Water quantity in Canadian Rivers indicators: data sources and methods, chapter 2

2. Description and rationale of the Water Quantity in Canadian Rivers indicators

2.1 Description

The Water Quantity in Canadian Rivers indicators classify water flow data from water quantity monitoring stations across Canada as high, normal or low. The national indicator summarizes ratings for 2001-2013, while the regional and local indicators report results for 2013 only. Water quantity classifications are determined by comparing water flows for each day of the reported year to the associated daily normal values for 1981-2010 from each monitoring station.

2.2 Rationale

Canada has 0.5% of the world's population and its landmass contains approximately 7% of the world's renewable freshwater supply. The Water Quantity in Canadian Rivers indicators provide information about the state of, and changes in, current surface water quantity to inform management of water resources.

2.3 Recent changes to the indicators

The methodology for these indicators have been reviewed and updated since it was last published in 2014. Changes to the indicator include the following:

  • While both water levels and flows were previously used in the calculation of the water quantity indicators, the methodology now uses data from flow stations only. Stream flow refers to the volume of water that moves over a designated point (e.g., stream gauge) over a fixed period of time. It is expressed in cubic metres per second (m3/s). This change was made to produce indicators that are more comparable between locations.
  • The regional water quantity indicator is now calculated by accounting for the upstream area represented by a water quantity monitoring station within a drainage region. Water quantity in a drainage region is classified based on the amount of water leaving the drainage region, rather than using a statistical descriptor as is done in the national and local indicators. The previous calculation method for the regional water quantity indicator involved grouping water quantity stations by drainage region and counting the number of stations within each category (low, normal, high) for each drainage region. The mode, or most common classification, was used to categorize the water quantity in each drainage region.
  • The national indicator has been redesigned to track trends in water quantity across Canada. The indicator now summarizes the percentage of local stations classified as low, normal or high from 2001 to 2013. In previous publications, a count of the number of drainage regions classified as low, normal or high was used.
  • Additionally, data for some stations in the Northern Quebec drainage region are unavailable between 1999 and 2008. This data gap affects the completeness of the 1981-2010 normal period and daily percentile values cannot be calculated due to a lack of data. The normal period was changed to 1971-2000, instead of 1981-2010, for the calculation of the local and regional water quantity indicators in the Northern Quebec drainage region only.
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