Rain
How is Delhi's rainfall measured?
Delhi's rainfall is measured by IMD gauges, of which Safdarjung is the long-standing reference station for the city. Totals are reported against a seasonal normal — a long-period average, not a rule. The city has no legal rainfall threshold, so nothing here can be over a limit; the only honest comparison is with the normal, and the normal depends on the baseline period chosen.
One city, many gauges, one headline number
Delhi's rainfall is reported as though it were a single quantity. It is a reading at a point.
IMD maintains several gauges across Delhi. Safdarjung has the longest continuous record and is conventionally treated as the city's representative station, which is why a national bulletin's "Delhi recorded X mm" usually means Safdarjung recorded it.
Rainfall in a monsoon convective system varies over a few kilometres. It is entirely normal for one part of Delhi to record an extremely heavy day while another records almost nothing, and both numbers to be correct. A single headline figure for a 1,483 km² city conceals that by construction.
The seasonal total is then set against a normal. That comparison is where most of the confusion lives, because "normal" is an average over a chosen window and different windows give different verdicts on the same season.
- Safdarjung
- IMD's reference observatory for Delhi, and the source of most quoted city rainfall figures.
- Seasonal normal
- The long-period average rainfall for the season. A climatological reference, not a threshold.
- Departure
- How far a season ran above or below its normal, usually as a percentage. Meaningless without the baseline it was computed against.
There is no limit — only a normal
This band exists on every page in this section. On this subject it exists to say that the usual comparison is not available.
Legal limit on rainfall
No legal threshold.
No statute sets one
IMD heavy-rain threshold, 24 hours
64.5 mm
India Meteorological Department, day category
IMD extremely-heavy threshold, 24 hours
204.5 mm
India Meteorological Department, day category
A day category is the closest thing to a threshold that Indian rainfall has, and it classifies severity rather than permitting or forbidding anything. "Above normal" is not the same kind of statement as "above the standard", and this site does not colour it as though it were.
How to read a Delhi rainfall claim
Four things that have to be attached to the number.
Which gauge. Safdarjung, Palam, Lodhi Road and Ridge routinely disagree on the same day.
Which window. A 24-hour total ending at 8:30 am is IMD's convention, and it splits a night storm across two reporting days.
Which normal. State the baseline period, or the departure percentage cannot be checked.
Season or year. Delhi's rainfall is overwhelmingly monsoon rainfall; an annual figure and a June-to-September figure are close but not the same, and the difference matters in a year with heavy western disturbances.
What this number cannot tell you
- A city figure cannot describe the neighbourhood that flooded. That needs the gauge nearest to it.
- Rainfall cannot explain waterlogging on its own. Drainage, encroachment and land use decide what a given millimetre does.
- A single season above normal is not a trend, and a single season below it is not a drought.
- IMD rainfall figures are read by hand from published bulletins for this site. There is no open machine-readable feed, so this reading updates on a human cadence and says so.
Where this comes from
Every figure above is read out of one of these, at the address printed beside it.
- Rainfall statistics India Meteorological Department · Delhi's readings and its seasonal normal, read from published bulletins
- Hydromet division data supply portal India Meteorological Department · Where the longer station series are obtained
Reuse freely — CC BY 4.0. The grant covers this page. Each source above keeps its own terms, which is why every one of them is named.
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