Did you know? Cloud stripping in the Wet Tropics

How often we climb to the top of a mountain anticipating a spectacular view, only to find ourselves looking at the inside of a cloud instead? Indeed, how often do we look up and find peaks like Mount Bartle Frere, Mount Bellenden Ker or Thornton Peak obscured by mist?

Anyone who has stood inside one of those clouds knows that it is a moist place; water condenses on hair, clothes and vegetation. Recently, CRC Rainforest researchers decided to measure the amount of water which is obtained by upland forests through ‘cloud-stripping’, as the process is known, compared with that obtained directly from rainfall.

By putting collars around the stems and trunks of trees, and placing troughs below the canopy, they were able to measure the total amount of water reaching the ground. By comparing that total with the amount collected in a rain gauge, they were able to calculate how much extra water had been stripped from the clouds. They also measured it directly with an instrument composed of a mesh attached to a rain gauge which they set up under a roof to keep out the rain. Cloud moisture condensed on the mesh and dripped into the rain gauge.

Astonishingly, it was discovered that as much as 40 percent more water was harvested from the clouds than was measured, as rain, in the standard rain gauge (see graph). This has important implications for not only the upland forests but also for forests at lower altitudes – and for the people who inhabit the area. The upland forests use very little of the water they harvest. The leaves are almost constantly wet and clouds block off sunlight which would otherwise drive the transpiration process. However, these forests act as a reservoir, storing huge volumes of water which are released gradually, keeping our creeks and rivers flowing through the dry season.

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