Heatwave Trends, Causes And Solutions

Pranjal Pandey

Introduction:

Heatwave has no universal definition. In general, Heatwave refers to a prolonged period of excessively hot weather coupled with high humidity. Different countries have different definitions of heatwaves which is usually based on their population’s tolerance and average temperatures throughout their history. For example, In USA, common definition for heatwave is temperature above 33.2 degree Celsius (90-degree Fahrenheit) for a period of 3 days continuously whereas for Australia the definition for heatwave is temperature above 35 degrees Celsius for 5 days or 40 degrees Celsius for consecutive 3 days.

For India the definition for heatwave has been set by the Indian Meteorological Department (IMD)

Maximum temperature exceeding 40 degrees Celsius in plains
Maximum temperature exceeding 30 degrees Celsius in hilly regions
Temperature reaching 40 degrees Celsius in coastal areas

Under these scenarios a heatwave can be declared in India.

According to the World meteorological organization 2024 was considered to be the warmest year based on the 6 international datasets and 6 out of 10 warmest years on a 175-year scale have occurred in this decade itself (2015-2024).

IPCC (Intergovernmental Panel on Climate Change) has confirmed that human induced environmental distress has been a major factor behind climate vulnerability which would lead to unprecedented heat extremes in the future and most likely surpass the Paris agreement deadline of Average global temperature of 2 Degree Celsius above pre-industrial levels leading to glacial melting, ocean acidification, alterations or aberrations in biogeochemical cycles causing severe catastrophe such as soil disruption, drought, wildlife depletion, erratic rainfall patterns and most importantly increase in intensity and frequency of natural or man made disasters (riverine flooding, heatwaves, drought).

( Maximum and average temperatures along with climate index portray the current condition of heat extremes in urban cities, this data was recorded from the months of March to July.)

Trends:

In Asia, India is one of the most heatwave-vulnerable countries and could face events above survivable limits in the upcoming years. Between 1901 and 2018, India’s average temperatures have increased above 0.7 degree Celsius driven primarily by Greenhouse gas emissions. Based on CMIP5 climate model projections even if mean average temperature is limited to 2 degrees Celsius, the frequency of severe heatwaves could rise by 30 times of what we are facing right now. This could seriously impact crop productivity and increase the spread of vector borne diseases.

In 2024, India had endured one of its highest recorded heatwaves with temperatures soaring across several regions, for example Churu, Rajasthan where maximum daytime temperature was recorded to be 50.5 degree Celsius, parts of Delhi including Narela and Najafgarh approached 50 degrees Celsius and the national capital recorded its warmest night ever of 35.2 degree Celsius.

Heatwaves typically originate in northwest India or northern Pakistan and spread to adjoining regions. From March, temperatures rise sharply; the monsoon cools the east and south, but the northwest remains hot until late June-July. Most events occur in northwest and southeast India between April and June. Northwest India averages one 5-day heatwave per season, though durations can exceed a week.

(The average mean temperature currently stands at 0.74 Degrees, if we look closely at this chart, most of the highest temperatures are recorded within these two decades 2000-2010 and 2011-2020 and it continues to increase.)

Causes:

Natural Causes:

Persistent High-pressure systems:

High Pressure systems cause air to sink
Sinking air compresses and warms
Clouds get cleared
Excess solar radiation observed
Winds are weak which causes heat to be trapped thus heatwaves.

El-Nino:

Higher summer temperature
Delayed monsoon
Reduced Rainfall

La-Nina (Cooling phase after ENSO):

Brings wetter conditions
Improves heatwave conditions but does guarantee it (some regions still face problems.)

Anthropogenic Causes:

Climate Change: the most important factor behind heatwave, it increases the global baseline temperatures and increase the frequency and intensity of heatwaves.

Greenhouse Gas Emissions: Carbon Dioxide, Nitrous oxide and Methane are some of the greenhouses, they are emitted through fossil fuel combustions, industrial emissions or through domestic sources.

Urban Heat Island Effect: Common phenomena in urban settlements which occur due to excess concretization and lack of green cover leading to increasing in average mean temperatures in the region as compared to surrounding areas.

Deforestation/Industrial activities/Fossil Fuel consumption: these factors also heavily impact heatwave frequency and intensity and need to be closely assessed and monitored.

Policy Gaps:

To understand the gaps, we need to first know how the government prepares to mitigate heatwave, they propose heat action plans (HAPs), the exact number is unconfirmed but think-tanks estimate it to be above 100, the first proposed HAP was in Ahmedabad in 2013.

What is a HAP?

Heat Action Plans (HAPs) are guidance documents prepared by state, district, and city governments to help prepare for, respond to, and recover and learn from heatwaves. One of their most important functions is to direct scarce healthcare, financial, information, and infrastructural resources to those most vulnerable to extreme heat in that jurisdiction. This requires regular assessment of who is vulnerable and whether HAP interventions are reaching them.

Based on extensive research, here are the few key areas for improvement:

Most Heat Action Plans are not built according to the local requirements:

HAPs generally focus on dry extreme heat; only a few action plans seem to establish locally defined temperature thresholds though it is unclear whether they take local risk multipliers (such as humidity, hot nights, duration of continuous heat among others) into account to declare a heatwave. Hot nights, heatwaves coming earlier, and cascading impacts are unevenly considered across HAPs. Climate projections, which could help identify future planning needs, are not integrated into current HAPs. We recommend nuancing and localizing the heat hazard definition, including by incorporating climate projections.

Nearly all Heat action plans are poor at targeting vulnerable groups:

The primary role of HAP is to allocate scarce resources to the most vulnerable communities; without a proper assessment the resources may not be distributed properly sighting inefficiency in the implementation of the plan. Vulnerability assessments should be properly incorporated.

HAPs are severely underfunded:

Only some HAPs are properly funded, while most suffer bureaucratic hurdles and inconsistent resources, to attain better funding HAPs should be integrated in the national climate funding mechanisms or be considered as a disaster which would help harness disaster preparedness funds.

At present, India does not have a national repository for HAP where they could be regularly updated and centrally hosted, this brings lack of trust among the population and questions its transparency and commitment to mitigate the issue.

A national repository housed in NDMA (National Disaster Management Authority) should be hosted, where independent studies are conducted and reports are published which are made publicly accessible.

(This figure shows that not even half of the HAPs studied here are fulfilling their objectives.)

Conclusion:

Heatwaves have emerged as one of the most pressing climate related issues in India, with increasing frequency, intensity caused by natural and anthropogenic factors, its effects extend far beyond rise in temperature, it affects agriculture, reduces labor productivity, increased heat related illness and deaths, increases chances of drought, strains available water resources, severely damages ecosystem and effects wildlife. The need for heatwave adaption has become a matter of importance among countries and global organizations.

Indias has worked extensively on Heatwave mitigation by proposing Heat Action Plans with successful implementation in the district of Rajkot, drafting guidelines published by NDMA, early warning systems developed by IMD which use climate projections and models to predict extent of heatwave and thus determining it before-hand but limited resources and fragmented coordination has reduced the efficiency of mitigation.

To address these challenges we need proactive, evidence based and integrated public policy. Improving health surveillance, climate related heat resilience and proper infrastructure which suffices the needs of the present while keeping the demands of the future in consideration.

Sources:

Islam, S., Karipot, A., Bhawar, R., Sinha, P., Kedia, S., & Khare, M. (2024). Urban heat island effect in India: A review of current status, impact and mitigation strategies. Discover Cities, 1(1), 34. https://doi.org/10.1007/s44327-024-00033-3 (researchgate.net)

Dasgupta, R., Dasgupta, P., Dayal, V., Mishra, A., Murali, A., Sharma, G., & Pany, P. (2025). Heat action plans in eight Indian cities: Knowledge gaps & opportunities for intersectoral heat governance. Indian Journal of Medical Research, 162(3), 330–341. https://doi.org/10.25259/IJMR_1019_2025 (pubmed.ncbi.nlm.nih.gov)

DTE Staff. (2023, March 27). Most heat action plans in India are not suited to local contexts: Study. Down To Earth. https://www.downtoearth.org.in/climate-change/most-heat-action-plans-in-india-are-not-suited-to-local-contexts-study-88491 (downtoearth.org.in)

National Disaster Management Authority. (2019). National guidelines for preparation of action plan – Prevention and management of heat wave. Government of India. https://ndma.gov.in/heatwave (mausam.imd.gov.in)

Bhardwaj, S., Ravindra, K., & Mor, S. (2025). Heatwave research in India: Understanding current status, trends, and future directions. MAUSAM, 76(4), 1113–1130. https://doi.org/10.54302/mausam.v76i4.7187

Pillai, A. V., & Dalal, T. (2023). How is India adapting to heatwaves? An assessment of heat action plans with insights for transformative climate action. Centre for Policy Research.
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About the Contributor:

Pranjal Pandey is a student of environmental sciences at JSS AHER, Mysore His main objective from this fellowship is to contribute to evidence-based environmental policymaking by researching and evaluating policies that reduce the impacts of heatwaves in India.