South Asia monsoon — the complete guide to India, Pakistan and Bangladesh rainy season
The Indian monsoon affects 1.5 billion people. When it arrives, how it progresses, which cities are wettest, and what it means for daily life.
What is the Indian monsoon?
The Indian monsoon is the largest seasonal weather system on Earth, affecting over 1.5 billion people across South Asia. It is caused by the differential heating of the Indian subcontinent and the Indian Ocean: as the land heats faster than the ocean during summer, a massive low-pressure zone forms over northwestern India, drawing moisture-laden winds from the Indian Ocean northward. This creates the Southwest Monsoon, which delivers 70-90% of India's annual rainfall between June and September.
Monsoon onset and progression
The monsoon typically arrives at the Kerala coast around June 1st (±7 days) and advances northward in stages. It reaches Mumbai by June 10-15, Kolkata by mid-June, Delhi by late June/early July, and the Pakistan plains by early July. The monsoon "front" moves at roughly 100-200 km per day. IMD monitors the onset closely because a delayed monsoon means late planting and potential crop failure.
Regional rainfall distribution
Rainfall varies enormously across South Asia. Cherrapunji and Mawsynram in Meghalaya receive over 11,000 mm/year — among the wettest places on Earth. Mumbai averages 2,200 mm, concentrated in 4 months. Delhi gets only 800 mm. Rajasthan's Thar Desert receives under 200 mm. Pakistan's Sindh is similarly arid. Bangladesh, sitting in the Ganges-Brahmaputra delta, receives 2,000-3,000 mm and faces extreme flood risk.
Monsoon impact on daily life
The monsoon transforms South Asian life. Agriculture: 60% of India's farmland is rain-fed, making monsoon timing critical for food security. A weak monsoon can cause drought and food price inflation. Transport: Mumbai's local trains, carrying 7.5 million daily commuters, are frequently disrupted by flooding. Roads become impassable in many areas. Health: mosquito-borne diseases (dengue, malaria) surge during and after the monsoon. Economy: monsoon performance affects India's GDP by 0.5-1%.
Monsoon retreat
The monsoon withdraws from northwest India from September 1st and progressively retreats southward through October. The post-monsoon period (October-November) brings cyclone risk in the Bay of Bengal — some of the deadliest cyclones in history have struck during this period. The northeast monsoon (October-December) brings a second rainy season to Tamil Nadu and Sri Lanka's east coast.
Frequently Asked Questions
Is the monsoon getting more erratic due to climate change? ▾
Yes — studies show the monsoon is becoming more variable: longer dry spells punctuated by more intense rain events. The overall monsoon rainfall has not decreased significantly, but its distribution is changing — more flooding during heavy spells and more drought during breaks. This makes agriculture increasingly risky.
Can I visit India during monsoon? ▾
Absolutely — monsoon India is beautiful (lush green landscapes, waterfalls, fewer tourists) and culturally rich. Kerala backwaters, Rajasthan's desert lakes filling up, and the Western Ghats in full bloom are monsoon highlights. Pack rain gear and be flexible with your itinerary. Avoid Mumbai in July (peak flooding risk) and the Himalayan foothills (landslide risk).