Rainfall Intensity Calculator
Professional rainfall intensity calculator supporting multiple international standards. Assess precipitation intensity, flood risks, and landslide hazards with adjustable parameters for terrain, drainage, and urbanization.
Classification Standard
Enter Rainfall Parameters
No calculation results
Enter rainfall parameters and click Calculate to see intensity analysis and risk assessment
About Rainfall Intensity Calculator
What is Rainfall Intensity?
Rainfall intensity measures the rate of precipitation, typically expressed in mm/h (millimeters per hour). It's a critical metric for flood forecasting, urban drainage design, agricultural planning, and disaster prevention. High rainfall intensity over short periods poses greater flood risks than the same precipitation amount spread over longer periods.
Why Rainfall Intensity Matters
- •Flood Risk Assessment: High intensity rainfall can rapidly overwhelm drainage systems, causing urban and river flooding within minutes to hours.
- •Infrastructure Design: Cities and agricultural areas must design drainage systems based on expected rainfall intensity to prevent property damage.
- •Disaster Preparedness: Intensity data enables early warning systems and emergency response coordination for extreme weather events.
- •Agricultural Management: Farmers use intensity forecasts to schedule irrigation, plan field operations, and protect crops from waterlogging.
How to Use This Calculator
Calculate rainfall intensity and assess associated risks in four simple steps.
Enter Precipitation Amount
Input the measured or forecasted precipitation in millimeters. Use actual measurements if rain has occurred, or forecast data from meteorological services for predictive analysis.
Specify Rainfall Duration
Enter the time period over which precipitation occurs in minutes. This is crucial for intensity calculation—the same amount of rain compressed into 30 minutes is twice as intense as rain spread over 60 minutes.
Select Optional Parameters
Choose advanced parameters (terrain type, drainage level, urbanization degree) to refine risk assessment. These factors significantly affect flood potential and water accumulation in different environments.
Analyze Results
The calculator provides rainfall intensity in multiple units, international standard classifications, flood/landslide risk levels, and specialized recommendations for meteorological, disaster prevention, urban planning, and agricultural applications.
Formula & Calculation Method
Core Calculation
Rainfall Intensity (mm/h) = Precipitation (mm) / Duration (hours)
Rainfall Intensity (mm/h) = Precipitation (mm) ÷ Duration (hours). For example, 60mm rain in 120 minutes = 60 ÷ 2 = 30 mm/h intensity.
Adjustment Factors Applied
- •Concentration Factor: 0-1 scale indicates rainfall distribution. 0.5 = uniform, 1.0 = concentrated bursts
- •Terrain Factor: Mountains (+15%), Urban (+10%), Suburban (+5%), Rural (0%) increase flood potential
- •Drainage Factor: Poor drainage (+20%), Moderate (+10%), Good (-5%), Excellent (-15%) water removal capability
- •Urbanization Factor: Built-up areas with impervious surfaces increase water accumulation (up to 20%)
WMO Intensity Classification Scale
- Very Light< 2.5 mm/h
- Light2.5 - 10 mm/h
- Moderate10 - 50 mm/h
- Heavy50 - 100 mm/h
- Very Heavy100 - 200 mm/h
- Extreme> 200 mm/h
International Rainfall Intensity Standards
Different countries and meteorological organizations classify rainfall intensity using different thresholds and categories. This calculator supports five major classification systems.
WMO (World Meteorological Organization)
International standard: Very Light (0-2.5), Light (2.5-10), Moderate (10-50), Heavy (50-100), Very Heavy (100-200), Extreme (>200) mm/h
China Meteorological Standard
Adapted for East Asian climate: Light Rain (0-2.5), Moderate (2.5-10), Heavy (10-25), Rainstorm (25-50), Severe Storm (50-100), Catastrophic (>100) mm/h
USA National Weather Service
Used by NOAA/NWS: Trace, Light (0.1-0.3 inches), Moderate (0.3-1 inch), Heavy (1-2 inches), Very Heavy (2-3 inches), Extreme (>3 inches) per hour
Japan Meteorological Agency
Japanese standard: Drizzle (0-1), Weak (1-10), Normal (10-20), Strong (20-50), Violent (50-80), Catastrophic (>80) mm/h
India Meteorological Department
South Asian standard: Light (0-2.5), Moderate (2.5-7.5), Heavy (7.5-35.5), Very Heavy (35.5-204), Extremely Heavy (204-408) mm/h
Frequently Asked Questions
Answers to common questions about rainfall intensity calculation and application.