9.1 Precipitation on surface water
This line item relates to precipitation on the major storage and lakes within the Canberra region.
|Water storage type||Water storage name||Precipitation (ML)|
|Lakes||Lake Burley Griffin2||5,477|
1 Precipitation calculated using dynamic surface area
2 Precipitation calculated using static surface area
Monthly precipitation data were produced by the Bureau of Meteorology. They 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).
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 where the relationship between storage level and surface area had been derived. In the Canberra region, the surface area of the four storages was calculated dynamically and the surface area of the three urban lakes was a static value produced from the AHGF.
In the Canberra region, precipitation on the connected surface water store included the precipitation falling on major storages and urban lakes only.
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 lakes.
The uncertainty estimate was not quantified.
This line item corresponds to line item 13.1 Precipitation on connected surface water reported in the 2010 Account. The data available for precipitation calculation have improved since the 2010 Account publication.
|2010 Account line items||Volume for the 2009–10 year reported in the 2010 Account (ML)||Difference due to prior period error correction and scope change (ML)||Volume for the 2009–10 year reported in the 2011 Account (ML)|
|13.1 Precipitation on connected surface water||11,035||371||11,406|
The volume of precipitation on surface water estimated for the comparison year (11,035 ML) using the improved dataset is less than the volume reported for the 2010 Account (11,406 ML). This is because the gridded precipitation surfaces that these estimates are produced from are derived from a large number of precipitation monitoring sites. Many of these precipitation sites are manually monitored with observed precipitation recorded on paper and mailed to the Bureau of Meteorology. There can be a considerable delay between the date of precipitation and the data becoming part of the interpolated precipitation surfaces; thus historical surfaces can change as more data become available.
The difference of 371 ML represents a change of approximately 3% of the originally published volume. The 2011 Account comparison year uses the volume of 11,406 ML reported in the 2010 Account.