30.1 Precipitation on off-channel water store
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 Canberra region was divided up into five subregions for the purpose of estimating the water balance of the private store. The four of the subregions were the catchments of the major storages and the fifth was the remaining land.
The private store consisted of off–channel storages filled primarily by rainfall-runoff. These were determined from waterbody mapping provided by Geoscience Australia and were waterbodies that were greater than 50 m from built-up areas in the Canberra region.
The average precipitation depth across the Canberra subregions was determined as the weighted mean of precipitation occurring from the relevant grid points within the region boundary. Points were weighted upon the area they represented within the Canberra landscape to remove edge effects (where the area represented is not wholly within the reporting region) and the effect of changing area represented with changing latitude. The average precipitation depth was used as an input into the STEDI model (Sinclair Knight Merz 2011) converted the depth of precipitation to a volume using the surface area of private storages within a region.
Assumptions, Limitations, Caveats and Approximations
- The gridded climate input data are subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
- The spatial extent of waterbodies subject to the assumptions and methods associated with the data provided by Geoscience Australia.
The uncertainty estimate was not quantified.