Water Budget for Australia
The Cycles

The water cycle describes the continuous movement of water between the earth’s major reservoirs including the ocean, ice, atmosphere, water bodies on land, vegetation and soils. Although the balance of water on Earth remains fairly constant over time, water moves between the various reservoirs in response to climate variability and change. Some of the processes involved in driving the transfer of water from one reservoir to another and between physical states (liquid, solid, gas) include evaporation, transpiration, condensation, precipitation, infiltration, runoff, and subsurface flow.

The water budget figure shows all major water flows for Australia averaged for the period 1990-2011 (Haverd et al. 2013b; The Tools - HYPERLINK). It includes precipitation, soil evaporation, transpiration (loss of water primarily through the stomata of vegetation), wet canopy evaporation (loss of water on vegetation arriving as precipitation and condensation), changes in stored water in soils (including from soil moisture and the water table), and runoff (water being transported laterally into land water bodies and ultimately into the ocean).


Mean annual precipitation for the period was 504 mm, just 62% of the global average. Of this amount, almost half (48%) was evaporated straight from the soils without contributing to net primary production of vegetation, a quantity well above the global average. An additional 14% went into runoff. Plant transpiration accounted for 34% of the total precipitation and only about 1% represented a positive change in stored soil water.


Continentally, low precipitation and high soil evaporation lead to NPP being lower than the global average (69% of the global value) and there is a high proportion (56%) of NPP attributable to grassy vegetation (including crops and the grassy component of savannas).

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