IMD warning colours tell people how to respond to expected weather. The colour reflects possible impacts and likelihood, as well as the weather's expected strength.
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Read the colour as an instruction
The India Meteorological Department, or IMD, uses four colours. They provide a simple action message before you read the detailed forecast.
| Colour | Meaning |
|---|---|
| Green | No warning |
| Yellow | Be aware and remain updated |
| Orange | Prepare |
| Red | Take action |
The colours do not replace the bulletin's instructions. A red warning concerns action for a specified place and period. It does not describe every district in India at once.
Rainfall categories
IMD also uses categories for rainfall depth over 24 hours. The values describe how much rain falls during that interval.
| Category | Rainfall in 24 hours |
|---|---|
| Heavy | 64.5 to 115.5 millimetres |
| Very heavy | 115.6 to 204.4 millimetres |
| Extremely heavy | 204.5 millimetres or more |
The narration rounds the upper boundary of very heavy rain to about 204 millimetres. The table gives the full boundary values, so adjacent categories do not appear to overlap.
What millimetres mean on the ground
Rainfall depth lets us compare amounts without choosing a particular container size. Imagine rain spread evenly over a flat square metre, with no drainage or evaporation.
One millimetre over that area occupies one litre. Therefore, 115 millimetres corresponds to 115 litres per square metre. This is a volume calculation, not a prediction that all the water remains at that location.
Real water can enter soil, drain away, or arrive from nearby ground. Flooding therefore depends on more than the rain depth at one point.
Impact changes the warning
A warning also considers what the weather could do. The video names flooded roads, interrupted rail travel, and power failures as possible impacts.
Likelihood matters too. Forecasters assess both the expected weather and the consequences if it occurs. This is why a rainfall category and a warning colour are not interchangeable labels.
The same rainfall amount can affect places differently. Local conditions determine how water moves and what lies in its path.
Warnings can change
IMD provides weather warnings across a period extending up to five days in the service described. A later bulletin can change the colour as observations and predictions change.
An orange alert can therefore become red. It can also decrease if the expected hazard changes. A warning is a forecast message with a valid time, rather than a permanent label for a city.
What this means
- Check the warning's issue time and valid period.
- Find the district or area that it covers.
- Read the expected impacts and action instructions.
- Check for a newer bulletin before making a weather-related decision.
FAQ
Does red simply mean a large rainfall total?
No. Its action message is “take action,” and the warning also considers expected impacts.
Does yellow mean no warning?
No. Yellow asks you to remain aware. Green represents no warning in this colour scheme.
Does 115 millimetres mean 115 litres everywhere in a city?
It means that volume per square metre where that depth falls. Rainfall can vary across the city.