Urban precipitation

• Why do urban areas experience higher rates of precipitation?(5-10% more)


  1. Pollution > urban air holds more condensation nuclei in the form of dust particulates > more clouds > more rainfall
  2. Warmer air > warmer air holds more moisture
• Characteristics of urban drainage:


  1. Higher precipitation
  2. Greater surface runoff > impermeable surfaces
  3. Less vegetation > decreased interception so less evapotranspiration rates to cool air and reduce humidity therefore more drainage needed
  4. Less soil > ground becomes saturated faster > water doesn't infiltrate
• How urban areas are designed to deal with precipitation:

  • Designed to shed water quickly > sloping roofs, smooth rounded gutters
  • Smooth storm sewer systems > act as high density drainage system > gathers speed and erosional power as travels underground