Perth

This line item refers to total evaporation from all the major reservoirs within the Perth region.

Total volume of evaporation from each reservoir during 2009-10 within the Perth region is provided in the table below.

Data source

Bureau of Meteorology: National Climate Centre daily climate grids (rainfall, temperature and solar radiation), Australian Hydrological Geospatial Fabric waterbody feature class and Australian Water Resources Information System water storages.

Data provider

Bureau of Meteorology.

Method

Evaporation from the connected surface water store was estimated using monthly open water evaporation data produced by the Bureau of Meteorology. It is a Penman evaporation estimate based on daily gridded climate data and is available on a 0.05 degree (5 km) national grid. The Penman method estimates the evaporation that would occur from a small open waterbody and assumes the evaporation does not modify the meteorology through evaporative cooling. It assumes aerodynamic conductance of 0.01 m/s and saturation deficit is estimated as (saturation vapour pressure at T_max) – (saturation vapour pressure at T_min).

As a potential evaporation dataset it was an estimate of the evaporative demand of the atmosphere. The daily gridded climate datasets are generated by the Bureau of Meteorology and include precipitation, 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 average of the grid points within a 5 km radius of 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 storages in the Perth region was calculated using this dynamic method.

Uncertainty

Ungraded.

Approximations, assumptions, caveats/limitations

• The Penman evaporation estimates are subject to approximations associated with interpolating the observation point data to a national grid 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 time-scale.
• The total surface area of the surface water store within the Perth region included only the reservoirs (and not the river channels).