Alberta River Flow Quantity Index: More about the data

The indicator is based on the assumption that a natural, average flow regime can be expected to occur about 90% of the time and is indicated by a green color on the index. The other 10% of the time, the river regime will be naturally at an “above average” (blue) or “below average” (yellow or orange) state, but these are still considered natural fluctuations and are to be expected from time to time. Natural ecosystems require variability in flow to support their long-term health. If above average or below average conditions are observed more regularly, then impacts of human activity are beginning to show in the indicator but the river is still technically within its historical flow range. Changes to the existing ecosystems may be observed over the longer-term if these conditions persist.

Once the “outside of natural” criteria have been triggered, either at the increased (purple) or reduced (red) state, the seasonal flow regime of the river has been changed by humans and is definitely outside of its normal, natural range. At this point we would expect to see ecological impacts to the existing aquatic ecosystem, becoming more permanent if the conditions are persisting and are not just single-year or infrequent occurrences. These changes can result both from exceptionally low flows but also from unnaturally sustained high flows.