Characterizing the temperature and precipitation covariability over Canada

Abstract

Changes in the regional characteristics of temperature and precipitation can intensify the occurrence and severity of extreme events such as rain-on-snow-induced flooding, droughts and wildfires. Analyzing these climate variables in isolation without considering their interdependencies might result in severe underestimation of their combined effects. In addition, the assumption of linearity between temperature and precipitation does not represent the real physical processes that govern these climate variables. In this study, copula functions are used to describe the joint behaviour of temperature and precipitation across 15 ecozones of Canada at multiple temporal scales. The Clausius-Clapeyron (CC) relation is investigated using daily records to quantify changes in extreme precipitation with temperature increases. In addition, using historical records, dating back to 1910s, temporal changes in the dependence structure across southern Canada are analyzed using a non-stationary framework. Results show clear signs of accelerated warming and wetting over northern Canada while strong evidence of hot and dry conditions is found in the Prairie provinces. Analyses over seasonal and monthly scales indicate increases in warm-wet and hot-dry conditions in winter and summer, respectively. Non-stationary analyses reveal shifts towards warm and wet climate conditions for the majority of southern Canada. Considerable deviations from the theoretical CC scaling rate of 6.8% is observed for extreme precipitation over parts of Canada with super-CC scaling rates observed in northern Canada and sub-CC scaling rates in the majority of southern Canada.