Hong Kong Climate Change PDF

4 What is happening in Hong Kong? How has the climate of Hong Kong 4.1 changed in recent decades? 6 Is Hong Kong getting warmer? Figure 1 shows the annual m...

4 What is happening in Hong Kong? How has the climate of Hong Kong 4.1 changed in recent decades? 6 Is Hong Kong getting warmer? Figure 1 shows the annual mean temperature of Hong Kong from 1885–2020. 25.0 General trend 24.5 1885 – 2020 1991– 2020 24.0 23.5 Temperature (°C) 23.0 22.5 22.0 21.5 21.0 0 1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 2015 2020 Year Note: No data from 1940–46. Source: Hong Kong Observatory Figure 1 Annual mean temperature of Hong Kong, 1885–2020 1 Describe the general trend in annual mean temperature from 1885–2020. 2 Compare the general trends between 1885–2020 and 1991–2020. Has the change in annual mean temperature been getting faster or slower? How can you tell? The climate in Hong Kong has been changing over recent decades. There are changes in a number of weather and climatic elements such as air temperature, rainfall, cloud cover and wind speed. 44  What is happening in Hong Kong? 4 A Rising air temperature From the general trend in Figure 1, we learn that the annual mean temperature of Hong Kong has increased by about 1.7°C since 1885. Clearly, the climate of Hong Kong has been getting hotter. The rate of temperature increase has also become faster in recent decades. As Hong Kong becomes hotter, the number of hot nights and very hot days increases, whereas the number of cold days decreases (Figure 2). 30 25 Long-term temperature rise in Hong Kong (Cantonese only) 20 Number of days 15 10 Annual number of hot nights 5 Annual number of very hot days Annual number of cold days 0 1885–1914 1991– 2020 Year Note: 1 A hot night refers to a day with a minimum temperature of 28°C or above. 2 A very hot day refers to a day with a maximum temperature of 33°C or above. 3 A cold day refers to a day with a minimum temperature of 12°C or below. Source: Hong Kong Observatory Figure 2 Annual number of hot nights, very hot days and cold days in 1885–1914 and 1991–2020 Calculate the differences in the annual number of hot nights, very hot days and cold days in the two periods shown. Complete Table 1. Table 1 Number of hot nights Number of very hot days Number of cold days 1885–1914 0.5 1991–2020 23.5 Percentage change +4,600% Furthermore, it is predicted that annual mean temperature of Hong Kong will rise by 3–6°C by 2100. Our summers will become longer and hotter. By 2100, it is possible that there will be only three cold days. We may even lose our winters altogether. 45  4 What is happening in Hong Kong? B Changes in rainfall The following changes in the rainfall pattern of Hong Kong are being observed: annual rainfall has slightly increased; number of days with rainfall has decreased. This means that the intensity of rainfall has increased; days with heavy rainfall (i.e. over 30 mm of rainfall per hour) have increased; and extreme rainfall events (i.e. over 100 mm of rainfall per hour) have occurred more frequently. C Other changes There are other changes in the climate of Hong Kong (Figure 3). In general, cloud cover and the number of days with thunderstorms have increased. The wind speed in urban areas has decreased, while that in rural areas has remained more or less the same. Cloud cover Days with thunderstorms Wind speed in urban areas +1.1% +2.1 days –0.2 m/s per decade per decade per decade (1961– 2020) (1947– 2020) (1996–2015) Source: Hong Kong Observatory Figure 3 Other changes in the climate of Hong Kong Which of the following descriptions about the changes in the climate of Hong Kong are correct? Tick ‘✓’ the correct boxes. 1 Increasing number of very hot days 2 Decreasing number of cold days 3 Increasing amount of annual rainfall 4 Increasing number of days with rainfall 5 Lower chance of extreme rainfall events 6 Decreasing wind speed in urban areas 46 thunderstorm 雷暴  What is happening in Hong Kong? 4 What are the causes of the changing 4.2 climate in Hong Kong? A Global climate change In previous units, we have learned that the global average temperature has been increasing and the global precipitation pattern has changed. Hong Kong is obviously affected by these global trends. They lead to rising air temperatures and changes in the rainfall pattern of Hong Kong. B Urban development in Hong Kong 7 What type of area in Hong Kong is the hottest? Figure 4 shows the types of areas of five places in Hong Kong and their annual mean temperatures in 2020. Table 2 Ta Kwu Ling N (23.7°C) Annual mean Place Type of area temperature (°C) Sha Tin (24.1°C) Hottest Wong Tai Sin (24.3°C) Tsim Sha Tsui (24.4°C) Stanley (23.9°C) 0 9 km Coolest Type of area Urban Suburban Rural Source: Hong Kong Observatory Figure 4 1 Complete Table 2 by arranging the five places according to their annual mean temperatures in descending order. 2 Which type of area is associated with higher temperatures? Why? (Hint: Think about the difference in population and building density, as well as the trapping of heat.) The area is associated with higher temperatures. This is because the population and building density there are ( higher / lower ). The ground surface is mostly covered with ( concrete / vegetation ), while tall buildings block the flow of. Therefore, ( more / less ) heat is trapped. Stanley 赤柱 Ta Kwu Ling 打鼓嶺 concrete 混凝土 47  4 What is happening in Hong Kong? Since 1885, the annual mean temperature of Hong Kong has increased by about 1.7°C. Such change is higher than the world average of about 1°C. This is mainly due to rapid urban development in Hong Kong. As the population of Hong Kong increases, more rural areas are converted into urban areas (Figure 5). The clearing of trees, construction of more buildings and the increase in urban activities have caused the heat island effect in urban areas (Figure 6). The heat island effect, which refers to the higher temperature in urban areas than in the surrounding rural areas, has a great impact on local climate. Heat island effect Figure 5 Aerial photograph showing the urban development of rural land in Fanling Are the changes in Table 3 caused by global climate change or urban development in Hong Kong? Tick ‘✓’ the correct column. (Hint: You may choose both.) Table 3 Global climate Urban development Change change in Hong Kong 1 Increase in annual mean temperature 2 Increase in the number of days with heavy rainfall 3 Increase in the amount of cloud cover 4 Increase in the number of days with thunderstorms 5 Decrease in wind speed 48 heat island effect 熱島效應  What is happening in Hong Kong? 4 ① Clearing of trees ② Buildings ③ Urban activities Plants help lower the a Material Urban activities (e.g. air temperature by transpiration, Concrete buildings absorb conditioning and transport) but trees are often cut and retain more heat than produce heat and greenhouse to make way for urban the vegetation and soil in gases, leading to higher development rural areas temperatures b Height and density Tall and dense buildings in urban areas block wind flow. More heat is trapped Heat island effect More frequent heavy Higher temperature in urban areas than in the surrounding rain and thunderstorms rural areas Higher temperature Higher temperature in the urban area favours the formation of clouds and rain Temperature Lower temperature in the rural area Rural area Urban area Rural area Moisture from wet surface (e.g. sea and reservoir) Figure 6 How urban development changes the climate of Hong Kong transpiration 蒸騰 reservoir 水塘 49  4 What is happening in Hong Kong? changes of visibility in Hong Kong Visibility refers to the distance at which objects can be seen clearly. When there is heavy rain, fog, mist, snow, or when there are many tiny suspended particulates in the air, visibility is reduced. The annual total number of hours with reduced visibility in Hong Kong increased between 1970 and the early 2000s (Figures 7 and 8). But in the past two decades, the visibility in Hong Kong has significantly improved. Factories and vehicles in Hong Kong Due to strict pollution control measures and the Zhujiang Delta Region (ZDR) in the ZDR, highly polluting factories have emitted large amounts of air pollutants been moved away or closed down Hours 1,600 Increased Reduced rapidly quickly 1,200 800 Increased steadily 400 0 1970 1980 1990 2000 2010 2020 Year Source: Hong Kong Observatory Figure 7 Annual total number of hours with reduced visibility in Hong Kong Grey indicates urban area Guangzhou Foshan Dongguan Regular green patches indicate farmland areas Zh Shenzhen u Ji an Zhongshan g Ko u Hong Kong Northerly wind in winter Macau Figure 8 The north and north-west monsoons carried air pollutants to Hong Kong, leading to low visibility in the past 50 fog 霧 mist 薄霧 suspended particulate 懸浮粒子 Zhujiang Delta Region (ZDR) 珠江三角洲區域 Foshan 佛山 Guangzhou 廣州 Dongguan 東莞 Zhongshan 中山 Zhu Jiang Kou 珠江口 Shenzhen 深圳 Macau 澳門  What is happening in Hong Kong? 4 What are the possible effects of climate 4.3 change in Hong Kong? Similar to other parts of the world, climate change is likely to bring negative effects to Hong Kong (Figure 9). In particular, the mean sea level in Hong Kong is predicted to rise by about 1 metre by 2100. In addition to warmer temperatures and higher sea levels, extreme weather events in both Hong Kong and other places are likely to impact different aspects of our lives (Figure 9). Natural hazards Extreme rainfall and stronger typhoons Extreme weather events increase the risk of landslides, which may damage power lines, may damage buildings and structures interrupting the power supply Rising sea levels and stronger typhoons bring greater storm surges. Extreme weather They increase the risk of flooding events may interrupt in coastal areas, disrupting traffic and telecommunications people’s daily life Society and health Environment Rising sea levels may flood A reduction in food production Mai Po Nature Reserve, destroying in other parts of the world the wildlife habitats there may lead to higher prices of imported food in Hong Kong N Impacts of climate change in other parts of the world may lead to higher prices of imported products in Hong Kong 0 10 km Warmer seawater may cause coral bleaching in Sai Kung, affecting the marine habitat Higher temperatures increase the cases of heat stroke and the spread of dengue fever Source: Hong Kong Climate Change Report 2015, Environment Bureau Figure 9 Possible effects of climate change on Hong Kong telecommunications 電訊 Mai Po Nature Reserve 米埔自然保護區 51  4 What is happening in Hong Kong? 1 Name TWO possible effects brought by stronger typhoons in Hong Kong. 2 How does the impact of climate change in other parts of the world affect Hong Kong? thunderstorm 雷暴 46 heat island effect 熱島效應 48 transpiration 蒸騰 49 Complete Figure 10 to show the causes and possible impacts of climate change in Hong Kong. ( / ) air temperature ➔ ➔ ➔ ➔ ➔ ➔ Global climate change ( / ) rainfall and days with heavy rain ( / ) thunderstorms ( / ) in cloud cover ➔ ➔ ➔ ➔ effect ( / ) wind speed in urban areas Extreme rainfall and stronger bring higher risks of l Urban development in Hong Kong Rising levels and stronger Clearing of increase the risk of f Tall and d Extreme weather events disrupt the buildings made of supply and Higher prices of imported and products More urban activities More health problems, e.g. heat stroke Rising sea levels and warmer seawater destroy wildlife Figure 10 52