Green, yellow, orange, red: what IMD's weather alert colours mean for you

When the India Meteorological Department (IMD) issues a weather warning, it attaches a colour. The colours tell people and local authorities how serious the expected impact is and how much they should prepare.

The four colours

• Green (no warning): No action needed.
• Yellow (be aware): Severe weather is possible. Stay updated and plan around it.
• Orange (be prepared): Severe weather is expected and could disrupt daily life, transport or power. Prepare to protect yourself and your property.
• Red (take action): Extremely severe weather is expected, with a risk to life and property. Follow instructions from local authorities.

The same colours are used for heatwaves, heavy rainfall, thunderstorms, cold waves and other hazards. IMD issues them for districts and subdivisions, so check the warning for where you are.

How IMD defines a heatwave

For the plains, IMD considers a heatwave when the maximum temperature is at least 40°C and is significantly above normal for that place, or when the temperature reaches 45°C or more regardless of the normal. For hilly regions, the threshold is lower, at 30°C. Coastal stations have their own criteria. IMD also forecasts "warm nights", which matter because the body gets no chance to cool down.

Staying safe in a heatwave

Advice from the National Disaster Management Authority and health authorities is consistent:

• Drink water often, even if you are not thirsty. ORS, lassi, lemon water and buttermilk help.
• Avoid going out in the hottest part of the day, especially from about noon to 3 pm.
• Wear light, loose, light-coloured cotton clothes and cover your head.
• Never leave children or pets in parked vehicles.
• Check on older neighbours, young children, outdoor workers and people with heart disease or other illnesses.

Know the warning signs

Heat exhaustion can show up as heavy sweating, weakness, dizziness, headache, nausea and muscle cramps. Move the person to a cool place, loosen clothing and give fluids.

Heat stroke is a medical emergency. Signs include a very high body temperature, confusion, slurred speech, hot and dry or flushed skin, and fainting. Call 108 or 112, move the person to shade, and cool them with water and fanning while you wait for help.

Rainfall warnings use the same colours

During the monsoon, the colour codes are applied to rainfall. IMD defines the categories by how much rain falls at a place in 24 hours:

• Heavy rain: 64.5 to 115.5 mm
• Very heavy rain: 115.6 to 204.4 mm
• Extremely heavy rain: 204.5 mm or more

An orange or red alert for "extremely heavy rain" means a serious risk of flooding, landslides in hilly areas, and waterlogging in cities. That is the time to avoid travel and stay away from rivers and drains.

"Feels like": heat and humidity together

Air temperature alone does not tell the full story. In humid coastal cities, sweat evaporates slowly, so the body cannot cool itself as well, and 36°C in Chennai or Mumbai can feel more dangerous than 40°C in dry Rajasthan. IMD has started publishing an experimental heat index that combines temperature and humidity, and many weather apps show a "feels like" figure. Pay attention to it.

Heat action plans

Many Indian cities and states now have heat action plans. Ahmedabad introduced one of the first in South Asia in 2013, after a deadly heatwave in 2010. These plans set out early warnings, cooling centres, changes to outdoor work hours, drinking water points, and preparation in hospitals. Check whether your city or district has one, and what it offers.

Outdoor workers and employers

Construction workers, delivery riders, farm labourers and traffic police face the highest risk. Several state governments issue orders during heatwaves shifting outdoor work away from the afternoon. Employers should provide shade, water and rest breaks, and watch for workers showing signs of heat illness.

Pets and animals

Keep water bowls filled and in the shade, walk dogs early in the morning or late in the evening, and never leave pets in a car. Putting out a shallow bowl of water for birds helps too.

Apps for official alerts

The Ministry of Earth Sciences offers free apps: Mausam for city forecasts and warnings, Meghdoot for farmers' crop and weather advisories, and Damini for lightning alerts, which warns users when lightning is likely nearby.

The same colour system is used in winter for cold waves and dense fog. A cold wave alert matters most for older people, young children and people without proper shelter. Keep warm in layers, avoid heating a closed room with coal or wood (carbon monoxide can kill), and check on neighbours who live alone.

Where to check alerts

IMD publishes district warnings on its website and through its Mausam app. Many state disaster management authorities also send alerts by SMS. For your own safety, rely on official sources rather than forwarded messages.