B2. Hydrological floods and droughts in future climate

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. For example, a flood event is generally characterized in terms of flood peak, volume and duration, and similarly a drought event is characterized in terms of drought duration, intensity and severity. These characteristics of floods and droughts are often perceived as correlated random variables. Historically, characteristics of these extreme events have been modelled within a probabilistic domain using a univariate approach that can only provide limited information about their multivariate aspects since it does not exploit dependence of flood and drought characteristics. A multivariate approach based on copulas is a natural paradigm to exploit dependencies of various characteristics of floods and droughts and to produce more meaningful return intervals of various combinations of characteristics. Some preliminary investigation using Quebec watersheds as a test bed was performed within a Collaborative Research and Development (CRD) project funded by NSERC and Hydro-Qu├ębec/Ouranos. It is proposed here to undertake assessment of climate-change impacts on characteristics of floods and droughts for the whole of Canada at watershed level within a multivariate framework, using high-resolution simulations. It is expected that some of the biases in simulated streamflows with respect to timing and magnitude at coarse model resolution noted for Quebec watersheds can be overcome at high-resolution and with the land-surface related development work proposed under Theme C.

This project will also explore the role of soil moisture-atmosphere coupling on modulating extremes. A number of studies suggest an increase in the frequency and intensity of temperature and precipitation extremes over the Canadian high-latitudes (e.g. Mladjic et al., 2011; Separovic et al., 2012b). The physical mechanisms underlying such changes may relate to changes in large-scale circulation and/or changes in processes such as soil moisture-atmosphere interactions. Jaeger and Seneviratne (2011) studied the impact of soil moisture-atmosphere coupling on European climate extremes and trends in RCM simulations. Soil moisture-atmosphere interactions were found to have significant effects on temperature extremes in their study. The hypothesis that surface moisture availability provides an additional feedback mechanism (Findell and Eltahir, 1997), helping to maintain extreme wet or dry conditions was studied by Pan et al. (1995) for the US flood of 1993 as well as the drought of 1988. They showed that when all other climatic variables were simulated as observed in each of the two years of interest, extreme changes in the surface moisture conditions significantly altered summer precipitation. It is proposed here to investigate the role of land-atmosphere coupling, on temperature and precipitation extremes, over Canada, using CRCM5.