17.1 Evaporation from surface water

Supporting information

The volume reported in the water accounting statements (32,761 ML) represents the total volume of evaporation from the major surface water storages within the Perth region during the 2011–12 year.

Total volume of evaporation from each storage during the 2011–12 year within the Perth region is provided in the following table.


Evaporation from each storage within the Perth region during the 2011–12 year


Evaporation (ML)



Churchman Brook


Drakes Brook




Logue Brook




North Dandalup


Samson Brook




Serpentine Pipehead


South Dandalup













Quantification approach

Data source

Daily climate grids (temperature and solar radiation), Australian Hydrological Geospatial Fabric—waterbody feature class, Australian Water Resources Information System—water storages.

Provided by

Bureau of Meteorology.


The potential evaporation estimate produced by the Australian Water Resources Assessment system Landscape model (AWRA-L) version 2.0.0 (Van Dijk 2010) was used to calculate evaporation from the surface water store. The AWRA-L model uses a modified version of the Penman-Monteith method to produce the potential evaporation. Daily AWRA-L potential evaporation grids were produced based on daily gridded climate data that were available on a 0.05 degree (approximately 5 km) national grid.

As a potential evaporation dataset, it was an estimate of the evaporative demand of the environment. The daily gridded climate datasets are generated by the Bureau 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-cells that intersected each water feature. The volume was then estimated using the surface area of each waterbody. The average monthly surface area of the major storages was calculated from daily storage levels and capacity tables.

The surface area of all of the storages in the Perth region was calculated using this dynamic method.

Assumptions, limitations, caveats and approximations

The AWRA-L potential evaporation estimates are subject to approximations associated with interpolating the observation point data to a national grid as detailed 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 temporal scale.

The total surface area of the surface water store within the Perth region included only the storages (and not the rivers).

Uncertainty information

The uncertainty estimate was not quantified.