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 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 from 1900 to 2010, SST has increased by approximately 1.2OC thank to the result of global warming (there is 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 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 Figure 2: Total global storms and frequency, Source: justfact.com Source: Science, 2005 Examination of hurricane intensity (Figure 3) shows a substantial change in the intensity distribution of hurricanes globally The number of category 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 and is small also both in number and percentage In contrast, hurricanes in the strongest categories and 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 years from 2000 to 2003 there were storms while from 1969 to 1993 (25 years) there were only It’s unknown yet if the climate change has anything to 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 year 2005 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 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 References Robert Mendelsohn et al The impact of climate change on global tropical cyclone damage Nature Climate Change online, 2012, 2 Viet Nam Assessment Report on Climate Change Ha Noi : Institute of Strategy and Policy on natural resources and environment,, 2009 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 P J Webster et al Changes in Tropical Cyclone Number, Duration, and Intensity in a Warmer environment Science 2005, 309 Vũ Thanh Hằng, Ngô Thị Thanh Hương, Phan Văn Tân Đặc điểm hoạt động bão vùng biển gần bờ Việt Nam giai đoạn 1945-2007 Tạp chí Khoa học ĐHQGHN, Khoa học Tự nhiên Công nghệ 2010, Vol 26, 3S Trenberth, Kevin Uncertainty in Hurricanes and Global Warming Science 2005, 308 R A Pielke JR, C Landsea, M Mayfield, J Laver, and R Pasch Hurricanes and Global warming s.l : American Meterological Society, 2005 Mat collins et al The impact of global warming on the tropical Pacific ocean and el niño Nature Geoscience 2010 Ưu, Đinh Văn Sự biến động hoạt động đổ bão nhiệt đới vào bờ biển Việt Nam Tạp chí Khoa học ĐHQGHN, Khoa học Tự nhiên Công nghệ 2010, 3S