Assessment of summer extremes and climate variability over the North-East of North America as simulated by the Canadian Regional Climate Model

The present study focuses on the evaluation and comparison of the ability of two versions of the Canadian Regional Climate Model (CRCM) driven by re-analyses (NCEP–NCAR) to reproduce the observed extremes and climate variability in summer (1961–1990). The analysed variables are daily precipitation, minimum and maximum temperatures over three regions located in north-eastern North America that are characterized by different topography and observation density. The validation has been performed with multiple climate extreme indices characterizing the frequency, intensity and duration of precipitation and temperature events. The assessment of the ability of the CRCM is done through an in-depth analysis of the statistical distribution, performance scores and interannual variability of extreme indices. The reference database has been constructed by kriging the daily observed data from local meteorological stations onto the CRCM 45-km grid. The vast majority of results over the three regions show that, with respect to the previous (i.e. 3.7.1) CRCM version, the latest version (4.1.1) improves in general the simulated extreme events. In particular, the intensity of extreme hot summer temperature, diurnal temperature range, wet days occurrence, seasonal dry spell, and to a lesser extent extreme cold summer temperature and heavy rainfall. The study suggests that improvements in the simulated extremes in the latest version are due mainly to the introduction of the new land surface scheme (CLASS 2.7), with a more sophisticated representation of the soil moisture content. This suggests the importance of surface processes parameterization as a potential cause of errors in simulated extremes