Effects of changing freshwater ice regimes

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Climate Change/Variability and Freshwater-Ice Systems Freshwater ice is an integral component of cold-regions lakes and rivers and an important modifier of related physical, chemical and biological processes. Although repeated concerns have been expressed about the potential impacts of climate change on ice-covered systems (e.g., assessments for the Intergovernmental Panel on Climate Change and the Arctic Council (Arctic Climate Impact Assessment; Snow Water Ice Permafrost in the Arctic), our current knowledge base makes it difficult to predict the nature and magnitude of the effects of a changing climate on ice-covered systems. This project will focus on filling some of our most important knowledge gaps by addressing two major research themes: 1) extreme ice-induced hydrologic events on rivers (e.g., floods and droughts); and 2) the impact of changing ice-covers on lake water chemistry that controls biological production/diversity. The objective of the 1st theme is to establish the controlling characteristics and significance of extreme hydrologic events created by river ice in the major hydro-climatic regions of Canada. Although changes to extreme events are a major concern regarding future climate change, the importance of ice-induced extreme floods has never been fully quantified beyond a collection of disparate case studies. Previous research conducted by this researcher is leading to a multi-regional national classification of the seasonal/temporal trends in, and relative magnitude (compared to open-water events) of, spring break-up floods across Canada. Based on a unique data-archive assembled by this applicant, this research will: i) quantify temporal and spatial trends in river freeze-up levels across Canada, ii) evaluate their effect on subsequent break-up flooding; iii) quantify similar trends in ice-induced low flows, in the occurrence and magnitude of mid-winter break-up events. A related set of objectives is to define the hydro-climatic controls that have led to the historical trends in such ice-affected hydrologic events, and to project what changes will occur to these trends, under future climate change. Moreover, it will also indicate the regional locations and severity of projected future occurrences. Given the large economic effect that can occur from break-up flooding, the current and planned flow regulation of cold-regions rivers (e.g., for hydro-electric production), and the importance of winter water abstraction during the time of flows (e.g., for increasing industrial development), the results of this research will provide invaluable tools to be used in flow regulation, water-supply management, and flood forecasting. The 2nd project theme will focus on how a changing climate is affecting the composition of lake-ice covers, and specifically on ice-cover types important to lake ecology. Previous research by this applicant has quantified how lake-ice thickness across North America and the Northern Hemisphere will be altered under a future climate. This new research will extend the focus to the role of changes in hydro-climatic conditions that modify ice-cover composition, which affects underwater light regimes, thermal conditions, and dissolved oxygen levels. The numerical model MyLake used in the previous research will be modified to include key algorithms that model all such changes. Test data from multi-sensor lake buoys deployed at high-latitude sites (e.g., as part of Canada’s program to develop the Canadian High Arctic Research Station) will be used for model validation. This second theme will also make projections of future changes to ice-cover composition, water-quality conditions, related biological productivity, and their effect on key trace-gas fluxes (e.g., carbon and methane).