15 February 2012

New Peer-Reviewed Paper on Global Tropical Cyclone Landfalls

We have a new paper just accepted for publication in the Journal of Climate, titled "Historical Global Tropical Cyclone Landfalls." Here is the abstract:
Historical global tropical cyclone landfalls
Jessica Weinkle, Ryan Maue and Roger Pielke, Jr.
Journal of Climate (in press)

In recent decades, economic damage from tropical cyclones (TCs) around the world has increased dramatically. Scientific literature published to date finds that the increase in losses can be explained entirely by societal changes (such as increasing wealth, structures, population, etc) in locations prone to tropical cyclone landfalls, rather than by changes in annual storm frequency or intensity. However, no homogenized dataset of global tropical cyclone landfalls has been created that might serve as a consistency check for such economic normalization studies. Using currently available historical TC best-track records, we have constructed a global database focused on hurricane-force strength landfalls. Our analysis does not indicate significant long-period global or individual basin trends in the frequency or intensity of landfalling TCs of minor or major hurricane strength. This evidence provides strong support for the conclusion that increasing damage around the world during the past several decades can be explained entirely by increasing wealth in locations prone to TC landfalls, which adds confidence to the fidelity of economic normalization analyses.
In the paper we provide details on landfalls of tropical cyclones (called hurricanes in the Atlantic) for the five major global basins and a global aggregate from 1970 (in the figure shown above -- the paper provides similar graphs for each of the basins for the periods of available data). We take the Atlantic back to 1944 (no other basin has reliable data before 1950, so earlier data is superfluous for our analysis), though the record of US landfalls goes back before 1900 and has been discussed in other papers (like this one in PDF).  Tropical cyclone statistics are a cherry picker's delight because large intra-basin variability means that "trends" can be found (up and down) over various arbitrary periods of record. For instance, we do see a upwards trend in North Atlantic landfalls since 1970, but not since 1944 (or 1900). Other basins show similar up-and-down pattens on multi-decadal periods, but we finding nothing coherent at the global level. Over 41 years of reliable data, there is precious little evidence of a secular trend at the global level.

A reviewer wisely noted that looking for linear trends in such data was probably not particularly useful in any case -- and we much agree, however, a detection of trends is (for better or worse) established by the IPCC as a means to detect of changes in climate. Those looking for meaningful trends in TC behavior (regardless of cause) should be aware that even assuming large changes in storm behavior, such trends would not be detectable for many decades or longer. Thus, our findings should not be too surprising.

Some interesting statistics of note:
  • Over 1970 to 2010 the globe averaged about 15 TC landfalls per year
  • Of those 15, about 5 are intense (Category 3, 4 or 5) 
  • 1971 had the most global landfalls with 32, far exceeding the second place, 25 in 1996
  • 1978 had the fewest with 7
  • 2011 tied for second place for the fewest global landfalls with 10 (and 3 were intense, tying 1973, 1981 and 2002)
  • 1999 had the most intense TC landfalls with 9
  • 1981 had the fewest intense TC landfalls with zero
  • There have been only 8 intense TC landfalls globally since 2008 (2009-2011), very quiet but not unprecedented (two unique 3-year periods saw only 7 intense landfalls)
  • The US is currently in the midst of the longest streak ever recorded without an intense hurricane landfall 
Because the time period with reliable data at the global level on landfalls is short (42 years, including 2011), it will be exceedingly difficult to develop theoretical explanations of the observed variations beyond simple randomness. Consider that 1971 was a strong La Niña year and had 32 landfalls and 2011 was also a La Niña year and had only 11.
If you are interested in overall trends in tropical cyclones, and not just the ones making landfall, you should have a look at Ryan Maue's excellent tropical cyclone page, where you can find the above image of overall global tropical cyclone activity since 1978.

We'll post up the paper and all of the underlying data as soon as it is available from JOC.

Postscript: Regular readers will remember this paper from last fall as one which, after the reviews came in, an editor at Geophysical Research Letters bizarrely refused to discuss them with me. That water is under the bridge. However, thanks to the airing of that debacle the paper received various useful comments from colleagues, including those from Ryan Maue that were so significant that we invited him to join in as a co-author, leading to a rich new collaboration and an improved final product. Score one for the blogosphere in helping to make connections which ultimately improved the science published in the peer-reviewed literature.

7 comments:

  1. OK - another typically stupid question:

    Is a "landfall" of global tropical cyclones necessarily proportional to the metric of total global tropical cyclones - given that only 30% of the surface is covered by land?

    In other words, are the past landfalls of global tropical cyclones necessarily some 30% (or more, or less, if there is more, or less, land relative to water in areas prone to tropical cyclones) of the total # of past global tropical cyclones?

    Could there be a growth, or lack thereof, in total global tropical cyclones that is not in direct proportion to global tropical cyclone landfalls?

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  2. -1-Joshua

    Thanks ... Yes, a good question. Could TC patterns change such that landfalls are more or less likely? Sure. We see this on an annual basis with respect to the position of the Bermuda High in the North Atlantic (NATL).

    Could the climate change such that there are long-term secular changes in global landfalls vs. overall? Sure. Kerry Emanuel has made such an argument wrt the NATL (see my recent post on his paper). I don't think it is an easy argument to make at the global level (versus a single basin).

    However, hypothesizing such second-order effects won't make the detection or attribution problem any easier (quite the opposite). So I'd put it down as interesting speculation that cannot be resolved empirically in any easy way or short time period.

    Finally, I'd point out that the Maue graph at the bottom of the post is total TCs (lendfalling + others).

    Thanks!

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  3. If global temperatures have been rising since sometime in the 19th century should we have seen a pattern of change in TC's? I recall you posted the discussion of a model predicting future TC's as a result of GW.

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  4. -3-MIKE MCHENRY

    Thanks, Bender et al. suggest that under scenarios of human-caused climate change, detection of changes in TC behavior (in the NATL) will not occur until the second half of the current century:

    http://www.sciencemag.org/content/327/5964/454.abstract

    So the answer to your question is, not necessarily. Thanks!

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  5. Congratulations, well done. With regard to Joshua's question, would it not be true that pre-satellite era, landfalling TCs would likely be a more accurate metric since non-landfalling TCs, especially weaker ones, would be somewhat less likely to be reported thus skewing the trend?

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  6. I hope you've sent a copy to Dennis Hartmann and the other lead authors of WG1 Ch2 so that they can include it in IPCC AR5?

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  7. What would really be great if we got an independent statistical analysis of the IPCC 1.5C to 4.5C. The latest 2 papers in SCIENCE and NATURE seem to constrain the number to the low end of the range.

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