Regional climate change trends and uncertainty analysis using extreme indices: A case study of Hamilton, Canada

Abstract This study aims to provide a deeper understanding of the level of uncertainty associated with the development of extreme weather frequency and intensity indices at the local scale. Several different global climate models, downscaling methods, and emission scenarios were used to develop extreme temperature and precipitation indices at the local scale in the Hamilton region, Ontario, Canada. Uncertainty associated with historical and future trends in extreme indices and future climate projections were also analyzed using daily precipitation and temperature time series and their extreme indices, calculated from gridded daily observed climate data along with and projections from dynamically downscaled datasets of CanRCM4 and PRECIS, and the statistically downscaled CIMP5 ensemble. A bias correction technique was applied to all raw daily temperature and precipitation time series prior to calculation of the indices. All climate models predicted increasing trends for extreme temperature indices, maximum 1-day and 5-day precipitation (RX1day and RX5day), total wet day precipitation (PRCPTOT), very heavy precipitation days (R20mm), Summer Days (SU), and Tropical Nights (TR) and decreasing trend for Forest Days (FD) and Ice Days (ID) in 2020s, 2050s, and 2080s compared to present. CanRCM4 model did consistently project values in the upper range of the CMIP5 ensemble while the PRECIS ensemble was more in-line with the CMIP5 mean values. This difference may however be a function of different emission scenarios used.