Future Changes in Precipitation Extremes Over Canada: Driving Factors and Inherent Mechanism

In this study, future changes in precipitation extremes over 10 climatic regions in Canada and their mechanism under Representative Concentration Pathways (RCPs) throughout the 21st century are investigated by using the Providing Regional Climates for Impacts Studies (PRECIS) model. The performance of PRECIS in hindcasting total and extreme precipitation for the historical period is first evaluated through two experiments driven by the boundary conditions from both ERA-Interim (1979-2011) and HadGEM2-ES (1959-2005). The validation results indicate that PRECIS can reasonably reproduce both the magnitudes and spatial patterns of precipitation extremes over Canada. Changes in total and extreme precipitation for two future periods are analyzed to explore how regional climate over different climatic regions would respond to global warming. Mechanism governing changes in precipitation extremes is explored through a comprehensive analysis of potential climate factors and their correlations and interactions with precipitation extremes. There are obvious increasing trends over most regions for the magnitude of precipitation extremes except for the duration indices. Averages of projected precipitation extremes over the climatic regions in Canada are projected to increase under RCP4.5. Such increases under RCP8.5 would be amplified due to higher greenhouse gas emissions. The projected changes in total precipitation are dominated by changes in wind velocity and relative humidity (e.g., changes in horizontal water vapor flux that would have significant effects on the occurrence of precipitation in Canada). In addition, the changes in the majority of precipitation extremes are commonly attributed to the changes in the saturation vapor pressure due to warmer temperature as described by the Clausius-Clapeyron equation.