Development of relevant and plausible water supply sequence scenarios for application to adaptive management of Lake Ontario outflows

Abstract:

Record or near record high net basin supply to Lake Ontario, along with very high Lake Erie outflows and record high Ottawa River flows, led to historic flooding events on Lake Ontario and the St. Lawrence River in both 2017 and 2019. These flooding events occurred during the wettest 5 years on record in the Great Lakes basin (since 1895), and are part of an ongoing event of extremely high water levels across the Great Lakes basin resulting in significant damages due to flooding and erosion. With record-setting conditions occurring in two of the last four years, the need for adaptive management of Lake Ontario outflows has received significant attention. This presentation will describe efforts to develop relevant and plausible 1- to 3- year water supply scenarios for application to adaptive management of Lake Ontario outflows. Although the Lake Erie outflows, Lake Ontario net basin supply, and Ottawa River flows were within the range of stochastically generated sequences used to develop what is now regulation Plan 2014 for Lake Ontario outflows, these recent extremes suggest a need to re-evaluate the assumption of stationarity that is inherent to the stochastic sequence generation and establish a new methodology for identifying plausible scenarios. This work contributes to a larger effort by the Great Lakes Adaptive Management Committee to provide an expedited review of regulation Plan 2014. Approaches under consideration in this analysis include (1) redevelopment of stochastic sequences that incorporate the most recent extremely wet years, (2) application of regional climate modeling, and (3) extension of existing seasonal to interannual forecast tools. The analysis will result in recommended plausible sequences for use in future regulation plan evaluation efforts by the Great Lakes Adaptive Management Committee, as well as recommended analyses to produce plausible scenarios over the long range.