Assessing and predicting the severity of mid-winter breakups based on Canada-wide river ice data

Mid-winter breakups (MWBs), consisting of the early breakup of the winter river ice cover before the typical spring breakup season, are becoming increasingly common events in cold region rivers. These events can lead to potentially severe flooding, while also altering the expected spring flow regime, yet data on these events is limited. In this study, a newly released Canadian River Ice Database (CRID), containing river ice data from 196 rivers across Canada obtained from time series analysis, was used to analyse these MWBs on a previously impossible national scale. The CRID data was combined with the Natural Resources Canada (NRCan) gridded daily climate dataset to identify a list of potential hydrologic and climatic drivers for MWB events. Techniques such as correlation analysis, Least Absolute Selection Shrinkage Operator (LASSO) regression, and input omission were combined to select 20 key drivers of the severity of MWB events. A random forest model that was trained with these drivers using data-driven modelling techniques successfully classified the MWBs as either low, medium, or high severity, achieving an overall accuracy of 80%. A new threshold for the prediction of MWB initiation based on climatic conditions was subsequently proposed through the use of optimization via an exhaustive grid search and its accuracy in identifying MWBs exceeded those proposed by previous studies. The new threshold used in conjunction with the random forest model provide valuable tools for both the prediction of MWBs and the assessment of their potential severity.