What is heat index and why is it important to measure?

September 8, 2023
Posted by: OptimizeIAS Team
Category: DPN Topics

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What is heat index and why is it important to measure?

Subject: Geography

Section: Climatology

Context:

Iran recorded a scorching heat index of 70 degrees Celsius (°C) in the coastal part of the country in August, earlier in July 2023 Persian Gulf Airport reported a heat index of 66.7 °C.

Heat Index:

In 2024, India is scheduled to launch its own heat index to quantify the impact of heat on its population and generate impact-based heat wave alerts for specific locations.

Topic	Information
What is the heat index?	The heat index is the combination of air temperature and relative humidity, it is the measure of how hot it really feels when relative humidity is factored in with the actual air temperature.
Aim of the new index	To quantify the impact of heat on its population and generate impact-based heatwave alerts for specific locations.
Parameters to be used	Temperature, humidity, wind, and duration of exposure
Significance	The analysis will help generate heat hazard scores, which will be used as thresholds to issue impact-based heatwave alerts for specific locations.
Heat Waves in India	According to IMD data, there was a 24% increase in the number of heat waves during 2010-2019 compared to 2000-2009. Between 2000 and 2019, the mortality rate for tropical cyclones decreased by 94% whereas it increased by 62% for heat waves. Heat waves is not notified as a natural disaster at the national level in the country.
How IMD defines Heatwave in India?	Heat Wave need not be considered till maximum temperature of a station reachesatleast 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.
Impact of heat waves	Heat waves cause cramps, exhaustion, stress, heat stroke and very severe heat waves even lead to death. The elderly, children, and people with heart and respiratory problems, kidney diseases and psychiatric disorders are particularly affected. Extreme periods of high temperatures can lead to a significant reduction in crop yields and cause reproductive failure in many crops.

Heat Index Calculation:

Dr. Robert Steadman, a professor in the textiles and clothing department of Colorado State University, had published a complex formula to calculate heat index in 1979.
He considered an important factor- Dew point (14^oC), which is the temperature at which gas is transformed into a liquid state.
Humidex of Canada:

The U.S. National Weather Service (NWS) uses the following chart to determine heat index:

Why is it important to measure the heat index?

Hot air can hold more moisture than cold air.
Humidity is typically higher during heat waves — which is why the heat index at the time is usually higher than just the temperature.
High humidity can lead to heat stress.
Humans usually maintain a core temperature in the range of 36.1 to 37.2 °C.
When the body is unable to get rid of excess heat, the heart rate increases due to a rise in core temperature, leading to heat-related exhaustion and rashes, among other symptoms. It can also be fatal if not addressed promptly.
During high humidity, it is difficult to sweat and then for that sweat to evaporate because the air around is already saturated with moisture. This makes it difficult for the body to lose heat. That is why measuring the heat index is more important than just measuring the temperature.

For details of Heat waves follow: https://optimizeias.com/68-dead-in-ballia-amid-heatwave-how-high-temperatures-combined-with-high-humidity-can-be-fatal/