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Context

According to a CEEW study, 57% of Indian districts are at risk of excessive heat, which affects 76% of the population. Rising humidity and warm nights exacerbate the situation.

Heatwaves, Heat Stress, and Heat Risk

Concept	Details
Heatwaves	Prolonged periods of abnormally high temperatures in a specific region; no universal definition.
Heat Stress	Occurs when body temperature exceeds 37°C. Body struggles to release excess heat, leading to: - Discomfort - Cramps - Exhaustion If body temperature exceeds 40°C, it may cause heat stroke.




Heat Risk	As per CEEW, it refers to the probability of heat-related illness or death due to extreme temperatures.
Heat Risk Factors	1. Heat Intensity & Compounding Effects (e.g., humidity) 2. Degree of Exposure 3. Vulnerability of affected communities (age, health conditions, etc.)

Key Factors Increasing Heat Risk in India

Between 2012 and 2022, more than 70% of Indian districts had five or more very warm nights per summer.
Warm evenings prevent the body from cooling down after a hot day, raising the risk of heat stroke and exacerbating noncommunicable disorders such as diabetes and hypertension.
The relative humidity of the Indo-Gangetic Plain increased from 30-40% (1982–2011) to 40-50% (2012–2022).
High humidity reduces sweating, which increases heat stress, especially when the body temperature surpasses 37°C.
Cities with dense populations, such as Mumbai and Delhi, endure higher levels of exposure.
Rapid urbanization in tier II and III cities has resulted in higher nighttime temperatures due to heat-absorbing concrete infrastructure.
The districts of Andhra Pradesh, Maharashtra, Haryana, Punjab, Chhattisgarh, Bihar, and Uttar Pradesh are particularly vulnerable.
A large proportion of the population is old, and chronic health issues such as diabetes and hypertension are common.

Heat Action Plan (HAPs)

There are considerable gaps in India's HAPs, with many lacking long-term measures to mitigate excessive heat.
The Sustainable Futures Collaborative's investigation found that existing plans were not being implemented effectively.
Such planning inadequacies may result in a rise in heat-related mortality as heat waves become more common and extreme.

Source: Indian Express

Practice Question:

Q. With reference to the increasing frequency of extreme heat events in India, consider the following statements:

Heatwaves are declared in India when the maximum temperature exceeds 40°C in the plains.
Extreme heat has a direct impact on agriculture, particularly the yield of wheat and rice.
The National Disaster Management Authority (NDMA) has issued guidelines for heatwave action plans in India.
Urban heat islands are primarily caused by industrial emissions alone.

Which of the statements given above is/are correct?

A) 1 and 2 only
B) 1, 2 and 3 only
C) 2 and 4 only
D) 1, 2, 3 and 4

Answer:

B) 1, 2 and 3 only

Explanation:

Statement 1: Correct. The India Meteorological Department (IMD) declares a heatwave when the temperature exceeds 40°C in the plains.
Statement 2: Correct. Heat stress significantly affects agricultural productivity, especially of wheat and rice crops.
Statement 3: Correct. NDMA has issued guidelines and encouraged states to implement heatwave action plans.
Statement 4: Incorrect. Urban heat islands are caused by multiple factors including concrete surfaces, lack of green cover, and heat absorption—not just industrial emissions.