Aug 06

Evapotranspiration. The Movement of Water. Environmental Issues.

Evapotranspiration and Global Dimming.


Evapotranspiration (ET) is a generalised term for the transfer or movement of water, as water vapour, into the atmosphere from both vegetated and non-vegetated land surfaces. It is affected by climate, availability of water and type of vegetation. ET is a large component of the water balance across Australia, because almost 90 per cent of precipitation (rainfall or in some cases hail or snow) is returned through ET to the atmosphere. Despite its importance, ET has until recently been very difficult (if not impossible) to measure directly and hence there is little available information available to quantify ET currently. Recent development of new technology using satellite imagery now allows evapotranspiration to be comprehensively measured in a cost-effective manner.

Australian Water Resources



A Large Gum Tree can evapotranspire 1000 litres in a day!



It is believed that a large Eucalyptus tree can evaporate up to 1000 litres of water a day during the peak evaporation period in summer. This kind of data was collected during experiments where a plastic bag was sealed off around a branch of leaves on a living tree and the water was collected and measured after one day.


Evapotranspiration is also said to be the method by which a tree transports the water soluble nutrients around the Trees System and plays an integral part in photosynthesis.




Recent experiments and surveys involving pan evaporation tests ( A method carried out over the past century where a pan is placed into the environment and the reduction in water via evaporation is measured daily) have shown that global dimming has decreased the amount of evaporation into the atmosphere in a significant way!


Global Dimming Documentary


What does this Mean to Our Trees?


This phenomena will cause problems for vegetation or bio mass globally. If the physical amount of water available in the atmosphere is reduced, coupled with lowered levels of sunlight, then the photosynthesis capability of plants will be reduced.

Some researchers have already undertaken studies where growth patterns of large trees have been noted to be significantly reduced in comparison to previous centuries.


What Can I Do?


Always use a good natural mulch around the garden. This can be purchased from you local tree lopper for a reasonable price, and they will usually deliver it to your location.

Spread the mulch to a depth of 10 centimeters and avoid the mulch coming into contact with the trunk or stems of plants or trees.

Avoid making large lawn areas in new gardens as these are giant evaporation pans and are environmental disasters.


Mulch Gardens look great and are good for the environment!


Instead plant trees and shrubs around the home that are endemic to the area and where possible make a mulch garden! During summer water the garden later in the day.



Always employ the services of a qualified Tree Removal Expert when pruning or thinking about getting any work done to a tree in your garden. The results of using an inexperienced and un knowledgeable Tree Lopper, can have far greater ramifications than you think.


Contact your local Arborist for more information regarding evapotranspiration.

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