  The Peace-Athabasca Delta (PAD) of northwestern Alberta is one of the largest
inland freshwater deltas in the world, laying at the confluence of the Peace
and Athabasca Rivers. The PAD is recognized as a having unique ecological
significance and periodic ice jam flooding from both rivers is an important
feature of its current ecology. Past studies have debated whether a change in
ice jam flood (IJF) frequency on the Peace River has recently occurred, and
what factors might be driving any perceived changes. This study contributes to
this debate by addressing two questions: (1) what factors are most predictive
of Peace River IJFs, and (2) how might climate change impact IJF frequency?
This work starts with a physically-based conceptual model of the necessary
conditions for a large Peace River IJF, and the factors that indicate whether
those conditions are met. Logistic regression is applied to the historical
flood record to determine which combination of hydroclimatic and riverine
factors best predict IJFs and the uncertainty in those relationships given the
available data. Winter precipitation and temperature are most predictive of
Peace River IJFs, while freeze-up elevation contains little predictive power
and is not closely related to IJF occurrence. The best logistic regression
model is forced with downscaled climate change scenarios from multiple climate
models to project IJF frequency for a variety of plausible futures. Parametric
uncertainty in the best logistic regression model is propagated into the
projections using a parametric bootstrap to sample many plausible statistical
models. Although there is variability across emissions scenarios and climate
models, all projections indicate that the frequency of Peace River IJFs is
likely to decrease substantially in the coming decades, and that average
waiting times between future IJFs will likely surpass recent experience.
