Climate change is leading to river ice thinning and shorter ice cover durations, posing significant risks to travel safety and ecosystem health. Due to limited in-situ observations in Alaska, models and remote sensing are employed to understand changing river conditions. This study conducts a comparative evaluation of statistical, machine learning, and remote sensing techniques to assess river ice presence and thickness across Alaska and the Yukon River basin. Sentinel-1 synthetic aperture radar data, climate model outputs, and in-situ river ice observations throughout Alaska are used to evaluate the regional applications of these techniques for determining river ice phenology and thickness. Our analysis reveals that ice presence can be accurately identified using Sentinel-1 images and climate data processed through machine learning models, achieving high accuracy across Alaska. Predicting ice break-up and freeze-up with these methods also yields high accuracy, with a root mean square error (RMSE) of 5.3 and 15.0 days, respectively, for machine learning at out-of-sample locations. Statistical, machine learning, and remote sensing techniques each demonstrated similar performance in determining ice thickness, with RMSEs ranging from 18 to 23 cm for out-of-sample years or locations. However, an ensemble of these methods significantly reduced the RMSE to 13 cm. Using the best-performing models, we generated high-resolution estimates of river ice phenology and thickness for major rivers in Alaska. The ensemble river ice thickness methods and the machine learning ice presence model show promise for widespread application in diverse regions, facilitating environmental monitoring and enhancing river ice safety.

The notion of convergent and transdisciplinary integration, which is about braiding together different knowledge systems, is becoming the mantra of numerous initiatives aimed at tackling pressing water challenges. Yet, the transition from rhetoric to actual implementation is impeded by incongruence in semantics, methodologies, and discourse among disciplinary scientists and societal actors. This paper confronts these disciplinary barriers by advocating a synthesis of existing and missing links across the frontiers distinguishing hydrology from engineering, the social sciences and economics, Indigenous and place-based knowledge, and studies of other interconnected natural systems such as the atmosphere, cryosphere, and ecosphere. Specifically, we embrace ‘integrated modeling’, in both quantitative and qualitative senses, as a vital exploratory instrument to advance such integration, providing a means to navigate complexity and manage the uncertainty associated with understanding, diagnosing, predicting, and governing human-water systems. While there are, arguably, no bounds to the pursuit of inclusivity in representing the spectrum of natural and human processes around water resources, we advocate that integrated modeling can provide a focused approach to delineating the scope of integration, through the lens of three fundamental questions: a) What is the modeling ‘purpose’? b) What constitutes a sound ‘boundary judgment’? and c) What are the ‘critical uncertainties’ and how do they propagate through interconnected subsystems? More broadly, we call for investigating what constitutes warranted ‘systems complexity’, as opposed to unjustified ‘computational complexity’ when representing complex natural and human-natural systems, with particular attention to interdependencies and feedbacks, nonlinear dynamics and thresholds, hysteresis, time lags, and legacy effects.

In this research, we explore whether a dendrogeomorphological assessment of tree scarring can accurately summarize past ice-jam flooding events occurring at a given reach of a river. A sample site was chosen with a history of ice-jam flooding located in close proximity to a river gauge station. Samples were collected along a 200-metre stretch of riverbank to capture the variation in elevations and possible different ice-jam flooding events. Disk samples were collected from trees with visual scarring evidence that indicated they had endured a past ice-jam event. Tree cores from an adjacent stand were collected to create a master chronology for each of the sampled species. Tree disks and cores were analyzed under a microscope using a Velmex stage system, then visually and statistically crossdated using the program COFECHA. Based on the last year of tree growth, years of individual injury events were established. The years of injury event dates were compared against the years of highest instantaneous maximum water elevations from gauged river data. The two data sets correlated, as years with highest recorded injury event dates were also the years of highest instantaneous water level elevations. The most common years of injury event dates were directly reflected in the top five years of highest river instantaneous water level elevations. In addition, the year of 2020 had the highest water elevations in the past 27 years, which was again reflected in the dendrogeomorphological data as the injury event year of 2020 was recorded on over 90% of the sampled tree disks. The correlation found between the gauged river data and the dendrogeomorphological data strongly suggests that past ice-jam flooding event dates can accurately be determined through the analysis of trees in riverbank stretches that have been impacted by ice-jams. The relationship of the gauged river data to the dendrogeomorphological data will therefore allow researchers to determine ice-jam site histories in remote areas where no gauged data exists. The site histories can provide information such as the years or heights that past ice-jam flooding occurred, which could then be used in ice-jam flooding hazard assessments.

Cold regions provide water resources for half the global population yet face rapid change. Their hydrology is dominated by snow, ice and frozen soils, and climate warming is having profound effects. Hydrological models have a key role in predicting changing water resources, but are challenged in cold regions. Ground-based data to quantify meteorological forcing and constrain model parameterization are limited, while hydrological processes are complex, often controlled by phase change energetics. River flows are impacted by poorly quantified human activities. This paper reports scientific developments over the past decade of MESH, the Canadian community hydrological land surface scheme. New cold region process representation includes improved blowing snow transport and sublimation, lateral land-surface flow, prairie pothole storage dynamics, frozen ground infiltration and thermodynamics, and improved glacier modelling. New algorithms to represent water management include multi-stage reservoir operation. Parameterization has been supported by field observations and remotely sensed data; new methods for parameter identification have been used to evaluate model uncertainty and support regionalization. Additionally, MESH has been linked to broader decision-support frameworks, including river ice simulation and hydrological forecasting. The paper also reports various applications to the Saskatchewan and Mackenzie River basins in western Canada (0.4 and 1.8 million km2). These basins arise in glaciated mountain headwaters, are partly underlain by permafrost, and include remote and incompletely understood forested, wetland, agricultural and tundra ecoregions. This imposes extraordinary challenges to prediction, including the need to overcoming biases in forcing data sets, which can have disproportionate effects on the simulated hydrology.