Low-frequency variability in Canadian hydroclimate

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Freshwater is our most vital natural resource and it is under severe threat globally due to global warming and direct human impacts. I study Canadian freshwater availability, including floods and droughts, for the last two millennia, present and near future. My long-term objective is to better understand multi-decadal and multi-centennial water variability and apply this long-term baseline to better estimate the probabilities of floods, droughts and other related extreme events. This type of low-frequency variability is just at or beyond the range of instrumental records, yet its comprehension is essential. For these baselines, we need the longest (i.e. centennial or longer) and most accurate water records. In the near future, Canada will be affected by the extremes of floods and droughts becoming even more extreme due to global warming. Hence an initial present-day underestimation of their recurrence probabilities due to using too short baseline records will prove costly. As well, understanding low-frequency variability is needed for the regional detection of global warming. When we attempt to attribute an observed hydrological change to global warming, we have to know what the natural multi-decadal to multi-centennial variability is, because such low-frequency variability can be easily mistaken for the effects of global warming. Sources of natural variability include atmosphere-ocean climate oscillations such as the El Nino-Southern Oscillation and Pacific Decadal Oscillation. In my long-term baseline studies, I use the longest observed records, and then go back beyond them, using records derived from tree-ring widths or pollen preserved in lake sediments and sampled at high resolution. The short-term objectives of my proposal are: 1) to examine central, northern and Maritime Canadian river records for the impacts of the climate oscillations on floods, because leaving these out may cause underestimation of flood return intervals and heights; 2) to better estimate the probabilities of droughts and wet periods in southern Alberta and southeastern Québec, using long baselines from millennial-length river reconstructions based on tree-rings, carefully constructed to capture low-frequency variability; 3) to examine changes in moisture and temperature, and consequently forest composition in southeastern Québec over the last 1000 years via pollen preserved in lake sediments and sampled at high-resolution; and 4) to use sedimentary pollen to extend fire records back for a millennium in central Saskatchewan (fire and drought are closely linked). This research program is novel as it studies water variability at both multi-decadal and multi-centennial scales, using the widest possible range of data sources, and focuses on the costly impacts of both droughts and floods in Canada. It will allow significant progress in more resilient water management in the presence of global warming.