formation of tornadic thunderstorms. The regions they analyzed with high CAPE and high shear for the period 1997-1999 did correspond pretty well with regions where significant (F2 and stronger) tornadoes occurred. The authors plan to extend the climatology back in time to see how climate change may have changed the large-scale conditions conducive for tornado formation. Riemann-Campe et al. (2009) found that globally, CAPE increased significantly between 1958 - 2001. However, little change in CAPE was found over the Central and Eastern U.S. during spring and summer during the most recent period they studied, 1979 - 2001. A preliminary report issued by NOAA’s Climate Attribution Rapid Response Team in July 2011 found no trends in CAPE or wind shear over the lower Mississippi Valley over the past 30 years. However, preliminary work by J. Sander of Munich Re insurance company, presented at the December 2011 American Geophysical Union meeting in San Francisco, found that the number of days with very high CAPE values over the eastern two-thirds of the United States between 1970 and 2009 did increase significantly.
Del Genio et al.(2007) used a climate model with doubled CO2 to show that a warming climate would make the atmosphere more unstable (higher CAPE) and thus prone to more severe weather. However, decreases in wind shear offset this effect, resulting in little change in the amount of severe weather in the Central and Eastern U.S. late this century. The speed of updrafts in thunderstorms over land increased by about 1 m/s in their simulation, though, since upward moving air needed to travel 50-70 mb higher to reach the freezing level. As a result, the most severe thunderstorms got stronger. In the Western U.S., the simulation showed that drying led lead to fewer thunderstorms, but the strongest thunderstorms increased in number by 26%, leading to a 6% increase in the total amount of lighting hitting the ground each year. If these results are correct, we might expect more lightning-caused fires in the Western U.S. late this century, due to enhanced drying and more lightning.
Using a high-resolution regional climate model (25 km grid size) zoomed in on the U.S., Trapp et al. (2007) and Trapp et al. (2009) found that the decrease in 0-6 km wind shear in the late 21st century would more than be made up for by an increase in instability (CAPE). Their model predicted an increase in the number of days with high severe storm potential for almost the entire U.S., by the end of the 21st century. These increases were particularly high for many locations in the Eastern and Southern U.S., including Atlanta, New York City, and Dallas (Figure 3). Cities further north and west such as Chicago saw a smaller increase in the number of severe weather days.
Figure 3. Number of days per year with high severe storm potential historically (blue bars) and as predicted by the climate model (A2 scenario) of Trapp et al. 2007 (red bars).
Summary
We currently do not know how tornadoes and severe thunderstorms may be changing due to changes in the climate, nor is there hope that we will be able to do so in the foreseeable future. At this time, it does not appear that there has been an increase in U.S. tornadoes stronger than EF-0 in recent decades. Preliminary research using climate models suggests that we may see an increase in the number of severe storms capable of producing tornadoes over the U.S. late this century. However, this research is just beginning, and much more study is needed to confirm these findings.
References
Brooks, H.E., 2013, "Severe thunderstorms and climate change," Atmospheric Research, Volume 123, 1 April 2013, Pages 129–138, http://dx.doi.org/10.1016/j.atmosres.2012.04.002.
Brooks, H.E., J.W. Lee, and J.P. Craven, 2003, "The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data", Atmospheric Research Volumes 67-68, July-September 2003, Pages 73-94.
Doswell, C.A., 2007, "Small Sample Size and Data Quality Issues Illustrated Using Tornado Occurrence Data", E-Journal of Severe Storms Meteorology Vol 2, No. 5 (2007).
Del Genio, A.D., M-S Yao, and J. Jonas, 2007, Will moist convection be stronger in a warmer climate?, Geophysical Research Letters, 34, L16703, doi: 10.1029/2007GL030525.
Kunkel, Kenneth E., et al., 2013, "Monitoring and Understanding Trends in Extreme Storms: State of Knowledge," Bull. Amer. Meteor. Soc., 94, 499–514, doi: http://dx.doi.org/10.1175/BAMS-D-11-00262.1
Marsh, P.T., H.E. Brooks, and D.J. Karoly, 2007, Assessment of the severe weather environment in North America simulated by a global climate model, Atmospheric Science Letters, 8, 100-106, doi: 10.1002/asl.159.
Riemann-Campe, K., Fraedrich, K., and F. Lunkeit, 2009, Global climatology of Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) in ERA-40 reanalysis, Atmospheric Research Volume 93, Issues 1-3, July 2009, Pages 534-545, 4th European Conference on Severe Storms.
Simmons, K.M., Dutter, D., and Pielke, R., 2012, "Normalized Tornado Damage in the United States: 1950-2011," DOI: 10.1080/17477891.2012.738642
Trapp, R.J., N.S. Diffenbaugh, H.E. Brooks, M.E. Baldwin, E.D. Robinson, and J.S. Pal, 2007, Severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing, PNAS 104 no. 50, 19719-19723, Dec. 11, 2007.
Trapp, R. J., Diffenbaugh, N. S., & Gluhovsky, A., 2009, "Transient response of severe thunderstorm forcing to elevated greenhouse gas concentrations," Geophysical Research Letters, 36(1).
Jeff Masters
Reader Comments
Page: 1 | 2 | 3 | 4 | 5 | 6 — Blog Index
Starting to get mammatus clouds overhead....strong storms already on shore approaching......getting nasty
So far this year tornado wise has been active. I cant wait to find out how active it is in early may (not).
The last time we saw this much early activity was, unfortunately, 1999.
234 tornadoes in Jan. & Feb. 1999
There definitely is a correlation between early activity and a strong La Nina event. 1974, the year of the Super Outbreak, was also a La Nina year: Link. So yes, I'm afraid someone may be in for it this year. I hope I'm wrong.
I took a second look at my Tornado History Project link for 1999. There was one violent tornado in January-February. This year we've had five already, and we've obviously not had 5x as many tornadoes. This is disturbing.
Pardon my ignorance, but what tornado are you referring to when you say "largest and strongest in history"?
From thunderstorms this morning to heavy snow warnings and winterstorm warnings.
Western slopes of N.C.= 6-12inches(+3000f.t)
Mountains 3000f.t to around 2100f.t. 2-4inches
Foothills 1500f.t to 2000f.t. 1inch possibal.Below 1500, wind snow.
Piedmont. Slight chance of a flurrie.
Also, the mountains will get gust over 55mph with all that snow.
Pardon my ignorance, but what tornado are you referring to when you say "largest and strongest in history"?
I was referring to the Greensburg tornado, which was 1.7 miles wide (I don't think there ever was an F5 tornado that big before; of course, when I say "largest and strongest" I mean both).
Sounds like a hurricane on land that size.......wow
I was referring to the Greensburg tornado, which was 1.7 miles wide (I don't think there ever was an F5 tornado that big before; of course, when I say "largest and strongest" I mean both).
Ah, I gotcha. I thought of the Tri-State Tornado, and looked it up, but it seems that it was "only" a mile wide as well.
I wonder just how intense the Mulhall tornado of 1999 truly was. It was rated F4, but chaser Roger Edwards thought it might have been more violent than the Moore tornado. A shame we'll never know for sure. They need to do more quantitative measurements of tornadoes.
This is ESPECIALLY true of hurricane frequency. Before satellites, we had to rely on ship reports/landfalling storms and thus there could be a large number of hurricanes unaccounted for....This is why we just dont know whether hurricanes through long term, have been increasing/decreasing in general in any specific pattern.
"I have a question here for those in the know as I don't have a clue on where to look this information up. I need to drive a vehicle west originating from northeastern Ohio. I can either drive due west or take a more southern route by heading to Kentucky first and then heading west. Of issue is the fact that this vehicle is not snow worthy. Also, while I do not have to pick it up immediately, I also do not want to leave it there for very long. So, I've been trying to find any place listing the average date of the last snowfall in Ohio as well as any somewhat reliable 30 day long range forecasts for Ohio and neighboring states. I know long range forecasts are anyone's guess, but I'm sure there's probably someone's forecast out there that members here would tend to bet on more than others. I'm hoping to be able to pick up the car some weekend in March or the first week of April. As airlines charge a bunch of money when buying a ticket last minute, I'm wanting to try and pick the likely best weekend so I can buy my ticket with a little lead time and get a much cheaper rate. I'd be flying into Ohio on a Friday and driving west on the weekend. Anyone have any educated guesses on which weekend in March or maybe even first week in April might be best?"
Link
Interestingly, similar vorticies are suspected within hurricaine eye walls, which may account for the variation in damage.
You can usually get cheap tickets with little advance notice on priceline. I don't know how they do with one-way, but a round trip might be similar in price. You have to bid on the flights, though. Oh, and depending on where you are coming from, it might be cheaper to fly into CAK than CLE. Check both. Flying into Pittsburgh would almost certainly be cheaper, but it's a bit of a haul from there to here. (ca. 100mi.)
Just so you know, here in northeast Ohio, we can get snow as late as early May, and April snows are common.
Wasn't that a bit rude, Taz? >_>
6:56 AM AST WEDNESDAY, FEBRUARY 27, 2008
GULF OF MEXICO/NORTHWEST ATLANTIC OCEAN WEST OF 50W....
An upper trough is situated over the Eastern half of the CONUS with the associated cold front pushing across the Gulf Mexico from the Tabasco Plain in the Southern Bay of Campeche to the Florida Peninsula and beyond. The front lies within a southwesterly upper flow regime between the associated upper trough and a weak ridge across the Caribbean. Scattered to broken multilayered cloudiness and embedded showers lies within 200 nm of the frontal boundary from Southeastern Mexico to the Western Atlantic, while covering the entire Florida Peninsula. Meanwhile, the associated surface high-pressure anticyclone is established 1030 mb over Eastern Texas at 31N/93W. This high is producing exceptionally fair and tranquil conditions over Northern Mexico, much of Texas, the Deep South, Southeast United States and the northwest corner of the Gulf behind the swath of moisture. The high is also producing a strong offshore flow with northerly winds of 25-35 knots and swells of 14 ft mainly west of 90W. As the front moves across the area these conditions should push into the Bay of Campeche and then the Gulf of Tehuantepec in the next 24 hrs. Expect storm force conditions and further upwelling within the Eastern Pacific Ocean. Expect 3-6 ft seas elsewhere across the Gulf waters but increasing to 6-10 ft as the front moves by.
The cold front continues from Central Florida northeastward to a 985 mb low over the Northeast United States near 41N/66W. This section of the front lies within a very favorable upper level environment with ample upper divergence and as a result scattered moderate to strong showers and thunderstorms lies along the front. Further east, a weak surface high is responsible for the weak surface pressure pattern across the Atlantic ahead of the front with 5-10 knot return flow and mainly fair weather.
CENTRAL AMERICA AND THE CARIBBEAN REGION....
Due to the weakening of the subtropical ridge north of region, trades have now decrease to easterly at 10-15 knots and swells are now 3-4 ft and only 7 ft along the Colombian Coast. The bulk of the unsettle weather will be situated in the Northwest Caribbean where the cold front will enter the region bringing increase shower, wind and wave action. As for the remainder of the Caribbean, upper ridging and dry air will continue to maintain a stable airmass over much of the region, resulting in fair weather. Additionally, periods of brief passing showers can be expected across the Lesser Antilles and the Eastern Greater Antilles where the trades are advecting widespread patches of shallow moisture.
by W456
Viewing: 51 - 101
Page: 1 | 2 | 3 | 4 | 5 | 6 — Blog Index