South East Queensland
42.1 Evaporation from storages
This line item represents the evaporation from Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe.
The following quantification approach shows the method used to calculate the evaporation from all storages. Only the component for Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe is relevant to this line item.
The Priestly and Taylor method to estimate potential evaporation (as calculated by the WaterDyn model [Raupach 2008]) was used to estimate evaporation from the surface water store. Monthly potential, open water evaporation data produced by the Bureau of Meteorology were used, based on daily gridded climate data that are available on a 0.05 degree (5 km) national grid.
Potential evaporation is an estimate of the evaporative demand of the environment. The daily gridded climate datasets used to produce this estimate are generated by the Bureau of Meteorology and include downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded datasets are outlined in Jones et al. (2007).
The evaporation at each waterbody was estimated from the proportionally weighted average of grid points that intersected each water feature. The volume was then estimated using the monthly average surface area of each waterbody. The surface area varied dynamically with changing water storage level for water storages where the relationship between storage level and surface area had been derived.
Assumptions, Limitations, Caveats and Approximations
The Priestly and Taylor potential evaporation estimates are subject to approximations associated with interpolating the observation point input data to a national grid as described in Jones et al. (2007).
The dynamic storage surface areas calculated from the levels and storage rating tables represent a monthly average and therefore will not capture changes that occur on a shorter timescale.
The uncertainty estimate was not quantified.