Perth
9.1 Precipitation on surface water

This line item refers to total precipitation on the major surface water storages within the Perth region.

The total volume of rainfall on each storage during the 2010–11 year within the Perth region is provided in the following table.

 

Total rainfall on each storage within the Perth region during the 2010–11 year

Storage	Rainfall (ML)
Canning	1,190
Churchman Brook	101
Drakes Brook	151
Harvey	1,696
Logue Brook	608
Mundaring	1,777
North Dandalup	1,296
Samson Brook	106
Serpentine	2,424
Serpentine Pipehead	375
South Dandalup	2,492
Stirling	1,447
Victoria	229
Waroona	278
Wungong	1,467
Total	15,637

 

Bureau of Meteorology: monthly precipitation grids, Australian Hydrological Geospatial Fabric waterbody feature class and water storages.

Bureau of Meteorology.

Monthly precipitation data were produced by the Bureau. Precipitation was based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (5 km) national grid (Jones et al. 2007). 

The precipitation on each waterbody was estimated from the average of the grid points within a 5 km radius of each water feature. The volume was then estimated using the surface area of each waterbody. The average monthly surface area of the major storages was calculated from daily storage levels and capacity tables.

The surface area of all the storages in the Perth region was calculated using this dynamic method.

The precipitation estimates were subject to approximations associated with interpolating the observation point data to a national grid as 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 total surface area of the surface water store within the Perth region included only the storages (and not the rivers).

The uncertainty estimate was not quantified.

The following table presents substantive changes in the line item reported in this 2011 Account with the corresponding line item in the 2010 Account.

Comparative year information for line item 9.1

2011 Account line item	2010 Account line item	2011 Account volume for the 2009–10 year (ML)	2010 Account volume for the 2009–10 year (ML)	Change from the 2010 Account to the 2011 Account
9.1 Precipitation on surface water	13.1 Precipitation on connected surface water	26,590	28,360	Data availability: rainfall data not available last year were added to the gridded precipitation dataset Change in line item name and number

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 and there can be a considerable delay between the date of precipitation and the data being stored in the Bureau database. Thus, historical precipitation surfaces can change as more data become available.

Using this improved dataset to recalculate rainfall on storages for the 2009–10 year resulted in a 7% decrease in volume compared with that reported in the 2010 Account. It is considered that, although this change is relatively minor (less than 10%), this is an important line item for reliable estimates of inflows into water storages for the region.