RAINFALL MEASUREMENT IN CANADA - CHANGING OBSERVATIONAL METHODS AND ARCHIVE ADJUSTMENT PROCEDURES

Precipitation is one of the key components in hydrologic modeling and process studies; however, it is widely recognized that significant err ors in the measurement of precipitation exist. During its 150-yr histo ry, the Canadian Meteorological Service has employed a number of diffe rent precipitation gauges to measure rainfall. This paper will focus o n documenting the types of gauges used in rainfall measurement over th is period. Systematic errors in gauge catch such as wetting loss, wind -induced error, and trace precipitation, which are a result of method of observation and/or gauge design, have been quantified through field and laboratory experiments. A proposed method of adjusting six hourly archived rainfall data (i.e., 1947-present) to provide a compatible a nd consistent rainfall record is described. The combined magnitude of the adjustments for the systematic errors quantified for certain stand ard raingauges can exceed 7%. Results indicate that scientists assessi ng climate change by using monthly correction factors to adjust precip itation may not be accounting for all significant biases in Canadian r ainfall data.