Precipitation change indicator: data sources and methods, chapter 2

2. Description and rationale of the Precipitation Change in Canada indicator

2.1 Description

The Precipitation Change in Canada indicator measures the annual and seasonal precipitation departures (or anomalies) for the years 1948 to 2014. For this indicator, the annual departure is the percentage difference of the value of a given year against a reference value as denominator. The reference values used in this indicator are the annual and seasonal precipitation averages for the period of 1961 to 1990 (often referred to as the 1961-1990 normal). This reference period is consistent with the approach used to compare anomalies in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report and the World Meteorological Organization (WMO) Annual Statements on the Status of the Global Climate. The indicator is calculated using data from weather stations across Canada with sufficiently long data records to allow for a meaningful trend calculation. Total precipitation includes the combination of rainfall and snowfall.

2.2 Rationale

Much of Canadian economic and social activity is climate dependent. Understanding how Canada's climate is changing is important for developing adaptive responses. The Precipitation Change in Canada indicator helps show how Canada's precipitation has changed since nationwide recording of consistent and comparable climate observations began in 1948.

The IPCC and the United Nations Framework Convention on Climate Change (UNFCCC) use precipitation, among other variables, to assess long-term changes in climate. Precipitation is considered by the WMO Global Climate Observing System (GCOS) as an Essential Climate Variable.