Water availability indicator: data sources and methods, chapter 4


4. Methods

Environment Canada estimated water demand for 2009 for each sub-drainage area (SDA) as the sum of municipal, industrial and agricultural water withdrawals from all flowing water.

Water supply for 2009 is calculated using streamflow data collected by the Water Survey of Canada's hydrometric stations. The water flow (cubic metres per second [m3/s]) data is extracted for the hydrometric station located at the basin outlet. Flow values from the outlet station are considered to be approximately equal to the water supply for the entire basin. Any water consumed in the basin was added to the water supply to estimate all water theoretically available for use. Adding water consumed gives the total water supply for the basin. For cases when the most-downstream station’s flow did not account for the flow in the entire basin, proportions were used to estimate water supply for the basin.

Environment Canada calculated water availability for 2009 by dividing water demand by water supply for each sub-drainage area (SDA). All SDAs are assigned one of the Organisation for Economic Co-operation and Development's (OECD) four water availability threat classificationsFootnote [1] based on the water availability ratio.Footnote [2] While not always applicable to Canadian circumstances, the OECD defines these classifications as follows:

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