India, with approximately 1.35 billion people is the second most populous country in the world with considerably high levels of built-up area and population density. As per 2011 census, 31% of India’s population live in urban areas and 69% live in rural areas. The trend shows that the number of persons living in urban areas will continue to grow at a faster rate than the population in the rural areas due to migration and increasing urbanization. Increasing urbanisation and unique challenges associated with it such as Urban Heat Islands (UHI) effects in cities will further exacerbate the problem of heat wave in many parts of India.

The World Meteorological Organization (WMO) statements on global climate during 2011 and 2012 indicate that the global temperatures are continuing to increase. Heat-waves are projected to increase in number, intensity and duration over the most land area in the 21st century. This is directly affecting the communities, undermining their livelihoods through gradual, insidious changes in temperature and rainfall patterns, and resulting in increased frequency and intensity of hazards such as floods, cyclones, droughts, unseasonal rains and hailstorms, causing extensive damage to crops and agro-rural economy.


Heat Wave:

Heat wave is a condition when the abnormally maximum temperature in a region exceeds the normal maximum temperature, majorly in the northern India during the summer season. According to World Meteorological Organization (WMO), Heat wave is said to have occurred when the daily maximum temperature in a region exceeds the normal maximum temperature of that region by 5 degrees centigrade for 5 consecutive days.


The extreme temperatures combined with high humidity and resultant atmospheric conditions adversely affect people living in these regions leading to physiological stress, sometimes even death. This unusual and uncomfortable hot weather can impact human and animal health and also cause major disruption in community infrastructure such as power supply, public transport and other essential services. Heat wave is also called a “silent disaster” as it develops slowly and kills and injures humans and animals nationwide. Higher daily peak temperatures of longer duration and more intense heat waves are becoming increasingly frequent globally due to climate change. India too is feeling the impact of climate change in terms of increased instances of heat wave with each passing year.


Temperature Humidity Index:

There will be no harm to the human body if the environmental temperature remains at 37° C. Whenever the environmental temperature increases above 37° C, the human body starts gaining heat from the atmosphere. If humidity is high, a person can suffer from heat stress disorders even with the temperature at 37°C or 38°C. To calculate the effect of humidity the Heat Index Values are use. The Heat Index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. As an example, if the air temperature is 34°C and the relative humidity is 75%, the heat index--how hot it feels--is 49°C. The same effect is reached at just 31°C when the relative humidity is 100 %. The temperature vs humidity chart is placed and the temperature actually felt is placed below:


Heat wave in India:

Heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the pre-monsoon (April to June) summer season. Heat –waves typically occur between March to June, and in some rare cases even extend till July. Heat waves are more frequent over the Indo-Gangetic plains of India. On an average, 5-6 heat wave events occur every year over the northern parts of the country.

Annual mean land surface air temperature anomalies averaged over India for the period of 1991-2018 (Dotted line indicates the linear trend in the time series. The solid blue curve represents the sub decadal time scale variation smoothed with a binomial filter).

Source: National Guidelines for Preparation for Action Plan- Prevention and Management of Heat Wave

  Source: IMD Heat wave Death details

In recent years, heat wave casualties have increased. Abnormally high temperatures were observed during April –June during 2010 to 2015 across the country. In India the heat wave took 3028 lives in 1998 and more than 2000 lives in 2002. In Odisha, heat wave caused 2042 deaths in 1998 and more than 1200 deaths in 2002 in southern India. In India heat-wave caused 22562 deaths since 1992 to 2015 at various states


Heat wave Action Plan (HAP):



Heat Action Plan aims to provide a framework for the implementation, coordination, and evaluation of extreme heat response activities in different areas that reduce the negative health impacts of extreme heat. The Plan’s primary objective is to alert those populations most at risk of heatrelated illness that extreme heat conditions either exist or are imminent, and to take appropriate precautions. Extreme heat planning includes:

·         Identifying vulnerable populations and the health risks specific to each group;

·         Developing effective strategies, agency coordination, and response planning to shape a Heat Action Plan that addresses heat-health risks;

·         Implementing the Heat Action Plan and activating heat alerts; and

·         Evaluating and updating the Heat Action Plan regularly.


The Heat Action Plan aims to implement four key strategies:

1.     Building Public Awareness and Community Outreach to communicate the risks of heat waves and implement practices to prevent heat-related deaths and illnesses. Disseminating public messages on how to protect people against extreme heat through media outlets and informational materials such as pamphlets and advertisements on heat stress prevention. New efforts being launched include the use of modern media such as SMS, text messages, email, radio and mobile applications such as WhatsApp. Special efforts will be made to reach vulnerable populations through inter-personal communication as well as other outreach methods.

                                                               Colour Signal Chart

1.     Initiating an Early Warning System and Inter-Agency Coordination to alert residents of predicted high and extreme temperatures.


2.     Capacity Building Among Health Care Professionals to recognize and respond to heat-related illnesses, particularly during extreme heat events. Such trainings focus on primary medical officers and other paramedical staff, and community health staff so they can effectively prevent and manage heat-related cases so as to reduce mortality and morbidity.

1.     Reducing Heat Exposure and Promoting Adaptive Measures by launching new efforts including mapping of high-risk areas of the city, increasing outreach and communication on prevention methods, access to potable drinking water and cooling spaces during extreme heat days. Collaboration with non-governmental organizations is also identified as a means to expand outreach and communication with the city’s most at-risk communities.


Heat Wave conditions can result in physiological strain, which could even result in death. To minimize the impact during the heat wave and to prevent serious ailment or death because of heat stroke, all the departments / agencies shall take necessary timely action to implement the Heat Wave action plan.