Rainfall Measurement in Canada: Changing Observational Methodsand Archive Adjustment Procedures

Abstract

Precipitation is one of the key components in hydrologic modeling and process studies; however, it is widely recognized that significant errors in the measurement of precipitation exist. During its 150-yr history, the Canadian Meteorological Service has employed a number of different precipitation gauges to measure rainfall. This paper will focus on documenting the types of gauges used in rainfall measurement over this 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 and consistent rainfall record is described. The combined magnitude of the adjustments for the systematic errors quantified for certain standard raingauges can exceed 7%. Results indicate that scientists assessing climate change by using monthly correction factors to adjust precipitation may not be accounting for all significant biases in Canadian rainfall data.