Daly
17.1 Evaporation from surface water

Supporting information

The volume recognised in the water accounting statements (33,137 ML) represents the total volume of water that evaporated from surface water in the Daly region during the 2011–12 year.

The volume is comprised of two components:

Evaporation from Copperfield Dam (137 ML)
Evaporation from rivers (33,000 ML).

Quantification approach

Evaporation from Copperfield Dam

Data source

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

Provided by

Bureau of Meteorology (the Bureau)

Method

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 Copperfield Dam. 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 0.050 (approximately 5 km) national grid.

As a potential evaporation dataset, it is an estimate of the evaporative demand of the atmosphere. The daily gridded climate datasets are generated by the Bureau and include downward solar irradiance, and maximum and minimum air temperatures. The methods used to generate these gridded datasets are outlined in Jones et al. (2007).

The evaporation at Copperfield Dam was estimated from the proportionally weighted average of grid cells that intersected the water feature. The volume was then estimated using the surface area of the storage. In this case, as daily storage level data were unavailable, a static surface area value from the Australian Hydrological Geospatial Fabric was used.

Assumptions, limitations, caveats and approximations

The AWRA-L 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 static surface area for Copperfield Dam from the Australian Hydrological Geospatial Fabric represents the storage at total capacity and, therefore, likely results in an overestimation of evaporation from the storage.

Uncertainty information

Derived from modelled data. The uncertainty estimate was not quantified.

Evaporation from rivers

Data source

Daily pan evaporation data.

Provided by

Department of Land Resource Management.

Method

Evaporation from the rivers within the region is estimated using the MIKE 11 river hydraulic model and is based on measured daily pan evaporation data.

Detailed information on the model calibrations are provided in Knapton et al. (2010).

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty is unquantified.