Rainfall Pattern and Distribution of India

The National Picture

India’s average annual rainfall is roughly 118 cm. That single number hides huge regional differences.

The southwest monsoon itself splits into two branches. One is the Arabian Sea branch, the other the Bay of Bengal branch. They enter India from opposite sides, and meet over the northern plains.

The Four Rainfall Zones, and the Rain Shadow Effect

Geographers sort India’s rainfall into four zones, from very heavy to scanty. Very heavy means over 200 cm a year; scanty means under 50 cm.

• Very heavy (200 cm+): the Northeast and the windward slopes of the Western Ghats, where moist winds are forced upward.
• Moderate (100-200 cm): much of eastern and central India.
• Low (50-100 cm): the Deccan interior and the northwest plains.
• Scanty (under 50 cm): western Rajasthan, Kutch, and Ladakh.

Why does the Northeast get so wet? The funnel-shaped terrain around the Khasi Hills forces moist Bay of Bengal air upward, hard. Mawsynram and nearby Cherrapunji sit on a plateau shaped almost like a funnel. That shape squeezes incoming moist air into a narrow, intense uplift zone. On the other coast, the Western Ghats’ seaward face catches moisture straight off the Arabian Sea. That produces some of Peninsular India’s heaviest rainfall totals.

But cross to the far side of those same Ghats, and the story flips entirely. Moist winds rise and cool on the windward slope, dropping most of their moisture there. They then descend dry and warm on the leeward side. That’s a classic rain-shadow effect. It can drop rainfall by several hundred centimetres within just a few dozen kilometres, one of the sharpest local contrasts anywhere in India. The same mechanism, at a smaller scale, also explains drier pockets east of the Aravallis and inside the Deccan Plateau.

Scanty Zones, and Why

Not every dry zone is dry for the same reason.

• Western Rajasthan and Kutch: sit far from moisture-bearing winds, in the monsoon’s weakest reach.
• Ladakh: the towering Himalayas block monsoon moisture almost completely, creating a genuine cold desert.
• Kutch’s flat terrain: offers monsoon winds nothing to rise against, so moisture simply passes through without triggering much rain.
• Rajasthan’s weakened branch: the Arabian Sea monsoon branch crosses Gujarat and central India first. By the time it reaches western Rajasthan, it has already lost most of its moisture.

Variability, Not Just Averages

This spatial variability, not just seasonal timing, is why some Indian regions face chronic drought risk while others face annual floods. Low-rainfall regions also swing more year to year. A small shift in monsoon behaviour changes an already-small base figure by a large relative amount. Geographers measure this with the coefficient of variation. This statistic rises sharply as average rainfall falls, especially across India’s driest districts. A farmer in western Rajasthan can’t reliably plan around the long-term average. Any single year could differ from it sharply.

One Average, Many Realities

A single national rainfall average of 118 cm is nearly meaningless for planning. Farmers in Jaisalmer and Mawsynram face entirely different water realities, despite sharing one country-wide statistic. The same monsoon winds create both India’s wettest and driest places. What decides how much rain a place gets isn’t distance from the sea. It’s relief, and which way a slope faces the wind. A classic nearby example: Mahabaleshwar sits on the windward crest of the Western Ghats. It gets several times more rain than Pune, just a short distance away on the leeward side.

Zones Shape Agricultural Strategy

These four rainfall zones ripple out into decisions well beyond farming.

• Four zones, four farming strategies: scanty zones depend on irrigation. Very heavy zones manage excess water instead. This shapes cropping patterns more than soil type does.
• Reading drought and flood together: regional rainfall variability, not just the monsoon’s seasonal timing, is the key to reading India’s drought and flood maps as one connected picture.
• Groundwater planning: also depends heavily on this same zone map, since scanty zones must lean far more on aquifers than surface water alone.
• Dam design: reservoir capacity planning follows this same regional pattern, sized very differently for a scanty basin than for a very-heavy one.

2026 Monsoon Forecast: Below Normal

IMD’s second-stage forecast projected the 2026 southwest monsoon (June-September) at 90% of the Long Period Average. That placed the season in the “below normal” category. A developing El Niño was the main driver, with an 84% forecast probability of below-normal or lower rainfall nationwide. But even this forecast wasn’t uniform. Below-normal rainfall was expected over most of the country. Parts of the Northwest, Northeast, and eastern Peninsular India were still likely to see normal to above-normal rainfall. That’s the same zone-by-zone unevenness described above, playing out in a single real forecast year.