Theme B : Statistical extremes allowed by fine mesh and land-atmosphere feedbacks

Associated with global warming resulting from anthropogenic emissions of greenhouse gases and aerosols (GHGA), changes in temperature extremes and increases in intense precipitation events are amongst the more robust climate-change signals in the observed weather records, as well as in model projections for the future (Kharin et al., 2007, 2012; Seneviratne et al., 2012). Questions about extremes are highly topical both scientifically and from an impacts perspective. Intense precipitation events and temperature extremes have substantial impacts on ecosystems, infrastructure, and the health and safety of Canadians. Climate models such as GCMs and RCMs are the primary tools used to study anticipated climate changes associated with specific time-evolving emissions scenarios for anthropogenic GHGA. The coarse spatial resolution of GCMs does not adequately represent mesoscale processes and fine scale topographic features, which is a severe limitation for impact and adaptation studies. The higher spatial resolution of RCMs, compared to GCMs, allows for greater realism of physiographic forcing and finer-scale atmospheric dynamics; they thereby represent a potentially more suitable tool for adequately simulating processes responsible for precipitation and temperature extremes as required for regional impact and adaptation studies.

This theme will document the ability of high-resolution RCMs to simulate extreme temperature and precipitation events, and their links to circulation variations and land-atmosphere coupling, both incurrent and future climates. The analysis will make full use of standard extreme indices and statistical extreme value theory.

Research Projects

The ability of GCMs participating in CMIP5 (Coupled Model Intercomparison Project Phase 5) to simulate climate extremes has recently been evaluated by Sillmann et al. (2012a, b). The CMIP5 models were found to simulate temperature extremes about as well as previous CMIP3 models, but demonstrate improvement for precipitation extremes. Further, the study of Murdock et al. (2012), using reanalysis-driven RCMs participating in NARCCAP, has revealed smaller biases in temperature extremes in the Columbia River Basin.

Will there be more floods/droughts in future climate? What is the role of soil moisture-atmosphere coupling in modulating the extreme temperature/precipitation extremes over Canada? Climate change induced changes in the frequency and magnitude of floods and droughts could be detrimental to Canadians and therefore the study of climate change impacts on floods and droughts is important to ensure safety of Canadians, as well as for better management of freshwater resources and planning of appropriate adaptation strategies. Floods and droughts are multivariate events.

Output comparisons between different model versions are ubiquitous during climate model development, model tuning and while performing numerical experiments. As such, statistical tests of significance are fundamental tools to help us judge the merits of a given model modification. Despite that RCM studies are becoming a mature branch of climate modelling, surprisingly little has been done to define the most appropriate battery of these tests.