A heat wave is defined as a prolonged period of excessively hot weather relative to normal temperatures for a region. The Indian Meteorological Department defines a heat wave as temperatures over 40°C in plains areas or over 30°C in hills for at least two days. Heat waves form due to high pressure systems trapping warm air and inhibiting convection, and have caused thousands of deaths from hyperthermia. The severe 2015 Indian heat wave was made worse by delayed monsoons and dry winds, resulting in over 2,500 deaths across several states.

2.  A heat wave is a prolonged period of excessively hot weather,
which may be accompanied by high humidity, especially in
oceanic climate countries. While definitions vary,a heat wave is
measured relative to the usual weather in the area and relative to
normal temperatures for the season.
 According to the IMD ,a Heat wave is qualified when air
temperature of at least 40 °C in the plains or greater than 30 °C
in the hilly region .For the IMD classification of heat waves ,temp.
Greater than 46 °C are considered & classified as severe heat
waves
 The term is applied both to hot weather variations and to
extraordinary spells of hot which may occur only once a century.
Severe heat waves have caused catastrophic crop failures,
thousands of deaths from hyperthermia, and widespread power
outages due to increased use of air conditioning.

3.  A definition based on Frich et al.'s Heat Wave Duration Index is
that a heat wave occurs when the daily maximum temperature
of more than five consecutive days exceeds the average
maximum temperature by 5 °C.
 In the Netherlands, a heat wave is defined as a period of at
least 5 consecutive days in which the maximum temperature
exceeds 25 °C (77 °F),
 In Denmark, a national heat wave (hedebølge) is defined as a
period of at least 3 consecutive days of which period the
average maximum temperature across more than fifty percent of
the country exceeds 28 °C (82.4 °F)
 In the United States, definitions also vary by region; however, a
heat wave is usually defined as a period of at least two or more
days of excessively hot weather

4.  A Heat Wave is a period of abnormally high
temperatures, more than the normal
maximum temperature that occurs during
the summer season in the North-Western
parts of India. Heat Waves typically occur
between March and June, and in some
rare cases even extend till July.
 The extreme temperatures and resultant
atmospheric conditions adversely affect
people living in these regions as they
cause physiological stress, sometimes
resulting in death.

5.  The Indian Meteorological Department (IMD) has given
the following criteria for Heat Waves :
 Heat Wave need not be considered till maximum
temperature of a station reaches atleast 40*C for
Plains and atleast 30*C for Hilly regions
 When normal maximum temperature of a station is
less than or equal to 40*C Heat Wave Departure from
normal is 5*C to 6*C Severe Heat Wave Departure
from normal is 7*C or more
 When normal maximum temperature of a station is
more than 40*C Heat Wave Departure from normal is
4*C to 5*C Severe Heat Wave Departure from normal
is 6*C or more
 When actual maximum temperature remains 45*C or
more irrespective of normal maximum temperature,
heat waves should be declared.

6.  Heat waves form when high pressure aloft (from
10,000–25,000 feet (3,000–7,600 metres)) strengthens
and remains over a region for several days up to
several weeks. This is common in summer (in both
Northern and Southern Hemispheres) as the jet stream
'follows the sun'.
 On the equator side of the jet stream, in the upper
layers of the atmosphere, is the high pressure area.
Summertime weather patterns are generally slower to
change than in winter. As a result, this upper level high
pressure also moves slowly. Under high pressure, the
air subsides (sinks) toward the surface, warming and
drying adiabatically.

9.  This warmer sinking air creates a high level
inversion that acts as a dome capping the
atmosphere, inhibiting convection, thereby
trapping high humidity warm air below it.
 Typically, convection is present along the
periphery of the cap where the pressure
becomes less. This peripheral convection,
however, can add to the high pressure dome
by ventilating the upper level outflow of the
thunderstorms into it.
 The end result is a continual build-up of heat
at the surface that people experience as a
heat wave

10.  May 2015,India was struck by a severe heat .Also 2017
experienced this too. Mainly heat wave occurred during Indian
summer ,which typically lasts from March to July.
 The heat wave was caused in large part by sparser pre-monsoon
seasons shower, which brought less moisture than normal to the
area , leaving large parts of India arid & dry.
 The sudden end of pre-monsoon rain shower an uncommon trend
in India has resulted into Heat Waves.
 Additionally ,the monsoon season is later and further south than the
normal trend. The weather pattern coupled with the El Nino Effect
which often increases temperature in Asia. The Loo , a dry wind
originating from Pakistan and northwest India ,has contributed to
increasing in temperature in India.
 Specially it affected AP,TS,ODISHA,BIHAR,WB.MP.2015 Heat
wave tolled 2500 deaths which also experienced the highest
temperature since 1995.

12. Effects of heat wave
 Health effects
 Mortality
 Underreporting and "Harvesting" effect
 Psychological and sociological effects
 Power outages
 Wildfires
 Physical damage

13.  https://en.wikipedia.org/wiki/Heat_wave
 https://www.climatecommunication.org
 http://www.ndma.gov.in
 http://www.firstpost.com/india/
 https://scijinks.gov/heat/
 http://www.planat.ch/en
 Indian Meteorological Department (IMD)