In general, we have a good understanding of the past and present state of surface water quantity in Alberta. We also know the location, extents and history of most of Alberta's aquifers. It is important know the average water quantity, but more importantly, we need to understand the short term variability and the long-term changes in water quantity.

There are two major factors that affect the daily, monthly, and yearly differences in streamflow, water levels and groundwater elevations:

1. natural variations in climate occurring in different cycles and time scales;
2. Changes due to human activity and developments.

Streamflow varies within each year, from one year to the next, and over the long-term in response to climatic variability and human impacts. This concept is illustrated here.

The average monthly flows for each of the last nine decades for the North Saskatchewan River at Edmonton are represented by the coloured bars. Overall, some decades were wetter than average while others were drier.

For example, the average flow in July in the early part of the century was about 700 m³/s, however during the past decade it was about 400 m³/s.

In this graph it appears that flows in the river have declined over time but this is one of the pitfalls of looking at recorded data without understanding the underlying changes that have occurred in the basin. In fact, two major dams that regulate the flow of the North Saskatchewan River were built during the period represented by this chart. This resulted in reduced average summer flows and increased winter flows (from about 40 m³/s near the turn of the century to around 120 m³/s now). Municipalities and industry have also diverted increasing amounts of water from the river over time. It is important to take the consumptive uses and effects of regulation into account when conducting trend analyses on annual river volumes. Human effects can often explain an apparent negative trend in recorded streamflow volumes.

To fully understand what has happened in the past and to comment on future outcomes you need to know more than the most recent water quantity data. A number of factors including the changes resulting from human development and climate variability are examined to understand the variability in water quantity. Lake levels, groundwater elevations, and river flows indicate the net effects of all of these factors.