India's colour-coded weather warnings explained

The phone buzzes with "orange alert for your district". Is that a reason to cancel the journey, or just a routine bulletin? Many people know that red is worse than orange, but not what the colours are meant to make them do. This article explains the orange alert meaning, and the other three colours, using the India Meteorological Department's (IMD) own Standard Operation Procedure for Weather Forecasting and Warning (2021) [1].

(In Hindi: orange alert kya hota hai? It means "be prepared": a serious weather event is possible and the authorities and the public should get ready to act. The details follow.)

What do the four colours mean?

IMD uses four colours, and each one is paired with a word and an action. The procedure says the colour code mainly serves "as a signal for the disaster management authority about the impact of the weather expected so as to keep them ready for necessary action related to disaster risk reduction" [1]. The same four-level scale appears again in its chapters on warning products and on city forecasts [1].

So the orange alert meaning in IMD's scheme is a step up from "watch": it is the level at which district officials, utilities and the public are expected to prepare, not just stay informed. A red alert, in this table, is IMD's top level, labelled "Warning (take action)" [1].

Notice that the colour is about the action required, not only about how heavy the rain is. That is the idea behind impact-based forecasting, which we explain in impact-based forecasting and warnings.

How does IMD choose the colour?

IMD chooses the colour from two questions: how likely is the event, and how much damage would it do? The procedure says the colour for the 5-day forecast follows a matrix "giving thrust on the probability of occurrence of the event as well as its impact assessment" [1]. A high-impact event with a low probability and a moderate event that is almost certain can therefore both end up orange.

Probability comes from analysis of observations, model forecasts, including probabilistic outputs, and other diagnostic products. Impact is judged by the forecaster from past events, topography, land use, socio-economic factors and livelihoods, together with meteorological, hydrological and geophysical factors that interact with each other [1]. In other words, the same rainfall can earn different colours in different places, and a forecaster's judgement is part of the process.

Is the colour the same for a state, a subdivision and a district?

Not necessarily. The national forecasting centre issues warnings for meteorological subdivisions, while regional and state centres issue district-level warnings in tabular form [1]. The procedure says explicitly that the subdivision may be yellow while a district inside it is orange or red, depending on the expected weather and its impact [1]. If you live in a hill district, read the district table, not the state map.

What colour does heavy rain get?

For heavy rainfall, the procedure gives a guide table for district warnings. Its entries are [1]:

The words "isolated" and "scattered" are defined by how many stations record heavy rain in an area: isolated means 25 % or less, scattered 26-50 % [1]. "Heavy rainfall" itself means 64.5 to 115.5 mm in 24 hours, "very heavy" 115.6 to 204.4 mm, and "extremely heavy" 204.5 mm or more [1].

The procedure adds that these criteria are "of general nature". The meteorological centres are to adjust the colour for the location, the timing and any flood already under way [1]. This matters in a river catchment: heavy rain on already saturated ground and a swollen river is more dangerous than the same rain on dry ground.

Do the colours mean something different for thunderstorms?

Yes. For very short-range forecasts, called nowcasts (warnings for the next few hours; see nowcasting), IMD defines the colours directly by the weather expected [1]:

• Yellow: light rain below 5 mm an hour, light thunderstorm with gusts up to 40 km/h, or a low (below 30 %) chance of cloud-to-ground lightning.
• Orange: moderate rain of 5-15 mm an hour, moderate thunderstorm with gusts of 41-61 km/h, or a 30-60 % chance of cloud-to-ground lightning.
• Red: heavy rain above 15 mm an hour, severe thunderstorm with gusts of 62 km/h or more, thunderstorm with hail, or a lightning probability above 60 %.

So a nowcast turning orange to red within an hour is a real signal to move indoors, away from rivers and streams.

Watch, alert, warning: three stages for city rainfall

For heavy rain in major cities, IMD's impact-based service runs in four stages. A watch (advisory) comes 3 to 5 days ahead; an alert 1 to 3 days ahead; a warning 12 to 24 hours ahead, updated every 1 to 3 hours; and a final warning about 12 hours before the heaviest rain [1]. The colours track that progression. As the event nears and the confidence grows, the message moves from "be updated" to "be prepared" to "take action".

What should you do at each colour?

IMD gives the action word; the steps below are our practical reading of it, not IMD text:

1. Yellow: check the forecast twice a day; no change to plans is needed, but know the next update time.
2. Orange: prepare. Charge phones, review routes, avoid planning travel in hill areas or along rivers, and check that river and drain monitoring is working. Officials should review staffing, shelters and communication channels.
3. Red: act. Move people from low-lying and landslide-prone areas, stop non-essential travel, and follow instructions from the district authority.

Hill districts need extra care. Short, intense rain on steep catchments can raise a stream within minutes, as we explain in flash floods vs river floods.

A colour is a forecast, not an observation

The colour tells you what is expected. It does not tell you what the river is doing now. Upstream rain gauges and river level sensors show that, and an official danger level on a river gauge is a separate matter (see warning level vs danger level for river gauges). The two work best together: a forecast colour tells a district to prepare, and measured water level confirms whether the water is actually rising.

Key points

• IMD's four colours carry labels and actions: green (no warning, no action), yellow (watch, be updated), orange (alert, be prepared), red (warning, take action) [1].
• The colour comes from the probability of the event and its expected impact, not rainfall amount alone [1].
• A subdivision can be yellow while a district inside it is orange or red; read your district's warning [1].
• For heavy rain, existing flooding can raise the colour; for nowcasts, the colours are tied to rain, wind and lightning thresholds [1].
• A colour is a forecast. Observed rainfall and river levels show whether the event is actually happening.

Where ClimMaTech fits

A district-level orange or red tells you that heavy rain is likely, but not whether a particular stream is rising. At ClimMaTech we build river monitoring and warning systems that report measured water level and, where installed, flow. Our flood warning solution page describes how measured levels, thresholds and local alerts can be set up to sit alongside the official IMD warnings.

References

1. India Meteorological Department, Ministry of Earth Sciences, Standard Operation Procedure: Weather Forecasting and Warning, New Delhi, March 2021 (sections 1.7.8, 1.8, 4.8.1, 9.3.2). mausam.imd.gov.in