Water quantity in Canadian Rivers indicators: data sources and methods, chapter 5
5. Caveats and limitations
Extreme short-term events may not be detected with the indicators, since the focus is on frequency of observations in different categories through the year. Large events of short duration, such as a flood, may not influence the final classification of a station.
The number of water quantity monitoring stations included in these indicators fluctuates from year to year because stations may be closed as monitoring networks are optimized. Whether or not the data have been verified and uploaded into HYDAT by the time the data are extracted to calculate the indicator also influences whether the station is included in the calculation that year.
While 30-years represents a long time series for water quantity data, it represents a relatively short historical time frame for a given river and does not account for all natural variability in a river system. The status of water quantity assessed by the present indicators are a reflection of its time period and do not necessarily reflect longer-term trends at the station.
The water quantity for the Great Lakes drainage region is based on rivers draining into the Great Lakes and not on the water contained within the Great Lakes themselves.
Most water quantity monitoring stations in Canada are located in populated areas and do not represent the country's entire geographic extent or all its watersheds. There are insufficient stations in areas such as the North to compute complete, nationally representative indicators.
Water flow data collected at a hydrometric station are representative of the average conditions of the upstream drainage area. The variability of conditions across this area may not be reflected, and water quantity classifications of tributaries may differ from that described by the indicators. Professional judgment is used to determine whether there were sufficient stations to describe a drainage region. For example, the six stations in the Arctic Coast Islands drainage region were considered insufficient to categorize water quantity for the region in 2013.
Water quantity generally follows a predictable seasonal pattern with natural, year-to-year variability. The indicators compare daily values to the 30-year normal and assumes that water quantity is approximately the same from one year to the next for the same calendar day. A shift in the predictable seasonal pattern (the hydrograph) one year will influence the results.
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