Rainfall in Kollam
Kollam gets 46% of its rain from the monsoon, June to September, and October is its wettest month. In 2025 it got 2,157 mm, 4% above average (normal).
Month-wise rainfall in Kollam
Average rain in each month, 2006–2025.
| Month | Average rain | Share of the year |
|---|---|---|
| January | 29 mm | 1% |
| February | 18 mm | 1% |
| March | 67 mm | 3% |
| April | 129 mm | 6% |
| May | 249 mm | 12% |
| June | 273 mm | 13% |
| July | 241 mm | 12% |
| August | 218 mm | 11% |
| September | 228 mm | 11% |
| October | 305 mm | 15% |
| November | 236 mm | 11% |
| December | 72 mm | 3% |
Yearly rainfall in Kollam since 2006
Lighter bars are dry years, 20% or more below average (2012, 2016), when wells and borewells are drawn hardest.
What Kollam's rain is worth to a building
Every millimetre of rain on a square metre of roof is a litre of water. A 100 m² roof in Kollam sheds about 1,75,525 litres in an average year, most of it in a few wet months. Sent into a recharge pit, it refills the ground instead of flooding the street.
Your building: how much can you recharge?
1 mm of rain on 1 m² is 1 litre. The surface factor allows for water lost to splash, evaporation and first-flush.
Frequently asked questions
What is the average annual rainfall in Kollam?
About 2,065 mm a year, averaged over 2006–2025 from NASA POWER satellite and weather-model data for the centre of the district. The wettest year in that time was 2021 (3,125 mm) and the driest was 2012 (1,327 mm).
Which month gets the most rain in Kollam?
October, with 305 mm in an average year, followed by June and May. February is the driest month (18 mm).
How much of Kollam's rain falls in the monsoon?
46% of a normal year's rain falls from June to September. 10 months average 50 mm or more.
How much did it rain in Kollam in 2025?
2,157 mm, which is 4% above the 2006–2025 average, or "normal" in the India Meteorological Department's terms.
Is rainfall in Kollam increasing or decreasing?
It has held roughly steady: the last 10 years averaged within 5% of the 10 before them. Year-to-year swings are much bigger than the trend.
How much rainwater can a house in Kollam harvest?
A 100 m² (about 1,076 sq ft) concrete roof in Kollam sheds about 1,75,525 litres in an average year: area × rainfall × 0.85 for splash and evaporation. Sent into a recharge pit, that refills the ground under the house instead of running into the drain.
Rainfall from NASA POWER (bias-corrected satellite and weather-model rainfall) at the centre of Kollam district. It reads close to, but not exactly the same as, India Meteorological Department rain-gauge totals, and rain varies within a district.