Tiểu luận Impacts of Climate change on weather phenomena or on Socioeconomic activities.

G304 – Physical Meteorology and Climatology
Topic: Impacts of Climate change on weather phenomena or on Socio-economic
activities.
April 2013
Nguyễn Quang Văn
K55 TT KHMT
10000904


Impacts of Climate change on Tropical cyclones

Global Climate Change – commonly known as global warming and associated sea level
rise– is one of the most serious challenges facing the human beings in the 21st century.
Natural disasters and extreme climatic phenomena are increasing in number, affecting the
lives of humans across the globe.
During the 2004 hurricane season in the North Atlantic, an unprecedented four hurricanes
hit Florida; during the same season in the Pacific, 10 tropical cyclones or typhoons hit
Japan; “The biggest storms cause most of the damage,” said Robert Mendelsohn, the lead
economist on the project. “With the present climate, almost 93 percent of tropical cyclone
damage is caused by only 10 percent of the storms (1); Vietnam’s coastal areas bear the
brunt of tropical storms arising from the East Sea, with an average of almost 7 storms
yearly. It has been observed that tropical cyclone frequency has increased by 2.15 events
per 50 years, and the sea level has risen between 20cm per 50 years (2). Etc.
This article will focus on the impact of a warmer environment on cyclonic storms’ –
tropical cyclone - characteristics and their activities in the world and in Vietnam.
Tropical cyclones’ formation related to many factors including heat, moisture and
Coriolis force in order to create the cyclonic wind. The giant amount of water vapor was
supplied by the evaporation of warm sea water in between 20N and 20S latitude where
the average temperature is high enough (26 OC or higher). Thank to global warming these
conditions has changed, said in the negative direction, and lead to the change in cyclonic
storms in numbers, frequent, duration, intensity, and paths.

Since the 1970s, there has been an increase in both the intensity and existence time of
tropical cyclone in the Atlantic, in accordance with sea water temperature increase in the
tropical sea. The intensity of tropical cyclone tends to increase even in areas where both
the frequency and existence time of tropical cyclone tends to decrease.
Numerous studies have addressed the issue of changes in the global frequency and
intensity of hurricanes in the warming world. Our basic conceptual understanding of
storms suggests that there could be a relationship between its activity and sea surface
temperature (STT) (SST greater than 26OC is a requirement for tropical cyclone
formation in the current climate). As can be seen from the figure 1 from 1900 to 2010,
SST has increased by approximately 1.2OC thank to the result of global warming (there is
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a nonlinear upward trend in SSTs over the 20th century). STT also distributes different in
different regions (warmer near the equator). What differences could this possibly do to
the frequency of tropical cyclones? Researchers have done many experiments and the
results (3) show that a significant reduction in the frequency of tropical cyclones is
possible in response to the greenhouse gas-induced global warming. The most significant
decrease is indicated over the North Pacific. On the other hand, a considerable increase in
tropical cyclone frequency is indicated for the North Atlantic.

Figure 1: Sea surface temperature by decades

It has been found that the regional change in tropical cyclone frequency is closely related
to the distribution of the SST anomaly and the change in convective activity associated
with it. Over the regions where the SST anomaly is relatively small compared with
surrounding regions, even though it is positive, convective activity and tropical cyclone
frequency tend to decrease. This indicates that the climate of convective activity, and
tropical cyclone frequency distribution, depends on dynamical factors associated with the
SST distribution, rather than the thermodynamically factors associated with the change in

absolute value of local SST (3).
Tropical cyclones are classified in five categories (Saffir-Simpson scale) based on their
wind speed in which categories 1: 33-42m/s; 2: 43-49m/s; 3: 50-58m/s; 4: 58-70m/s; 5: ≥
70m/s. As mentioned before, although the frequency of storms tends to decrease (Figure
2), their intensity seems to be increase.

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Figure 2: Total global storms and frequency,

Source: justfact.com

Source: Science, 2005
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Examination of hurricane intensity (Figure 3) shows a substantial change in the intensity
distribution of hurricanes globally. The number of category 1 hurricanes has remained
approximately constant (Fig. 3A) but has decreased monotonically as a percentage of the
total number of hurricanes throughout the 35-year period (Fig. 3B). The trend of the sum
of hurricane categories 2 and 3 is small also both in number and percentage. In contrast,
hurricanes in the strongest categories 4 and 5 have almost doubled in number (50 per
pentad in the 1970s to near 90 per pentad during the past decade) and in proportion (from
around 20% to around 35% during the same period) (4).
There are many storms which have complex or “weird” tracks recently that can be name
such as Typhoon Nat, 1991; Hurricane Martha, 1969; Hurricane 12, 1975; Super
Typhoon Parma, 2003; Hurricane Kyle, 2002; Hurricane Ginger, 1971; Cyclone Rewa,
1993; Cyclone Steve, 2000; Hurricane Norbert, 1984; Typhoon Wayne, 1986. From these
10 storms we can see that the frequency of appearing the storms which has complex track

has risen. Over 4 years from 2000 to 2003 there were 3 storms while from 1969 to 1993
(25 years) there were only 7. It’s unknown yet if the climate change has anything to do
with this but technically climate change and global warming did make change in many
factors which includes those related to the storms.
As a peninsula country located in the tropical monsoon belt of Southeast Asia, Viet Nam
his one of the nations with a high potential of being most negatively impacted by climate
change. The country is already experiencing changes in fundamental climatic elements as
well as extreme weather phenomena such as storms, heavy rains, and droughts.
In the period from 1945 to 2007 Vietnam’s coastline saw an increase in the number of
tropical cyclone or typhoon mostly in the area of Da Nang-Binh Dinh, less in the area of
Ninh Thuan-Binh Thuan; storm season tend to be late and has shorter duration, Bac Bo
(Tokin) sea zone has more storm than Ninh Thuan-Binh Thuan and Nam Bo; frequency
of storm and depression seven sea zones near the coastline from 1945 to 1960 is less than
that from 1991 to 2000, extreme storms usually took place in between 1996 to 2000 (5).
These conclusions are somehow match with all the point above thus provides more
evidences for the impacts of global warming on tropical cyclone activities.
To aid more for the point of there are more and more weird storms as the global warming
increase, let considers an example: typhoon Kai Tak 2005 or storm number 8 year 2005.

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Experts concluded that this typhoon is the weirdest storm ever occurred in Vietnam. At
the beginning, it was just a depression with the intensity at level 6 in Beaufort scale, after
two days it reached level 12, first time in history (normally it took 3-4 days at least).

Source: internet
Not only the strength changed drastically but also the movement of the typhoon changed
far from usual. It took the path along the coastline from Da Nang to the not with a very
slow speed in compare with a level 12 powerful storm. After moving into Gulf of Tonkin

it end up by dropped from level 12 to a tropical depression.
In conclusion, climate change and global warming have result in the change of tropical
cyclone characteristics and activities which can be the increasing or decreasing in
frequency in different areas but both increases in intensity and complexion. In order to
mitigate any potential impacts of the disasters, these aspects should be foretold and the
ability to predict these aspects requires improved understanding and projections of
regional climate change but the key scientific question is not whether there is a trend in
hurricane numbers and tracks, but rather how hurricanes are changing.

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References
1. Robert Mendelsohn et al. The impact of climate change on global tropical cyclone damage. Nature
Climate Change. online, 2012, 2.
2. Viet Nam Assessment Report on Climate Change. Ha Noi : Institute of Strategy and Policy on natural
resources and environment,, 2009.
3. Influence of the Global Warming on Tropical Cyclone Climatology. Masato Sugi, Akira Noda,
Nobuo Sato. Tokyo : Journal of the Meteorological Society of Japan, 2002, Vol. 80.
4. P. J. Webster et al. Changes in Tropical Cyclone Number, Duration, and Intensity in a Warmer
environment. Science. 2005, 309.
5. Vũ Thanh Hằng, Ngô Thị Thanh Hương, Phan Văn Tân. Đặc điểm hoạt động của bão ở vùng biển
gần bờ Việt Nam giai đoạn 1945-2007. Tạp chí Khoa học ĐHQGHN, Khoa học Tự nhiên và Công nghệ.
2010, Vol. 26, 3S.
6. Trenberth, Kevin. Uncertainty in Hurricanes and Global Warming. Science. 2005, 308.
7. R. A. Pielke JR, C. Landsea, M. Mayfield, J. Laver, and R. Pasch Hurricanes and Global warming.
s.l. : American Meterological Society, 2005.
8. Mat collins et al. The impact of global warming on the tropical Pacific ocean and el niño. Nature
Geoscience. 2010.
9. Ưu, Đinh Văn. Sự biến động hoạt động và đổ bộ của bão nhiệt đới vào bờ biển Việt Nam. Tạp chí

Khoa học ĐHQGHN, Khoa học Tự nhiên và Công nghệ. 2010, 3S.

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