Rainfall in West Siang
West Siang gets 69% of its rain from the monsoon, June to September, and July is its wettest month. In 2025 it got 2,878 mm, 6% above average (normal).
Month-wise rainfall in West Siang
Average rain in each month, 2006–2025.
| Month | Average rain | Share of the year |
|---|---|---|
| January | 16 mm | 1% |
| February | 43 mm | 2% |
| March | 79 mm | 3% |
| April | 229 mm | 8% |
| May | 307 mm | 11% |
| June | 517 mm | 19% |
| July | 545 mm | 20% |
| August | 445 mm | 16% |
| September | 357 mm | 13% |
| October | 148 mm | 5% |
| November | 16 mm | 1% |
| December | 9 mm | 0% |
Yearly rainfall in West Siang since 2006
Lighter bars are dry years, 20% or more below average (2009, 2011), when wells and borewells are drawn hardest. The last ten years averaged 22% more rain than the ten before.
What West Siang'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 West Siang sheds about 2,30,520 litres in an average year, most of it in four monsoon 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 West Siang?
About 2,712 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 2020 (3,939 mm) and the driest was 2009 (2,149 mm).
Which month gets the most rain in West Siang?
July, with 545 mm in an average year, followed by June and August. December is the driest month (9 mm).
How much of West Siang's rain falls in the monsoon?
69% of a normal year's rain falls from June to September. 8 months average 50 mm or more.
How much did it rain in West Siang in 2025?
2,878 mm, which is 6% above the 2006–2025 average, or "normal" in the India Meteorological Department's terms.
Is rainfall in West Siang increasing or decreasing?
The last 10 years averaged 22% more rain than the 10 before them. Year-to-year swings are still bigger than that change.
How much rainwater can a house in West Siang harvest?
A 100 m² (about 1,076 sq ft) concrete roof in West Siang sheds about 2,30,520 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 West Siang district. It reads close to, but not exactly the same as, India Meteorological Department rain-gauge totals, and rain varies within a district.