Karnataka is a province where the occurrence and distribution of rainfall is not uniform across the state. Karnataka receives mean annual rainfall of around 1355 millimetres. The state receives two monsoons: the North-East monsoon (October to December) and the South-West monsoon (June to September).
Average annual rainfall across Karnataka
Karnataka is divided into three meteorological zones, namely, Coastal Karnataka, North Interior Karnataka and South Interior Karnataka.
Coastal Karnataka is the region that receives heaviest rainfall in the state. It gets an average annual rainfall of 3,456 mm. South Interior Karnataka is a region that receives an average rainfall of 1286 mm, which is much less than what Coastal Karnataka receives. But it is not as dry as North Interior Karnataka which receives the least amount of rainfall in the state. North Interior Karnataka receives just 731 mm average rainfall annually.
Rainfall distribution throughout the year in Karnataka
Karnataka receives about 80% of the annual rainfall during the South-West monsoon period (June to September), 12% during the post-monsoon period (October to December), 7% during the summer season (March to May) and only 1% rainfall is received during the winter season (January to February).
Rainfall pattern across Karnataka
Rainfall distribution in Karnataka decreases as one moves from the western part of the state to the eastern areas. The Western Ghats and the coastal region of Karnataka receive mean annual rainfall of more than 4,000 mm. But as we approach the eastern parts of the state, the mean annual rainfall comes down to around 400 mm, showing the vast difference in the rainfall received across the state.
While the coastal region on the windward side of the Western Ghats gets 3,350 mm of rainfall during the southwest monsoon, on the leeward side of the Western Ghats the rainfall drastically declines to around 600-700 mm. This means the state experiences a gradual decrease in rainfall as one moves towards the West Coast.
Karnataka has two major rainfall deficit areas within its territory. Both these areas are situated in the North Interior Karnataka. One covers east Belgaum, Bijapur, the west Raichur districts and north-east Dharwad while the other covers east Bellary and Chitradurga district and a small region of Tumkur district. These two areas receive annual rainfall of 500-600 mm only. Challekere in the district of Chitradurga receives the lowest rainfall in the state with less than 500 mm annual rainfall.
The humid Malnad region enjoys an annual rainfall of 1,000-3,800 mm. But in the semi-arid regions of the state, the intensity of rainfall decreases considerably. In the central Dharwad district, a strip covering Chikmagalur, Arsikere, Kadur, Sira, Pavagada and, Hiriyur, northwest of Mysore district and adjoining Mandya district the rainfall is less than 140 mm.
Rainy season in Karnataka
In Karnataka the rainy season spreads over a period of four months (June to September) in the coastal areas, Western Ghats, Malnad areas and in Bidar district. In the maidan areas the rainfall spreads over a period of five to seven months.
The districts of Chitradurga, Hassan, Tumkur and Mysore enjoy the extended spell of rain spreading over five to seven months. The major part of Karnataka receives one-third of the annual rainfall during the months of September and October.
Average annual rainfall in the districts of Karnataka
Given below is the table that shows the average annual rainfall received by the various districts of Karnataka.
| District | Average annual rainfall (mm) |
|---|---|
| Bengaluru rural | 978 |
| Bengaluru urban | 885 |
| Chitradurga | 573 |
| Davanagere | 700 |
| Kolar | 744 |
| Shivamogga | 1,813 |
| Tumkuru | 688 |
| Bagalkote | 562 |
| Belagavi | 808 |
| Vijapura | 578 |
| Dharwad | 772 |
| Gadag | 612 |
| Haveri | 753 |
| Uttara Kannada | 2,835 |
| Bellary | 636 |
| Bidar | 847 |
| Gulbarga | 777 |
| Koppal | 572 |
| Raichur | 621 |
| Chamarajanagar | 751 |
| Chikmagaluru | 1,925 |
| Dakshina Kannada | 3,975 |
| Hassan | 1,031 |
| Kodagu | 2,718 |
| Mandya | 806 |
| Mysuru | 798 |
| Udupi | 4,119 |