Southwest Monsoon, Chennai’s Unsung Hero – A COMK Long Term Rainfall Analysis

COMK Analysis

As humans many a time we take things for granted like some of those friends who are regularly by our side. Similarly many a times we tend to forgive the negatives from those we love like how we forget the silly shots played by flamboyant cricketers in the hope for the next innings to be expansive.

Weather bloggers of Chennai are no different we tend to fantasize about an excess Northeast Monsoon every year expecting cyclones, LPAs’ & Depressions to make a beeline towards Chennai Coast ignoring Southwest Monsoon as just bunch of thunderstorm activity. While the overall objective of this COMK study was to understand long term changes if any to rainfall pattern in Chennai we also wanted to understand some of the key aspects as well.

The Key Takeaways’ of the study are given below while the number crunching is given as a video. We have studied Chennai AP data since 1901. Ideally the study would have been complete if we could compare the Lake Areas data for the same period, in the absence of data we have studied a comparison for Chennai AP & Lake areas for 55 years between 1965 to 2019 long enough to show some patterns.

  • Over the last 100 years or so Chennai AP has been seeing an increase in overall rainfall with increase seen in both Northeast Monsoon & Southwest Monsoon season
  • In a worry the Lake Areas (Average Rainfall of Red Hills, Poondi & Cholavaram is seeing a reduction in Northeast Monsoon rainfall
  • Southwest Monsoon has been seeing an increase in rainfall over the past couple of decades with 4 out of the 10 highest rainfall seasons happening since 2000
  • Crucially City area seems to be getting more rains compared to Lake Areas. Is increased urbanization playing a role in changing rainfall pattern needs to be studied.
  • June and August the biggest contributors to the increase in Southwest Monsoon rainfall, with August seeing more than 30 cms rains many a times.
  • Northeast Monsoon is erratic without doubts though the comfort is the Decadal average since 2000 is hovering around 80 cms mark indicating a reduction in multiple / consecutive failures.
  • Only October is showing some sort of consistency over long term though 3 extreme episodes since 2000 may be giving us some hint.
  • November which is the “Make or Break NEM” month is too erratic to give comfort. 45 out of 119 years has seen Chennai AP record less than 20 cms
  • December is pretty much a Hit or Miss Month with 37 out of 119 years recording less than 5 cms of rainfall.
  • Southwest Monsoon is seen to be much more consistent with nearly 2/3rd of the years seeing better than expected rains if one were to compare it with NEM. The True Unsung Hero of Chennai Rains