IMD Colour-Coded Weather Warnings: What Each Level Requires

The India Meteorological Department issues warnings using a four-colour system which appears in every weather bulletin and news report during significant events. The colours are widely recognised and frequently misinterpreted, because they are commonly assumed to describe rainfall quantity when in fact they describe expected impact and the response required.

The four levels

Impact, not merely quantity

This is the essential point. The colour assigned reflects the expected consequence of the forecast weather in the particular area, taking account of local vulnerability, existing conditions and the capacity of the area to absorb the event.

Consequently, identical rainfall may attract different warning levels in different places or at different times.

Antecedent conditions matter considerably. Saturated ground produces greater runoff, and rivers already running high require less additional input to overtop their banks. A moderate rainfall event following a wet fortnight may pose greater danger than a heavier event following a dry one.

Rainfall terminology

Separately from the warning colours, the IMD uses defined categories to describe rainfall intensity in twenty-four hours, and these appear throughout its bulletins:

These describe measured or forecast quantity. The warning colour describes what that quantity is expected to do. Both appear in bulletins and they answer different questions.

Spatial terminology

Bulletins also describe how widely rainfall is expected across an area, and these terms are precisely defined:

• Isolated — up to 25 per cent of stations in the area
• Scattered — 26 to 50 per cent
• Fairly widespread — 51 to 75 per cent
• Widespread — 76 to 100 per cent

A forecast of isolated extremely heavy rainfall therefore indicates that most locations will see comparatively little, while a small number may see a great deal. This distinction is frequently lost in reporting, and it materially affects how the forecast should be acted upon.

Responding to each level

Yellow

The appropriate response is attentiveness rather than action. Check for updates, allow additional time for travel, and be aware that conditions may deteriorate. A yellow warning frequently precedes an upgrade if the situation develops.

Orange

Preparation is warranted. Consider whether travel is necessary, charge devices in anticipation of power interruption, secure loose items outdoors, and avoid low-lying areas prone to waterlogging. For those responsible for operations or events, orange is the level at which contingency arrangements should be activated rather than merely considered.

Red

Action is required. Avoid all non-essential travel. Follow instructions from local authorities without delay, particularly regarding evacuation. Keep away from rivers, streams and areas of known landslide risk. Red warnings are issued sparingly and should be treated with corresponding seriousness.

Practical guidance on interpretation

Warnings are area-specific. A warning applies to defined districts. A red warning for a neighbouring district does not necessarily apply where you are, and equally, an absence of warning for your district when neighbouring areas are under red merits attention rather than complacency.

Warnings are updated frequently. Levels change as forecasts develop. A warning issued in the morning may be revised by evening.

The absence of a warning is not a guarantee. Convective weather in particular can develop rapidly and locally. Localised flash flooding has occurred in areas under yellow warning.

Use official sources. The IMD publishes warnings through its national and regional centres, and the Mausam application. Social media summaries frequently omit the geographical qualification and the time validity, both of which are material to acting correctly upon the information.