Canberra

Data source

Bureau of Meteorology: National Climate Centre (NCC) version 3 daily rainfall grids; NCC daily maximum temperature grids; NCC daily minimum temperature grids; NCC daily satellite observed solar radiation grids; Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; Water Storages, Australian Water Resources Information System (AWRIS).

Data provider

Bureau of Meteorology (the Bureau).

Method

Evaporation from the connected surface water store was estimated using monthly open water evaporation data produced by the Bureau. 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 Tmax) – (saturation vapour pressure at Tmin).

This potential evaporation data-set is an estimate of the evaporative demand of the atmosphere. The daily gridded climate data-sets are generated by the Bureau and include precipitation, downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded data-sets 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 of the storages in the Canberra region was calculated using this dynamic method. Storage rating table and regular level data were not available for the lakes in Canberra, so the default AHGF waterbody feature class was used to estimate a static surface area. In Canberra, the evaporation from the connected surface water store included the storages and lakes.

Uncertainty

Ungraded.

Assumptions, approximations and caveats/limitations

• The Penman 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 use of the static default AHGF waterbody feature class surface area was an approximation only. It represented the lakes at capacity, and therefore likely resulted in an overestimation of evaporation from the lakes.