Evapotranspiration is the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere.


Rainfall Interception: This is the estimate of proportion of subcatchment where rainfall is intercepted by vegetation. This value will then directly effect the total evapotranspiration.

Medium to heavy grass or light to medium forest 0.7 -0.9

However, Chapman (1970) adopted the range 0.3 – 0.5 for mulga scrub. The choice of value will have little effect on runoff volumes.

Maximum Potential Evapotranspiration from Upper Soil: Maximum rate at which plant roots in the upper soil can remove water in mm/day. The actual maximum rate is reduced from this rate in proportion to actual moisture content.

Maximum Potential Evapotranspiration from Lower Soil: Maximum rate at which plant roots in the lower soil can remove water in mm/day. The actual maximum rate is reduced from this rate in proportion to actual moisture content.

 

Source: Bureau of Meteorology, Product ID code : IDCJCM0008

 

Source: Bureau of Meteorology, Product ID code : IDCJCM0008

Proportion of Evapotranspiration from Upper Soil: Estimated proportion of ET from upper soil zone, which may also be related to vegetation. It is considered to be the proportion of the catchment not covered by deep rooted vegetation. However, even catchments vegetated entirely with grass are likely to have some drain on the lower soil zone store and values are usually in the range of 0.5 – 0.85.

Potential Evaporation Ratio: Ratio of potential evaporation to standard pan evaporation.

 

Source: Bureau of Meteorology, Product ID code: IDCJCM0006

 

Source: Bureau of Meteorology, Product ID code: IDCJCM0006

The parameters discussed above are important for calibration, The most important are Dry Sorptivity, Depression Storage Capacity, Upper Soil and Lower Soil Storage Capacities. The least important are Moisture Redistribution Parameters. Lower Soil Drainage Factor and Constant Rate Groundwater Recession Factor are important in the determination of groundwater runoff, but since this is usually a comparatively small part of the total runoff volume the overall importance of these two parameters is not generally very great.