Adelaide
9.1 Precipitation on surface water

The volume reported (9,770 ML) represents the total precipitation falling onto surface water storages and weirs within the Adelaide region during the 2011–12 year. Precipitation to each surface water storage and weir during the 2011–12 year is provided in the table below.

 ^1–11 Precipitation calculated using dynamic surface area

^12–15 Precipitation calculated using static surface area

National Climate Centre (NCC) daily climate grids (rainfall), Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class, Australian Water Resources Information System (AWRIS)—Water storages.

Monthly precipitation data were produced by the Bureau. These were 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).

Precipitation at each waterbody was estimated from the proportionally weighted average of grid-point cells that intersected each storage or weir (water feature). The precipitation volume was then estimated using the surface area of each waterbody. Surface area varied dynamically with changing storage level for storages, where the relationship between storage level and surface area has been derived. In the Adelaide region, the surface area of the storages was calculated dynamically and the surface area of the weirs is a static value produced from the AHGF.

• 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 lakes.
• Precipitation was only estimated for the surface water storages and weirs (for which data were available) within the Adelaide region and does not include river channels.

The uncertainty estimate is not quantified.

In the 2011 Account, storages used for urban water supply only (located off-stream and which harvested only minimal catchment runoff) were reported at line item 3.1 'Urban water system'. These storages were Barossa Reservoir, Happy Valley Reservoir, Hope Valley Reservoir and Onkaparinga Summit Reservoir.

In the 2012 Account, these storages were reported at line item 1.1 Storages in order to be consistent with the classification of storages applied to the other regions of the 2012 National Water Account. As a consequence, the 2010–11 volume of line item 9.1 'Precipitation on surface water' was restated in order to include precipitation on the storages that were previously considered part of the urban water system as per the following table.