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Surface Water Quantity — Precipitation




Precipitation is the total amount of water that falls on the ground in the form of rain, snow and hail. Total precipitation is expressed in millimetres (mm). Part of the precipitation flows on the ground towards rivers, part of it seeps down into the ground, and part of it goes back to the atmosphere through evaporation and transpiration by plants.

Precipitation data is used by the RVCA in flood forecasting, flood risk assessment and drought analysis and by others for such things as reservoir management, agricultural activities, road system and storm water management and recreation planning.

Click here to learn more about the water cycle.




The standard precipitation measuring method is a canister set into the ground in a level area with no obstructions nearby. The precipitation that falls into the canister over a set time period (for example, every three hours or once a day) is the total precipitation for that time. Electronic gauges are also used that weigh the amount of precipitation or count the number of tips of a small bucket that holds the equivalent of 2 mm of water. The data from both types of gages can be converted to electrical signals and transmitted to distant receivers or be recorded in data-loggers in digital format for later retrieval.

In and around the Rideau Watershed, there are six stations where precipitation data is being collected on a long term basis by AES.

  • Ottawa Airport (since 1938)
  • Russel (since 1954)
  • Brockville (since 1965)
  • Drummond Centre (since 1984)
  • Godfrey (since 1981)
  • Kemptville (since 1928)

Hourly and daily precipitation and other climate data is now available online from Environment Canada for the Ottawa Airport and other major recording stations in Canada at http://www.weatheroffice.ec.gc.ca

The RVCA is in the process of developing a precipitation monitoring system. There will be automatic rain gauges, as well as a volunteer observer network. As data becomes available, these will be posted in this site.