Summary of Information on Typhoons in 2005

2005-12-31

The number of typhoons in the year 2005 was 23, much smaller than the average number of 27. The number of typhoons making landfall on Japan was 3, which is nearly average (2.6). Generally speaking, this is not a year that the impact of typhoons was especially notable. The number of typhoons that passed near Okinawa is 8, which is slightly larger than the average number of 7, and this is because this year there are some typhoons that move through Sakishima Islands to Taiwan or China. In the following, significant typhoons of this year are reviewed. Typhoon 200514 (NABI) This typhoon moved across Okinawa and the western part of Japan, and brought heavy rain of more than 1300mm over the southeast part of Kyushu. Especially damaged area is in the mountainous area of Miyazaki, and the flooding of rivers washed away bridges at many places. Other significant points of this typhoon is that record-breaking heavy rains occurred at the southern part of Kanto area, leading to inundation at many places even when the area was more than 1000km away from the center of the typhoon, and this typhoon maintained its strong intensity in the south of Japan with its gigantic rounded eye.
In comparison to the rush of typhoons in 2004, this year is more or less an average year. In the last year, the typhoon rush was linked with the change of typhoon activity due to global warming, but from this year's activity, the last year may be interpreted as an anomalous year.

Hurricanes

On the other hand, the hottest topic of this year among worldwide tropical cyclones is hurricanes in the North Atlantic Basin. This year is no less than a record-breaking year, both in terms of the number and the intensity of hurricanes. Firstly, the number of named storms was 27, which is much larger than the previous record of 21, and just after we were amazed by having the historically first Greek-alphabet hurricane "Alpha", the name proceeded to as far as hurricane "Zeta." Secondly, a few strong hurricanes, such as Hurricane "Katrina," repeatedly attacked the United States and Central America, and this caused huge damage which may be once in tens of years. In particular, Hurricane Katrina, and the catastrophe after the hurricane around New Orleans gave a deep shock to the world. A large part of a big city was completely inundated, the flooding killed as many as 1300 people, and recovery from the disaster was very slow -- these facts revealed the surprisingly fragile infrastructure of the United States. Moreover, it was later discovered that a disaster of this scale was almost predicted in advance by related organizations, so questions about whether the precaution and recovery of the disaster was appropriate raised a nation-wide argument, including race issues, and this made President Bush to go back and forth several times between Washington and affected areas. Furthermore, this hurricane highly raised the price of oil because oil factories in the southern part of the United States was severely affected, so the American style of living dependent on cars was directly hit. This hurricane is nothing short of one that gave huge and complex impact on the whole country, or to the world.

Increase of Hurricane Frequency

Long-term observations in the Atlantic Basin suggest more worrying scenario - the hurricane activity in that region is actually becoming more active in these ten years or so. That is, the general trend of hurricane activity has entered into an active cycle in the Atlantic Basin, and very active level like this year may not be unusual in the coming years. On the contrary, the increasing trend has not been clearly observed in the Pacific Basin, and in recent years the activity is relatively stable, or seems to be slightly decreasing. What makes difference in these two basins? Meteorologists are investigating the reasons, but it is difficult to draw clear-cut explanations. Of particular interest is relationship between typhoon (hurricane) activity and global warming, but the validation of the hypothesis is difficult in reality. Even if it is true that the hurricane activity is intensifying in the Atlantic basin, that does not automatically lead to the conclusion that it is the effect of global warming. It has been known that hurricane activity shows multidecadal natural variation, and that variation may be influenced most by factors that have nothing to do with global warming. Simulation results by many organizations suggest that the number of typhoons decrease while the intensity of individual typhoons increase in a warming environment. This plausible prediction is still uncertain. In fact, the number and the intensity both increased in the Atlantic Basin this year. And the activity is relatively inactive in the Pacific Basin. These facts suggest that relationship between typhoon activity and global warming cannot be represented by simple rules.

Measurement of the Long-term Trend of Typhoon (Hurricane) Activity

What makes this issue even complicated is the problem of measuring the trend of typhoon (hurricane) activity. In fact, the statistics of the number and the intensity of typhoons are not so reliable. For example, past data may not be reliable when we did not have any meteorological satellites, and on the other hand, recent data may not reliable when we only have estimate based on Dvorak method but do not have any flight reconnaissance, lacking real observation data (in the Atlantic Basin, flight reconnaissance is still in operation, though). These points suggest that the trend cannot be computed by simply using past typhoon statistics, but should be computed by applying calibration on any kinds of bias introduced in the past statistics. Computing the trend of typhoon activity is thus a highly technical and complex issue. The high temperature of sea surface reinforces evaporation, leads to the more formation of clouds, and may increase the frequency of heavy rains. But whether clouds thus formed develop into a well-organized spiral cloud system like typhoons is another issue. The prediction of having more frequent heavy rains in a warming environment is probable, but the prediction of having less and more intense typhoons is much less probable. We still do not know in what kind of situation typhoons can be formed, and it may be too early to say that we know relationship between typhoons and global warming.

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