By Chris Moss, resident of Otter Point

In our temperate climate it is not unusual to see clouds in the trees.  Many times these clouds do not appear to be part of any other weather system. They seem to appear spontaneously in the forested areas of our region.  They are the result of the transpiration of trees pushing water vapour into the air which then condenses into clouds.  But there is more going on than just a simple mini “water cycle”.  The complexities of cloud formation in forests globally has only recently been studied using years of data from satellites.  In 2021 the  Journal Nature Communications (1) published an extensive review of cloud formation in forests and their effect on global climate.

“Forests play a key role in humanity’s current challenge to mitigate climate change thanks to their capacity to sequester carbon. Preserving and expanding forest cover is considered essential to enhance this carbon sink. However, changing the forest cover can further affect the climate system through biophysical effects. One such effect that is seldom studied is how afforestation can alter the cloud regime, which can potentially have repercussions on the hydrological cycle, the surface radiation budget and on planetary albedo itself. Here we provide a global scale assessment of this effect derived from satellite remote sensing observations. We show that for 67% of sampled areas across the world, afforestation would increase low level cloud cover, which should have a cooling effect on the planet. We further reveal a dependency of this effect on forest type, notably in Europe where needleleaf forests generate more clouds than broadleaf forests.”

Low level forest clouds reflect the sun’s energy, thereby lowering temperature. The clouds retain moisture and return it to the forested area.  In non-forested areas the moisture is drawn directly upwards and if there is enough moisture this can form higher level clouds. However, high level clouds like cumulus and thunderclouds usually dissipate as soon as the sun’s warmth fades.  They can flatten and form a layer of status cloud that traps heat and reflects it down to the ground and increases night time temperatures. 

“The fact that Earth’s vegetation cover can affect rainfall has been known for a long time. The Amazon forest generates about half of its own rainfall by recycling moisture lost through evaporation.”

During the B.C. heat dome of 2021 the Island town of Tofino nearly ran out of water.  The Mayor explained that it was only through the existence of trees on Muir’s Island ( because they had been saved from logging) that captured wet moist air and fog blowing in from the ocean every day and dropped it to the ground and into the Tofino water catchment system, that the town avoided a total shutdown of its water system.

We must be aware of the changes we make when we reduce or level the forest around us.  If we upset the balance we will find ourselves in a hotter dryer climate, with a loss of bio-diversity, and drought very quickly.

• Duveiller,Filipponi,Ceglar,Bojanowski,Alkama,Cescatti,Alessandro.2021,
  Revealing the widespread potential of forests to increase low level cloud cover
  Nature Communications