India Rainfall Intensity Map — IMD + CPHEEO Manual

Annual rainfall and design 1-hour intensity for any Indian city. Six tiers from Very Low (Thar desert < 400 mm/yr) to Extreme (Cherrapunji belt > 6,000 mm/yr). Drives stormwater capacity, roof drainage rate, and rainwater-harvesting potential.
12
very-low
21
low
112
moderate
34
high
18
very-high
0
extreme
Very Low · Arid · < 400 mm/yr
Low · Semi-arid · 400–800 mm/yr
Moderate · Subtropical · 800–1,500 mm/yr
High · Tropical wet · 1,500–3,000 mm/yr
Very High · Equatorial / coastal · 3,000–6,000 mm/yr
Extreme · World's wettest · > 6,000 mm/yr
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Click any spot on the map to drop a pin and get the estimated zone. Map data © OpenStreetMap contributors.

About rainfall design

Stormwater systems and roof drainage are sized for the design 1-hour intensity (mm/hr) at a chosen return period (typically 5-25 years for residential, 50-100 years for critical infrastructure). The CPHEEO Manual maps annual rainfall to design intensity via depth-duration-frequency curves.

Practical sizing rules

  • Roof drainage: 1 cm² of downpipe per 1 m² roof per 50 mm/hr design rate.
  • Stormwater drains: Manning's formula with runoff coefficient 0.7-0.9 (paved), 0.2-0.5 (green).
  • Rainwater harvesting: storage volume = 0.6 × annual rainfall × catchment area × runoff coeff.
  • Foundation: include groundwater rise from monsoon recharge in design water table.

Cross-references

Source IS / IRC / NBC standards

CPHEEO ManualStormwater + water-supply design — primary sourceIS 875 (Part 3)Wind loads — combine with cyclonic rainIS 456:2000Concrete durability — exposure includes wet-dry cycles

Related maps

Cyclone ZonesHigh rainfall + wind events — combined designGroundwater DepthAffects rainwater harvesting potentialWind SpeedWind-driven rain affects cladding design

Calculators & tools

Water Demand CalculatorCPHEEO LPCD calculationWTP SizingWater treatment plant capacityPipe SizingStorm + supply pipe diameter

Articles & guides

CE HandbookDesign aids for drainage + roof slope

Frequently asked questions

What is the design rainfall intensity in Mumbai?

Mumbai's design 1-hour intensity ~75-100 mm/hr (5-year return period). Annual ~2,200 mm. CPHEEO recommends 100 mm/hr for stormwater + 75-200 L/s/ha for sub-catchment design.

What is the wettest place in India?

Mawsynram (Meghalaya) holds the world's annual rainfall record at ~11,872 mm. Nearby Cherrapunji historically averaged ~11,000 mm/yr. Both are in the Khasi Hills, capturing southwest monsoon convergence. Design here is site-specific — outside standard codes.

How do I size rainwater harvesting?

Storage volume = 0.6 × annual rainfall (m) × catchment area (m²) × runoff coefficient (0.8 paved). E.g., 1,000 sqm roof in Mumbai (2.2 m rainfall): 0.6 × 2.2 × 1,000 × 0.8 = 1,056 m³ collectable annually. Storage usually 5-10% of this for monthly carryover.

Annual rainfall values are 1981-2020 IMD long-period averages. Climate variability, microclimate (urban heat island, coastal cooling), and topography (windward vs leeward) cause significant deviation. Use IMD station data for the nearest specific monitoring station for design.

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