9.1 Precipitation on surface water
This line item relates to precipitation on the major storage and lakes within the Canberra region.
The total volume of rainfall on storages is 21,110 ML during the 2011–12 year within the Canberra region as given in the following table.
|Water storage type||Water storage name||Precipitation (ML)|
|Lakes||Lake Burley Griffin5||5,525|
1–4 Precipitation calculated using dynamic surface area
2–7 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 storage.
Monthly precipitation data were produced by the Bureau. 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. The average monthly surface area of the major storages was calculated from daily storage levels and capacity tables. 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 total surface area of the surface water store within the Canberra region included only the reservoirs and urban lakes. River channels were not included.
The uncertainty estimate was not quantified.
The Bureau recalculated the 2010–11 year volume published in the 2011 Account using the improved dataset with newly available data. Consequently, the volume has been updated from 19,787 ML (as published in the 2011 Account) to 19,713 ML.