El Niño can shift the odds of a wetter northeast monsoon, but it does not guarantee a Tamil Nadu flood. The video's historical comparison shows why seasonal averages and local flood events need separate explanations.
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Choose the right rainy season
The comparison concerns October, November, and December. These months cover the northeast-monsoon rainfall period used in the video.
The IMD normal is 442.8 millimetres for the Tamil Nadu, Puducherry and Karaikal meteorological subdivision. The narration rounds this to about 440 millimetres. Calling it Tamil Nadu alone loses part of the geographic scope.
A meteorological subdivision is an area that IMD uses for weather statistics. Its rainfall total does not describe each street or district separately.
Every season since 1950
The chart compares 1950 through 2025, which gives 76 years when both endpoints count. It combines historical IMD subdivision rainfall with later IMD Chennai reports.
The red bars identify El Niño seasons under the saved NOAA Oceanic Niño Index classification. This index describes temperature anomalies in a defined tropical-Pacific region.
The choice of index and seasonal classification matters. The graph uses the saved index series; it does not automatically update when an agency revises its data or method.
What the calculation shows
Recalculation of the saved official-source series gives a mean seasonal rainfall of about 438.9 millimetres across all 76 years. The 26 El Niño seasons average about 465.9 millimetres.
Dividing the El Niño mean by the overall mean gives about 1.061. Thus, those seasons receive about six percent more rain in this selected comparison.
Eighteen of the 26 El Niño seasons exceed the selected period's mean. “Above average” here means above about 438.9 millimetres. It does not mean above the separate 442.8-millimetre IMD normal in every case.
These are calculations from the saved dataset, rather than a new official IMD forecast. Different periods, classification choices, or reference values can change the comparison.
The 2015 example
The chart includes 2015, the year of the Chennai floods, as a strong El Niño season. Its subdivision total in the saved series is 665.3 millimetres.
That wet season is consistent with the video's proposed tendency. One matching example, however, cannot establish that El Niño guarantees a flood.
A flood also depends on where heavy rain concentrates and how water drains. A regional seasonal total does not measure either feature completely.
The exceptions
The saved series classifies 2002 as an El Niño season, yet records only 153.1 millimetres. This is about 35 percent of the 442.8-millimetre normal, close to one-third.
The same dataset records 782.3 millimetres in 2005, its wettest season in the longer series. It classifies that October-to-December period as La Niña.
La Niña is the cooler phase of the Pacific climate pattern. These exceptions show that the phase alone cannot determine the amount of northeast-monsoon rainfall.
A tendency, not a flood promise
The comparison supports a modest average difference within the chosen sample. It also shows wide variation between individual seasons.
The video's final outlook asks readers to use IMD's October-to-December forecast. That forecast concerns the coming season, while the historical chart explains past variation.
What this means
Use the historical result to understand a tendency. Use the current seasonal forecast and local heavy-rain warnings for planning.
FAQ
Which area does the rainfall normal cover?
It covers the Tamil Nadu, Puducherry and Karaikal meteorological subdivision.
Are the study mean and IMD normal identical?
No. They use different reference definitions, so their values and exceedance counts can differ.
Does a wet season prove that every district floods?
No. A seasonal subdivision total and a local flood measure different things.