UNIT 17 HEAT AND COLD WAVES Structure 17.0 Learning Outcome 17.1 Introduction 17.2 Heat Wave and Cold Wave: Criteria f 7.3 Affected Regions 17.4 Causes and Impacts 17.4.1 Causes of Heat Wave 17.4.2 Causes of Cold Wave 17.4.3 Impacts 17.5 Prevention and Preparedness 17.5.1 Prevention 17.5.2 Preparedness: Advance Warnings 17.6 Rescue and Relief 17.7 Conclusion 17.8 Key Concepts 17.9 References and Further Reading 17.10 Activity 17.0 LEAWING OUTCOME ~fterstudying this Unit, you should be able to: m understand air temperature and other criteria associated with heat and cold waves; o leam about the regions susceptible io such events including the vulnerable areas in India; o discuss the causes and impacts af heat and cold waves; r explain the health hazards and other damages caused due to extreme tempe'ratures during heat and cold waves; and o describe preventive measures to minimise the sufferings. Natural disasters like cyclones, floods, droughts and avalanches are of meteorological origin, that is associated with the weather situation. They wc&ionally leapcatastrophic situations heaping untoldmisery over the affected areaslregions. There are other weather situations as well which, though not disastrous by themselves, could linger on and create hazardous or even disastrous weather causing severe health problems leading to loss of lives, damages to seasonal crops and other related miseries. Among these are lingering spells of heat and cold waves. In the forty years i.e. from 1936 to 1975, nearly 20,000 people were killed in the United States by the effects of heat. In the disastrous heat wave of 1980 more than 1,250 people died in one single 204 Utzderstnizcli~zg Natural Disasters year, and in 1901 the heat wave killed 9,508 people in the United States. In Australia, heat wave\ accounts for more deaths than any other natural disaster, During 1939, severe heat wave took toll of 438 lives in South Australia and 400 of these were from Victoria province alone. In India too, casualties are no less significant. In theyear 1988, the severe heat wave killed nearly 900 persons in the states of Madhya Pradesh and Rajasthan during the months of May and June. In 1998, the casualties were still higher and according to a report, nearly 1,300 persons died in the heat wave over different parts of the country. The casualties from cold waves are no less. In extra-tropical countries, considerable casualties are due to low temperatures during a cold wave. In India and other countries in tropical areas, prolonged exposure to cold temperatures causes a number of deaths every year. Reports indicate that in India more than 600 persons dieddue to cold waves in the winter of 2001-02; and during the first fortnight of January 1983 the death toll was 452 in the two States of Bihar and Uttar Pradesh. In such extreme temperature conditions, the worst affected are the economically weaker sections of the society who cannot afford to ensure protection against exposure to the extremes of weather, particularly the temperitures. Other victims are those who are in the susceptible age groups like the very young and the old or the infirm with fragile health conditions, chronic invalids and those with weight and alcoholic problems which for apparent reasons have little adaptability to extreme temperature variations. * 17.2 MEAT WAVE AND COLD WAVE: CRITERIA i) General Temperature conditions, which vary from extreme hot to chilly weather differ from place to place. In fact, people living at a place for long get acclimatized to the normal weathedclimate of that place/region. For instance, in the coldclimate region (extra tropical regions or high level stations), day temperature of more than 30° C may be a hot day for the locals whereas this temperature in the warm climate region may present the feeling of comfortable weather. In the equatorial and tropical regions, locals are accustomed to wandhot weather. Threshold temperature at which hot weather begins to cause discomfort and health problems for people in these regions is apparently much higher than. in the higher latitudes. Comfortable temperature range for inland and coastal stations of the same climate regimes may also differ substantially due to varying humidity levels and the wind flow. In these cases, it is the va-iationof effective temperature (which takes into account wind speed and humidity along with ambient air temperature) from the normal climatic conditions, instead of the ambient air temperature alone, which influences the comfort level and related health risks. Similarly, people ipold clilnate conditions are acclimatized to rather low temperatures and threshold values for cold yave cohitions in those regibns are much lower than for people living in warm climates. Thus, health relatedproblerns due to cold waves in the extra-tropical countries are different, compared to those in the tropics. Injuries due to extreme cold temperatuses and related problems are more common in the extratropics. Threshold values of prevailing air temperature and their departure froin normal for heat and cold wav&s,therefore, differ from one place to another and arepri~narilydependent on the following factors: e LocaI climatic conditions e Geographic and Topographic fe'eat~~resof the place Heat and Cold Waves 205 It should also be noted that heat wave is reckoned with reference to abnormal rise in the day temperature (the so called Maximum Temperature) whereas cold wave is reckoned with reference to an abno~~nalfall in the early morning temperature i.e. the Minimum Temperature. ii) Criteria in Extratropical Countries &at Wave In the extra tropical countries, heat wave is considered as the period of abnormally hot and dry . weather or when it is uncomfortably hot due to humidity. To be tenned heat wave, it should last atleast more than a day over the area. Howeve]; conventionally heat wave lastsfor several days to several weeks depending on the prevailing weather conditions. Cold Wave Weather fluctuations in the extra-tropical regions are rather rapid and related with fast movement of weather systems. Many a times, cold air Inass sweeps in rapidly in the rear of a weather disturbance, which causes the chill to be more effective. Criterion f'orcold wave includes not only the minimum temperature to which it may fall but also the rate of temperature fa11 within 24 hours. i iii) Criteria followed in India IndiaMeteorologicalDepartment uses a simple procedure to define heat and cold waves in relation with temperature departures from the nonnal day (Maximum) and night (Minimum) temperatures of the placelarea. Heat waves are termed as moderate or severe if the prevailing maxi~num temperatures are markedly C6-7O C) or 8O C or more above normal, respectively. In the same way, cold waves are tenned mode9 .ate or severe if the prevailing xninirnu~ntemperatures are markedly (6-7°C) below normal or Fall by 8OC or more below normal. This is now being revised to make tel-minologies more in confolmity with international practices by linking the temperature departures with local climatic conditions andco~nfoft.levelsinstead of basing them on temperature departure values alone. Concept of Hot Day and Cold Day has been also added to describe the temperature extremes which are rather border line cases prior to attaining heat and cold wave stage. - - --- 17.3 AFFECTED REGIONS Sorne regions are more susceptible than others due to the following factors: a Solar heating and radiative cooIing effects are more over the land than over the sea. F~~rthermore,land and sea breeze tend to inhibit these effects over the coasts and islands, Land locked areas are, therefore, more prone to the occurrence of extreme temperatures, e In the tropics, heat waves are rather common in the land-locked areas due to intense solar heating by the direct sun rays. a In the mid-latitudes, preferred regions for heat waves are where southwesterlylnorthwesterly winds bring willin tropical air to higher latitudes in n~~thernlso~rtliemhemisphere, In northern hemisphere, eastern parts of North America and east European countries experience such weather situations more frequently during the surn~nermonths. In the southern hemisphere, different parts of west and south Australiaexperience heat waves, which persist for number of weeks and account for more number of deaths than any other natural hazard there, Urban areas experience greater effects of heat wave th~u~the rural regions, Asphalt and concrete, used in abundance in urban areas, store heat longer and release it gradually during night, which produce signiticcantly higher day and ~~igl'lttime temperatures in urban weas. Built up large cities act as heat islands. -. .-- ..- 206 U/tder.~tandingNaturril Disasters e Cold waves are associated with the incursion of cold air-mass to warm places. It generally takes place in the rear of the passage of low pressure system which brings cold air from higher latitudes to regions of lower latitudes. o In India, heat and cold wave conditions are Inore frequent in the north, central and adjoining eastern parts of the countly. These occasionally extend southwards to Peninsular India. Heat waves occur in the coastal regions of the States of Orissa and AndhraPradesh on the east coast when the prevailing weather is hot and huinid under calm wind and cloudless sky conditions. CAUSES AND IMPACTS Heat and cold waves are caused by the extreme temperature, during the summer and winter months. 17.4.1 Causes of Heat Wave Progressive northwardsouthward march of the sun towards the tropic of cancer/capricorn (23O30' NIS latitude) brings summer season to the northernlsoutherrt hemisphere, respectively. As the associated solar heating progl-esses with it, land areas in the interior of the continents consistently experience high temperatures during the summer season.