Water that ends up in Sylvan Lake starts out as rain and snow precipitation that falls within the watershed boundary. There are no other sources of water input. Precipitation that falls directly onto the lake surface plus runoff and urban stormwater from the land, and groundwater that enters the lake underground all affect the lake level. Check the Water Quantity category on this website for other postings on this topic.
Historically the lake level in mid-Summer has been about 936.75 metres above sea level according to Alberta Environment records. The current lake level is 937.2 metres, significantly above the long term average high water mark of about 937.0 metres.
Has the extra water come from higher-than-usual precipitation? Here are the facts:
Seventy years of Total Precipitation data collected at the Red Deer Airport between 1940 and 2011 are plotted in this graph. That weather station is a reliable Environment Canada WeatherOffice site and its data should represent Sylvan Lake’s weather in the absence of a station located within the watershed. The average annual Total Precipitation in the region has been 0.466 metres. The amount has varied between a high of 0.63 meter and a low of 0.29 metre during the 70 year period.
Total Precipitation can vary dramatically from year to year. This graph shows the year-to-year change since 1940. Differences since 2000 are within the historic range.
Statistically speaking, during the last 70 years annual total precipitation values have been within +/- 10 percent of the average about 80 percent of the time. In 15 percent of the years the values have been up to 37 percent greater than the average. In 11 percent of the years the values have been up to 40 percent below the average. See the analysis of all the data in this graph.
As the Total Precipitation record for the region has not changed much over 70 years but the Sylvan Lake level is above the long term average high water mark shown here, then other factors like the evaporation rate must be controlling the quantity of water in Sylvan Lake.