heat

1. Heat Index
Shobhit Katiyar, Sc-D, IMD
India Meteorological Department
Mausam Bhavan, Lodi Road,
New Delhi-110 003

2. Heat Wave/Warm Night Criteria
 Heat wave Criteria for plain region
a. Based on Departure from Normal
• Max. temp. ≥ 40°C
 Heat Wave: Departure from normal is 4.5°C to 6.4°C
 Severe Heat Wave: Departure from normal is >6.4°C or more
b. Based on Actual Maximum Temperature
 Heat Wave: When actual maximum temperature ≥ 45°C
 Severe Heat Wave: When actual maximum temperature ≥47°C
 Criteria for describing Heat Wave for coastal stations: Actual max. temp ≥ 37°C
 Heat Wave: Departure from normal is 4.5°C to 6.4°C
 Severe Heat Wave: Departure from normal is >6.4°C or more
 Criteria for describing Heat Wave for Hill stations: Actual max. temp ≥ 30°C
 Heat Wave: Departure from normal is 4.5°C to 6.4°C
 Severe Heat Wave: Departure from normal is >6.4°C or more
 Warm Night: It should be considered only when max. temp. ≥ 40°C.
 Warm Night: Minimum temperature departure from normal is 4.5°C to 6.4°C
 Very Warm Night: Minimum temperature Departure from normal is >6.4°C or
more
If above criteria are met at least in 2 stations in a Meteorological sub-division for at
least two consecutive days and it declared on the second day.

3. Heat Wave Days in March Heat Wave Days in April
Heat Wave Days in May Heat Wave Days in June

4. Heat Index
 Heat index/Apparent temperature: Feel like temperature to the human
body when relative humidity is combined with the air temperature,
important for the human body's comfort.
 When the body gets too hot, it begins to sweat to cool itself off. If the
sweat/perspiration is not able to evaporate, the body cannot regulate
its temperature.
 Evaporation is a cooling process. When perspiration is evaporated off
the body, it effectively reduces the body's temperature. When the
atmospheric moisture content (i.e. relative humidity) is high, the rate
of evaporation from the body decreases.

5. Heat Index = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR -
6.83783 x 10-3T2 - 5.481717 x 10-2R2 + 1.22874 x 10-3T2R + 8.5282 x 10-
4TR2 - 1.99 x 10-6T2R2
T – Dry air temperature (F)
R - Relative humidity (percentage)
Heat index values are for shady locations. If you are
exposed to direct sunlight, the heat index value can be
increased by up to 15°F.

7. Heat index (Contd.)
• Heat index contains assumptions about the human body mass, height,
clothing, amount of physical activity, individual heat tolerance, sunlight
and exposure time, and the wind speed.
• It does not take into account heating from direct sunlight, physical activity
or cooling from wind.
• It does not take into account body shape, metabolism, level of hydration
or other physical conditions etc.
• Equation described is valid only if the temperature is 27 °C (81 °F) or
more and relative humidity threshold is 40%, below which a heat index
calculation will return a number equal to or lower than the air temperature
(a lower heat index is generally considered invalid), varies with
temperature and is not linear.

8. Heat index (Contd.)
• The heat index does not work well with extreme conditions,
like supersaturation of air-- when the air is more than 100% saturated
with water.
• Heat index was underestimating the severity of intense heat waves.
• Heat index include the unavailability of precise humidity data in many
geographical regions, the assumption that the person is healthy, and the
assumption that the person has easy access to water and shade.
 Besides the heat index, other measures of apparent temperature include
the humidex, the wet-bulb globe temperature (temp. wind. radiant heat
and RH) , "relative outdoor temperature", “misery index” and "Real Feel".

9. Spatial Patterns of Normal (March)

10. Spatial Patterns of Normal (April)

11. Spatial Patterns of Normal (May)

12. Spatial Patterns of Normal (June)

13. Monthly mean Wind Speed (Knots)

14. ERF: Heat Index

15. ERF: Heat Index

16. ERF: Heat Index

17. ERF: Heat Index

18. MME: Heat Index

19. Operational: Heat Index

20. Heat Wave: Impact Based Forecasting
For color coded Impact based forecast following parameters may be utilized:
a) Absolute Temperatures and their departures
b) Heat Index
c) Percentile Method
d) Heat Hazard

21. IMD’s requirement for Impact
based Forecasting (IBF) of
Heat Waves:-
• Multistakeholder team
having experts from
academia/research as well
as operational setup from
specific sector.
• Easy accessibility of data
from the sectors.
• The aim of the team would
be to devise methods and
threshold for targeted
region wise sector specific
impact based forecasting
services.
Heat Wave + Health.
Coordination by NDMA and
depending on priority following
tentative sector could be
considered.
Heat Wave + Agriculture.
Heat Wave + Forest Fire.
Heat Wave + Transport.
Heat Wave + Energy.
Heat Wave + ………..
IBF requires domain expertise
from the specific sector in
addition to meteorological
expertise. These teams could be
tapping this multisectoral
expertise in generating targeted
forecast and warning services.

22. 7-May-24
THANK YOU