41.1 Precipitation on storages
The volumetric value for the line item for the 2010–11 year was 483,118 ML. The line item represents precipitation volumes on major surface water storages within the Murray–Darling Basin (MDB) region. The line item value applies only to the Southern Basin. Line item includes precipitation on Menindee Lake (100,897 ML), Hume Reservoir (238,262 ML), Dartmouth Reservoir (72,524 ML) and Lake Victoria (71,435 ML) within the MDB region.
Precipitation information for other storages is available (see line item 9.1). However, information is provided only for above four storages to be consistent with information provided in other storage line items (line items 41.3, 42.1, 42.4, 42.5 and 42.6).
Monthly precipitation data was produced by the Bureau. It was based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (approximately 5 km) national grid (Jones et al. 2007).
The precipitation 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 surface area varied dynamically with changing storage level for storages, lakes and weirs where the relationship between storage level and surface area had been derived.In the MDB region, Precipitation on the surface water store included the precipitation falling on the water bodies mentioned in the supporting information.
Assumptions, Limitations, Caveats and Approximations
The precipitation estimates were subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
The dynamic storage surface areas calculated from the levels and capacity 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 surface area is an approximation only. It represents the lakes at capacity and therefore likely results in an overestimation of precipitation on the lake.
Volumes were derived from estimated data. The uncertainty estimate was not quantified.