Perceptions of severe weather warnings in Hong Kong

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1 Meteorol. Appl. 9, (2002) DOI: /S Perceptions of severe weather warnings in Hong Kong T F Wong and Y Y Yan, Department of Geography, Hong Kong Baptist University, Kowloon Tong, Hong Kong In this study 320 people in Hong Kong were interviewed to assess their understanding and perception of severe weather warnings. The majority of the respondents (72%) received warnings from mass media. Although 99.4% of the interviewees claimed they knew all the warning signals, results indicate that most of them have only a basic understanding of what they mean. The study revealed that the warnings often lack other important information, such as the time of issue, validity period and precautions to be taken. Only 31% of the respondents stated they would take precautions at the issue of warnings, although people aged over 60 tended to be well prepared for the onset of severe weather. Public education is necessary to promote people s understanding of the warnings and awareness of the risks of severe weather. 1. Introduction The Hong Kong Observatory issues public warnings for tropical cyclones, thunderstorms and rainstorms when these storms are imminent. The accurate and appropriate issue of these warnings is essential to protect the public. Once severe weather is detected, the Central Forecasting Office is responsible for administering the warnings. In 1999, 95 thunderstorm and 27 rainstorm warnings were issued (Hong Kong Observatory 2000). There is no information currently available regarding the effectiveness of these severe weather warnings and the level of preparedness in the community, although research on this has been conducted elsewhere. For example, people s knowledge and response to severe thunderstorm and tornado warnings issued by the US National Weather Service have been assessed in Ohio by Wilson (1995), in Alabama by Liu et al. (1996) and in Arkansas by Balluz et al. (2000). Haque (1997) has studied the impact of tropical cyclone warnings in Bangladesh. The objectives of this study are to examine people s understanding and perceptions of severe weather warn- Table 1. Classification of tropical cyclones. ings and to scrutinise the precautions they take upon hearing them. 2. Severe weather warnings in Hong Kong 2.1 Tropical cyclone warning signals Tropical cyclones are classified according to the recommendation of the World Meteorological Organization by their maximum sustained wind speed near the centre. In Hong Kong, the classification is defined in terms of wind speed averaged over a period of 10 minutes (Table 1). The numbered signal system geared to the warning of wind conditions was first introduced in 1917, and was revised in 1931, 1956 and Table 2 presents the amended tropical cyclone warning signals that have been used since Signal number 1, the standby signal, indicates preliminary precautions are desired. All necessary precautions, such as securing loose objects and clearing gutters and drains, are required when signal number 3 is hoisted. With signal number 8, all precautions including bolting windows and doors, fixing adhesive tapes to large windowpanes and finding shelter, should be completed. Signal number 9 or 10 indicates that everyone should stay indoors (Hong Kong Observatory 1997a). Classification Tropical depression Tropical storm Severe tropical storm Typhoon Maximum 10-minute mean wind speed near the centre Up to 62 km/h 63 to 87 km/h 88 to 117 km/h 118 km/h or more These symbols, together with the numbered signals, appear as graphics in the corner of TV screens for the duration of a tropical cyclone. The weather station at Cheung Chau, an outlying island south-west of Hong Kong, is the only location where the symbols are physically hoisted and lights displayed at night. 377

2 T F Wong and Y Y Yan Table 2. Tropical cyclone warnings. Signal Display Meaning of the signal Symbol Lights Stand By 1 White A tropical cyclone is centred within about White 800 kilometres of Hong Kong and may later White affect Hong Kong. Strong Wind 3 Strong wind expected or blowing, with a White sustained speed of km/h and gusts which mayexceed 110 km/h. White Gale or storm expected or blowing, with a NW Ly Gale or Storm 8NW sustained wind speed of km/h from the quarter indicated and gusts which may exceed 180 km/h. SW Ly Gale or Storm 8SW White White NE Ly Gale or Storm 8NE White White SE Ly Gale or Storm 8SE White Increasing Gale or storm is increasing or expected to Gale or Storm 9 increase significantly in strength. Hurricane 10 Red Hurricane force wind expected or blowing with sustained speed reaching upwards from Red 118 km/h and with gusts that may exceed 220 kmw/h Figure 1. Severe weather warning symbols: (a) thunderstorm warning, (b) rainstorm warning (b-1: amber rainstorm warning (rain cloud is amber in colour), b-2: red rainstorm warning (rain cloud is red in colour), b-3: black rainstorm warning (rain cloud is black in colour)) 378

3 2.2 Thunderstorm warnings Thunderstorm warnings (Figure 1(a)) are issued to give short-term notice (4 hours or less) of the likelihood of thunderstorms affecting any part of Hong Kong. Initial warning may be extended if the thunderstorm is likely to persist or affect other part of the territory. When the thunderstorm warning is issued, people should avoid trees or masts, and high and exposed places which are likely to be struck by lightning. People should not touch water pipes, wire fences or similar metal installations. People on boats should watch out for the approach of swell and waterspouts (Hong Kong Observatory 1997c). 2.3 Rainstorm warnings Rainstorms often bring serious road flooding and traffic disruption. Rainstorm warnings were first introduced in 1992 and the system was revised in 1998 to include three levels of warnings: amber, red and black (Figure 1(b)). The amber rainstorm warning indicates that heavy rain (exceeding 30 mm an hour) has fallen or is expected to fall generally over Hong Kong. The warning alerts the public to the likelihood of flooding in lowlying and poorly drained areas (Hong Kong Observatory 1997b). The red rainstorm warning indicates that heavy rain (exceeding 50 mm an hour) has fallen or is expected to fall generally over Hong Kong and is likely to continue. Serious road flooding and traffic congestion are likely to occur. The black rainstorm signal denotes that very heavy rain (exceeding 70 mm an hour) has fallen or is expected to fall over Hong Kong, and is likely to continue. It indicates major disruption and inclement weather (Hong Kong Observatory 1997b). When the red or black rainstorm signal is issued, people should stay indoors or take shelter. Employees working outdoors should stop working and take shelter. People may take refuge in special temporary shelters set up by the Home Affairs Department. Employers are advised not to require their employees to go to work unless prior agreement on work arrangements during rainstorms has been made. Students should stay at home (Hong Kong Observatory 1997b). 3. Methods Using questionnaires, face-to-face interviews were conducted at eight Mass Transit Railway stations. This method has some advantages. Unlike a mail survey, respondents who are visually impaired or illiterate are Perceptions of severe weather warnings in Hong Kong included (Dixon & Leach 1984). Also, the amount of missing information is often less than that obtained from a self-administered questionnaire where respondents may skip those questions which they believe are irrelevant to them (Skeskin 1985). Forty interviewees were randomly selected at each of the eight stations, and a total of 320 interviewees were surveyed. To investigate the effectiveness of the severe weather warnings, interviewees were asked about their understanding of the symbols and the warnings, and the medium by which they first heard the warnings. To assess the level of preparedness, interviewees were asked about the precautions they took on hearing the warning. One score was given for each correct answer of the understanding of the warnings. A total score was then obtained for each respondent. The higher the score, the better their knowledge. Similarly, a score was given for each precaution taken. The higher the total score, the better the respondent s preparedness. Regression analysis using dummy variables was utilised to investigate the relationships of age and education with level of preparedness. 4. Results and discussion Of the 320 interviewees, 151 (47.2%) were females and 169 (52.8%) were males. Regarding the education of the respondents, 45 (14%) had no formal education, 74 (23%) had primary education, 150 (47%) had high school education and 51 (16%) had college education. Table 3 shows the number of respondents in various age groups. Twenty-eight (9%) were below 15 years, 247 (77%) were in the range years, and 45 (14%) were over 60 years. The age demographics shown in Table 3 were good indicators of people s perception of the warnings. 4.1 Effectiveness of the severe weather warnings Of 320 interviewees, 231 (72%) received warnings from the mass media, including television and radio broadcasting and newspapers, 67 (21%) learned from friends and relatives, 16 (5%) and 3 (1%) got the warning from internet and telephone inquiry services offered by the Observatory respectively. Another 3 (1%) respondents Table 3. Number of respondents in various age groups. Age group Number Percentage Below Over

4 T F Wong and Y Y Yan obtained the warning from other sources, such as fax and telex services provided by the Hong Kong Observatory. The results indicate that television and radio broadcasting is the most common means by which people receive the warnings. The severe weather warnings are disseminated effectively through various channels. The Hong Kong Observatory offers different services including telephone enquiry, fax and telex. The Observatory also has an excellent website so that people can obtain current weather information online. A total of 318 (99.4%) respondents declared that they knew the severe warning signals, and only 2 (0.6%) stated that they did not know any of the signals. The maximum and minimum scores for the knowledge of the severe weather warnings were 6.00 and 0.00 respectively, with a mean of 3.78 and standard deviation of These findings reveal that some respondents were ignorant of the warnings. Table 4 presents the number of respondents who provided answers to questions on the knowledge of severe weather warnings. Only 6% provided correct answers on the amount of rain expected during a black rainstorm warning, and only 8% knew the wind speed expected when tropical cyclone signal number 8 is issued. Although 94% of the interviewees knew there were three levels of rainstorm warnings, only 14% recognised the symbol of the least severe level. These results indicate that people have a basic knowledge but not a thorough understanding of the warnings. Weather bulletins, which provide general descriptions of the current weather, information on severe weather and weather forecasts for the Hong Kong area are broadcast only a couple of times each day on television, although more frequently on radio. The severe warning symbols appear only as graphics at the corner of TV screens during severe weather events. Although these graphic symbols are effective in conveying essential information, other important information such as the time of issue, validity period and precautions to be taken are missing. These extra pieces of information are vital if the warnings are to be effective (Anon. 1993; Salter et al. 1993), The colour coding used in rainstorm warnings can cause misunderstanding and confusion. Most people are unclear whether amber or red signifies the greater threat. Education is important to improve the public s understanding of the warnings. 4.2 Level of preparedness Only 31% (98) of respondents stated they would take some precautions when hearing of a severe weather warning, while 69% (222) would take no precautions. The maximum and minimum scores for precaution taken were 3.00 and 0.00 respectively, with a mean of 0.42 and standard deviation of The findings indicate that the respondents, on average, take minimal precautions. Tables 5 and 6 show the demographic information and preparedness of the 98 respondents who would take some level of precaution. Females were more likely to take precautions than males, and older age groups tended to take more precautions than the others. Most respondents would stock up on food and groceries and check the windows, while only four respondents would take other precautions, such as securing loose objects, removing flower pots from balconies, or going to shelters. A significant positive relationship was discovered between the number of precautions taken and the respondents aged over 60 (r=0.560, r 2 =0.313, p=0.005). This result reveals that the elderly were well prepared. Since most of them live alone, a high level of preparedness is necessary to compensate for the lack of help during severe weather. The significant high level of preparedness by respondents who had no formal education or only primary education (r=0.381, r 2 =0.145, p=0.000) indicates that they were more concerned Table 4. Knowledge of severe weather warnings. 380 Correct answer Wrong answer No. % No. % How many categories are there in tropical cyclone warnings? How many categories are there in tropical cyclone warning signal No. 8? How far (in km) the tropical cyclone from Hong Kong will the tropical cyclone warning signal No. 1 be issued? What is the windspeed when tropical cyclone warning signal No. 8 is hoisted? How many levels are there in the rainstorm warning? Which is the most severe level in the rainstorm warnings? Which is the least severe level in the rainstorm warnings? How much rain has fallen or is expected to fall over Hong Kong at the black rainstorm warning?

5 Perceptions of severe weather warnings in Hong Kong Table 5. Sex, age and education of respondents who would take precautions. Sex Number Percent Age Number Percent Education Number Percent Male Below No formal education Primary High school College Over Subtotal Female Below No formal education Primary High school College Over Subtotal Total Table 6. Precautions taken by respondents. Precautions Sex Number Age Number Education Number Stock up food Male 24 (17.8) Below 15 2 (1.5) No formal education 25 (18.5) Female 57 (42.2) (7.4) Primary 25 (18.5) (18.5) High school 26 (19.4) (11.1) College 5 (3.7) Over (21.5) Check windows Male 22 (16.3) Below 15 1 (0.7) No formal education 19 (14.1) Female 21 (15.6) (5.2) Primary 11 (8.2) (3.0) High school 13 (9.6) (4.5) College Over (18.5) Prevent flooding Male 2 (1.5) Below 15 No formal education 5 (3.7) Female 5 (3.7) (0.7) Primary 1 (0.7) High school 1 (0.7) College Over 60 6 (4.5) Others Male 3 (2.2) Below 15 No formal education 2 (1.5) Female 1 (0.7) (0.7) Primary 1 (0.7) High school 1 (0.7) College Over 60 3 (2.2) Total 135 (100.0) 135 (100.0) 135 (100.0) about the risk of loss during severe weather than others. Their lower socio-economic status would probably cause this behaviour. These findings reveal that the majority of the public are not aware of the risks of severe weather. Public education is crucial in promoting public awareness. Schools should be targeted to incorporate these themes across the curriculum. Mass media should also help disseminate these notions. 5. Summary Most people in Hong Kong have only a basic understanding of severe weather warnings and appropriate responses to them. To help increase the effectiveness of the warnings, the time of issue and validity period as well as the warning symbol itself could be showed on TV. The low percentage (31%) of interviewees taking precautions at the issue of the warnings indicates that people are not aware of the risks of severe weather. Public education is necessary to improve people s understanding of the warnings and awareness of the risks of severe weather. Acknowledgements The authors would like to thank Dr John Harrington at Kansas State University and an anonymous referee for their valuable comments and suggestions. 381

6 T F Wong and Y Y Yan References Anon. (1993) Guidelines for effective warnings: towards improved severe weather and flooding warning effectiveness. Macedon Digest 8: Balluz, L., Schieve, L., Holmes, T., Kiezak, S. & Malilay, J. (2000) Predictors for people s response to tornado warning: Arkansas, 1 March Disaster 24: Dixon, C. J. & Leach, B. E. (1984) Survey Research in Underdeveloped Countries. Geo Books, Norwich, UK. Haque, C. E. (1997) Atmospheric hazards preparedness in Bangladesh: a study of warning, adjustments and recovery from the April 1991 cyclone. Natural Hazards 16: Hong Kong Observatory (1997a) Hong Kong s Tropical Cyclone Warning Signals. Government Print, Hong Kong. Hong Kong Observatory (1997b) Rainstorm Warnings. Government Print, Hong Kong. Hong Kong Observatory (1997c) Thunderstorm Warnings. Government Print, Hong Kong. Hong Kong Observatory (2000) The Year s Weather, Government Print, Hong Kong. Liu, S., Quenemoen, L. E., Malilay, J., Noji, E., Sinks, T. & Mendlein, J. (1996) Assessment of a severe weather warning system and disaster preparedness, Calhoun County, Alabama, American Journal of Public Health 86: Salter, J., Bally, J., Elliot, J. & Packham, D. (1993) Vulnerability and warnings. Macedon Digest 8: 1 7. Skeskin, I. M. (1985) Survey Research for Geographers. Association of American Geographers, Washington DC. Wilson, B. C. (1995) An analysis of the public knowledge and perception of the National Weather Service s severe thunderstorm and tornado watches and warnings in Ohio. Unpubl. MA thesis, Ohio University. 382

While all thunderstorms are dangerous, the National Weather Service (NWS) defines a severe thunderstorm as one that:

While all thunderstorms are dangerous, the National Weather Service (NWS) defines a severe thunderstorm as one that: Produces hail at least three-quarters of an inch in diameter. Has winds of 58 miles