Operational Heatwave Products and Services of India Meteorological Department
Introduction
Heatwaves are among the most significant weather-related hazards affecting India. They pose serious risks to human health, agriculture, water resources, energy demand, and infrastructure. The impacts are particularly severe in densely populated urban areas, among outdoor workers, elderly people, children, and vulnerable communities.
The India Meteorological Department (IMD), under the Ministry of Earth Sciences, serves as the national authority for monitoring, forecasting, and issuing warnings related to heatwave conditions across the country. Through its extensive observational network, numerical weather prediction systems, and impact-based forecasting framework, IMD provides timely early warnings that support preparedness and response actions by disaster management agencies, health authorities, and other stakeholders.
This article provides an overview of heatwave definitions, monitoring methodologies, forecasting systems, and operational heatwave products issued by IMD.
What is a Heatwave?
A heatwave is a period of unusually high temperatures compared to the climatological conditions of a region. Since climatic conditions vary considerably across India, the temperature threshold used for declaring a heatwave also varies by region. According to IMD, heatwave conditions are considered only when the maximum temperature reaches:
- 40°C or more in plains,
- 37°C or more in coastal regions, and
- 30°C or more in hilly regions.
(i) Based on the Departure from Normal Temperature
| Category | Criteria |
| Heat Wave | Maximum temperature departure from normal between 4.5°C and 6.4°C |
| Severe Heat Wave | Maximum temperature departure from normal greater than 6.4°C |
(ii) Based on Actual Maximum Temperature
| Category | Criteria |
| Heat Wave | Maximum temperature ≥ 45°C |
| Severe Heat Wave | Maximum temperature ≥ 47°C |
These criteria enable a region-specific assessment of heat stress while accounting for local climatological conditions (Figure 1).
The actual-temperature criterion (≥45°C and ≥47°C) serves as an absolute heat-stress threshold. It ensures that extremely high temperatures are classified as heatwave conditions even when they are close to the climatological normal for traditionally hot regions such as parts of northwest and central India. Thus, IMD's definition combines both relative (departure from normal) and absolute (actual temperature) measures of heat stress.
Heatwave Monitoring by IMD
An effective heatwave warning begins with continuous monitoring of observed weather conditions (Figure 2).
IMD operates a nationwide observational network consisting of:
- Surface meteorological observatories
- Automatic Weather Stations (AWS)
- Automatic Rain Gauges (ARG)
- Upper-air observations
- Satellite observations
- Radar observations
These observations are used to monitor:
- Maximum temperature
- Minimum temperature
- Temperature departures from climatology
- Persistence of hot conditions
- Spatial extent of heatwave conditions
Daily monitoring allows IMD to identify emerging hotspots and track the evolution of heatwave conditions across different regions.
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Figure 2. IMD's nationwide observational network for monitoring weather and climate. The observing system integrates surface meteorological observatories, automatic weather stations, automatic rain gauges, upper-air observations, satellite remote sensing, Doppler weather radars, and other specialized observing platforms to provide continuous monitoring of atmospheric conditions across India. |
Operational Heatwave Forecasting Framework
IMD issues forecasts at multiple temporal scales to support preparedness and response activities (Figure 3).
1. Short-Range Forecasts (1–3 Days)
Short-range forecasts provide detailed district-level predictions of maximum temperature and heatwave conditions based on high-resolution numerical weather prediction models.
2. Medium-Range Forecasts (4–7 Days)
These forecasts provide advance information on the likely persistence, expansion, or weakening of heatwave conditions.
3. Extended-Range Forecasts (Week-1 and Week-2)
Extended-range outlooks provide guidance on temperature anomalies and potential heatwave conditions up to two weeks in advance, enabling preparedness planning at sectoral levels.
4. Seasonal Outlooks
Seasonal temperature outlooks provide probabilistic guidance on above-normal temperature conditions and the likelihood of heatwave-prone periods during the pre-monsoon season.
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Figure 3. Conceptual illustration of the multi-scale heatwave forecasting and early warning framework of the India Meteorological Department (IMD). Forecast guidance is provided across different time scales—seasonal outlooks, extended-range, medium-range, and short-range forecasts—to support strategic planning, preparedness, impact-based early warning, and timely response for reducing heat-related risks. |
IMD Heatwave Warning Products
IMD disseminates a range of operational products for different users.
Daily Heatwave Warnings
Issued by the National Weather Forecasting Centre and Regional Meteorological Centres, these warnings indicate:
- Areas likely to experience heatwave conditions
- Severity of heat stress
- Duration of expected conditions
- Associated impacts
Color-Coded Warning System
IMD uses an impact-based colour code system:
| Warning Level | Meaning |
| Green | No action required |
| Yellow | Be aware |
| Orange | Be prepared |
| Red | Take action |
The warning level reflects the expected intensity and societal impact of heatwave conditions.
Impact-Based Forecasts (IBF)
Impact-based forecasts translate meteorological forecasts into likely societal impacts and recommended actions. These forecasts help disaster managers and health agencies understand:
- Potential health impacts
- Risks to vulnerable populations
- Recommended preparedness measures
- Sector-specific advisories
Heatwave Guidance Portal
IMD maintains a dedicated heatwave information portal that provides:
- Heatwave definitions
- Daily heatwave maps
- Temperature anomaly maps
- Warning bulletins
- Public advisories
- Frequently Asked Questions (FAQ)
The portal serves as a centralized source of heatwave-related information for both users and the general public. The portal can be accessed at: https://mausam.imd.gov.in/responsive/heatwave_guidance.php
Heatwave Monitoring and Forecasting Products Available from IMD
IMD disseminates a suite of operational products that support heatwave preparedness, risk communication, and decision-making across multiple sectors. These products are available through IMD's operational websites, mobile applications, and forecast bulletins. The infographic of IMD's Heatwave Monitoring and Forecasting flowchain is given in Figure 4.
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Figure 4. Overview of IMD's operational heatwave monitoring and forecasting workflow. The system integrates nationwide weather observations, real-time monitoring, numerical weather prediction models, multi-scale forecast products, and impact-based warning dissemination to support timely preparedness and response by disaster management agencies, health authorities, and the public. |
1. Daily Heatwave Warning Bulletin
- District-wise heatwave forecasts for the next five days.
- Identification of heatwave and severe heatwave affected regions.
- Colour-coded warning levels (Yellow, Orange, and Red).
- Impact-based advisories and recommended actions.
2. Maximum Temperature Observed and Forecast Maps
- Daily forecasts of maximum temperature across India.
- Spatial depiction of temperature hotspots.
- Useful for identifying regions at risk of extreme heat.
3. Heatwave Warning Maps
- Geographic representation of heatwave risk.
- District-level warning categories.
- Easy interpretation for administrators and the general public.
4. Extended Range Temperature Outlooks
- Week-1 and Week-2 forecasts of temperature anomalies.
- Early indication of potential heatwave development.
- Supports preparedness planning by health and disaster management agencies.
5. Impact-Based Forecast (IBF) Products
- Translation of meteorological forecasts into potential impacts.
- Health-related risk information.
- Guidance for vulnerable populations and local authorities.
6. Heatwave Guidance and Public Awareness Material
- Heatwave definitions and warning criteria.
- Frequently Asked Questions (FAQs).
- Do's and Don'ts during heatwave conditions.
- Public awareness infographics and advisories.
Heatwave information is disseminated through:
- IMD Mausam website
- Mausam mobile application
- Meghdoot mobile application
- Social media platforms
- National and State Disaster Management Authorities
- Media outlets and public communication channels
Heatwaves and Public Health
Heatwaves can result in:
- Heat cramps
- Heat exhaustion
- Heat stroke
- Dehydration
- Increased mortality among vulnerable groups
The health impacts are often amplified by:
- High humidity
- Warm nights
- Prolonged duration of heatwave events
- Urban heat island effects
Recognizing these risks, IMD increasingly collaborates with health agencies, disaster management authorities, and local governments to support Heat Action Plans and Heat-Health Early Warning Systems.
As heatwave frequency and intensity continue to increase under a warming climate, the need for robust early warning systems becomes even more critical. Future advancements are expected in:
- Impact-based forecasting
- Heat-health risk forecasting
- Urban heat monitoring
- Sub-district level warning services
- Integrated climate and health information systems
- Multi-hazard early warning systems
Conclusion
Heatwaves are a major climate and public health challenge in India. Through continuous monitoring, multi-scale forecasting, impact-based warnings, and effective dissemination systems, IMD plays a crucial role in reducing heat-related risks across the country.
The evolution of heatwave services from temperature forecasting to impact-based early warning represents an important step toward protecting lives, supporting decision-making, and strengthening climate resilience in India.
Important Links for IMD Heatwave Products
1. IMD Heatwave Portal: https://mausam.imd.gov.in/responsive/heatwave_guidance.php
2. IMD Daily Impact-Based Heatwave Warning Bulletin
3. IMD Morning Heatwave Warning Bulletin
4. IMD Monthly Heat Wave And Temperature Outlook
5. IMD Seasonal Forecast Outlook
6. IMD Heat Wave Annual Report
7. IMD District-wise Heatwave Warnings
8. IMD FAQ on Heatwave
9. NDMA Heatwave Guidance and Advisories: https://www.ndma.gov.in/Natural-Hazards/Heat-Wave
Disclaimer: The views and interpretations presented in this blog are solely those of the author and are intended for educational and science communication purposes. They do not necessarily represent the official views, policies, forecasts, or positions of the India Meteorological Department (IMD) or any other organization with which the author is affiliated.
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