Nature's Irrigation for Green Roofs

Nature's designs are always the most successful.

She knows when droughts come and rainfall is deficient, providing water vapor in the form of dew and fog for her plants.

Water vapor this am, no rain for days, Nature-based Irrigation

Designing green roofs and landscapes to avoid irrigation from potable water sources is important in today's world.

Success of a nature irrigated green roof depends heavily on sourcing a steady supply of water through rainfall, fog, dew and even frost. Using biomimicry based on Nature's plant designs design allows for important air water vapor collection.

Additionally, understanding the principles behind Nature's plant designs of water capture successes lie in an understanding of air humidity.  Humidity is the amount of water vapor in the air.  Humidity is an important source of irrigation for nature irrigated green roofs and is often present when rain is lacking.  Humidity is often described in terms of ‘relative humidity’ and ‘dew point’.

Relative humidity is the phrase commonly used by weather reporters to communicate the percentage as the amount of actual water vapor in the air divided by the amount of water vapor the air could hold.  A relative humidity of 75% means air contains 75% of the amount of water vapor possibly held.

Dew point refers to lowest air temperature where water vapor remains in vapor form.  Once the ambient air temperature reaches the dew point temperature the water vapor condenses into dew or liquid.

Dew and fog reference and collection resources available on the web include;

• Fogquest.org is a great informational resource on capturing dew and fog
• A Great & Fascinating design paper about dew catchers 
• Youtube video on dew catcher construction

Air humidity can be a significant component in the irrigation of any green roof system.  Consider those months with lower than average precipitation and check to see if dew occurs frequently.  Validate the average relatively humidity percentages.   Think of the times you have walked across a lawn in the morning to find your shoes soaking wet.

Understanding the value of water vapor in the forms of dew and fog can greatly increase your green roof's survival chances during a drought.  Potable irrigation is not the answer a smart green roof designer looks to for water.

Green Roof with sprinklers on top to keep plants from wilting during drought - giving our industry a bad name..