Daly
9.1 Precipitation on surface water

Supporting information

The volume recognised in the water accounting statements (32,132 ML) represents the total volume of rainfall that fell on surface water in the Daly region during the 2011–12 year.

The volume is comprised of two components:

  • Rainfall on Copperfield Dam (132 ML)
  • Rainfall on rivers (32,000 ML).

Quantification approach

Rainfall on Copperfield Dam

Data source

Monthly precipitation grids, Australian Hydrological Geospatial Fabric—waterbody feature class and stream network feature class, Australian Water Resources Information System—water storages.

Provided by

Bureau of Meteorology.

Method

Monthly precipitation grids were produced using daily data from approximately 6,500 rain gauge stations and interpolated to a 0.050 (5 km) national grid (Jones et al. 2007).

The precipitation at Copperfield Dam was estimated from the proportionally weighted average of grid cells that intersected the water feature. The volume was then estimated by multiplying by the surface area of the storage. In this case, a static surface area value from the Australian Hydrological Geospatial Fabric was used.

Assumptions, limitations, caveats and approximations

The precipitation estimates were subject to approximations associated with interpolating the observation point data to a national grid as detailed in Jones et al. (2007)

The use of the static Australian Hydrological Geospatial Fabric waterbody feature class surface area is an approximation only. It represents the storage at total capacity and therefore is likely to result in an overestimation of precipitation on the storage.

Uncertainty information

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

Rainfall on rivers

Data source

Monthly precipitation grids.

Provided by

Bureau of Meteorology.

Method

The volume of precipitation that fell on rivers during the 2011–12 year is an estimate only. 

The estimate was based on the ratio of precipitation (132 ML) to evaporation (137 ML) that occurred on Copperfield Dam. The ratio (0.96) was then applied to the volume of evaporation from rivers (33,000 ML) (see line item 17.1) to derive the approximate rainfall on rivers.

Assumptions, limitations, caveats and approximations

It is assumed that the ratio of precipitation to rainfall for storages is the same for rivers.

Uncertainty information

The uncertainty is unquantified.