August 19, 2011

Western Pacific Hurricanes Declining?

Filed under: Climate Extremes, Hurricanes

As we move further into hurricane season, we remind you that hardly a week goes by without another article appearing in a major journal on the topic of climate change and hurricane activity. We have covered many of these articles in the past, but another three articles appeared recently in the scientific literature that we found especially interesting.

First off is a recent article published in Climate Dynamics by two scientists with the Australian Bureau of Meteorology; they note that the “work was partially supported by the Australian Climate Change Science Program, which is administered by the Department of Climate Change and Energy Efficiency.” We suspect that the “Department” heads were less than pleased with the results of the effort.

Callaghan and Power set out to develop a long record of landfalling hurricanes (tropical cyclones) for the east coast of Australia and they were able to extend the record back to 1872. Obviously, there were no satellites and aircraft flying in 1872, but there were people living all along the eastern coast of Australia. The authors cleverly made use of anything and everything that might contain information about tropical cyclones in the past. Their land-falling dates were based on “meteorological observations, sea-faring reports, peer-reviewed publications; Bureau of Meteorology publications, Monthly Climatological Bulletins and Monthly Weather Reviews, unpublished TC season reports, bounded operational analysis charts back to the 1890s stored in the National Archives, unpublished internal Bureau documents; publications by state and local governments; archives of several Queensland newspapers; newspaper clippings held by the Bureau of Meteorology; books describing land-falling TCs; information held by the Cairns and Townsville Historical Societies; a report to the QLD parliament (1918); and extensive unpublished information from the public including numerous damage photographs. Reports on storm surge, wave action and shipwreck data from an extensive Australian shipwreck data base” … you get the message.

The key figure is presented below (Figure 1), and from 1872 to 2010, there has been a decline in severe tropical cyclone landfalls! In their own words, the authors note “A downward trend of 0.0021 TCs/year since 1872/1873 is also apparent. The linear trend fell from approximately 0.45 TCs/year in the 1870s to approximately 0.17 TCs/year in recent years. This corresponds to a decline in land-fall frequency of approximately 60%.” To assess statistical significance of the trends, the authors used a Monte Carlo approach and found “Only 10% of the simulations had trends with magnitudes as large as the corresponding observed value, indicating that the observed trend is significant at the 90% level.” They conclude “We also showed that the frequency of severe land-falling tropical cyclones declined to low levels in recent decades.”


Figure 1. The number of severe tropical cyclone (TC) land-falls in each TC season from 1872/1873 to 2009/2010 inclusive. The corresponding linear trend of -0.0021 TCs/year is also shown. This represents a decline of approximately 60% over the full period (from Callaghan and Power, 2010)

Our second feature is published in the Journal of Geophysical Research by three scientists from Nanjing, China; their funding came from multiple grants from the National Science Foundation of China and one grant from the National Grand Fundamental Research Program of China. Song et al. note that three different datasets are typically used in the study of tropical cyclones (typhoons) in the western Pacific including datasets from the Joint Typhoon Warning Center (JTWC), the Regional Specialized Meteorological Center (RSMC) Tokyo, and the Shanghai Typhoon Institute (STI). Believe it or not, the same tropical cyclone can be recorded differently by these three organizations. The centers use different algorithms to estimate maximum sustained winds, different time periods to define maximum sustained winds (e.g., 1 minute, 2 minute, 10 minute averages), and different criteria to define different storm categories.

It can be a bit confusing, but here is the bottom line. The authors conclude “In the period 1977–2007, the annual variations of tropical storms and category 1 typhoons (TYs) are similar between these data sets, but there are great differences for category 2 and higher TYs. In the JTWC data set, the annual number of category 2–3 TYs and potential destructiveness both decreased, but increased in category 4–5 TYs.” The climate change alarmists probably enjoy learning that the especially large storms have increased according to the dataset used by the Joint Typhoon Warning Center. However, Soon et al. then note “However, the trends in the RSMC and STI data sets are opposite to those in the JTWC data set. The downward trend in categories 4–5 TY annual number and potential destructiveness is significant for RSMC and STI.” Is that not incredible? Over the same time period and same region, and during a time of aircraft and satellite reconnaissance, one dataset shows an increase in severe storms while two other datasets show a significant decrease??

Our third piece was published in the International Journal of Climatology by four scientists with the Korea Meteorological Administration which funded the research. Choi et al. examined the landfalling tropical cyclones that stuck Korea since 1951, and using the data from Tokyo’s Regional Specialized Meteorological Center, they calculated the “Accumulated Cyclone Energy” for each event. Their bottom line figure below shows the frequency of low-intensity storms (F-TDEC), the frequency of high-intensity storms (F-TSTY), accumulated cyclone energy of the high-intensity storms (ACE), and the total moving distance (TMD) of the storms. The figure (Figure 2) is a bit confusing at first glance, but the solid lines are the key. Note that for each of the four indices, the highest values occurred 50 years ago!


Figure 2. Decadal variation related to a KP landfalling TC activity. Indices in order from an upper-most side are the total TC frequency (F-TDEC), the TC frequency with intensity greater than tropical storm (F-TSTY), accumulated cyclone energy (ACE) of TC with intensity greater than tropical storm, and total moving distance (TMD) for the TC lifetime, respectively (from Choi et al., 2010).

These three studies provide even more evidence (as if any more is even required) that shows that claims that hurricane activity is increasing are completely at odds with a plethora of findings reporting on observations collected from throughout the world.

References:

Callaghan, J. and S.B. Power. 2010. Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century. Climate Dynamics, DOI 10.1007/s00382-010-0883-2.

Choi, K.-S. B.-J. Kim, D.-W. Kim, and H.-R. Byunb. 2010. Interdecadal variation of tropical cyclone making landfall over the Korean Peninsula. International Journal of Climatology, 30, 1472-1483.

Song, J.‐J., Y. Wang, and L. Wu. 2010. Trend discrepancies among three best track data sets of western North Pacific tropical cyclones. Journal of Geophysical Research, 115, D12128, doi:10.1029/2009JD013058.




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