Ice Regime Research Articles

Влияние колебаний стока реки Лены на площадь льда в море Лаптевых

The ice regime of the Laptev Sea has significant changes during the last twenty years. After the changes in the ice regime of the Laptev Sea, the influence of river runoff on the processes of seasonal formation and destruction of sea ice have increased. During the period from 2004 to 2022, the average annual ice area in the Laptev Sea has a positive correlation with a fluctuations of Lena runoff. The high-water content years of Lena has stimulated to the speedup of the ice cover formation process in autumn and the shift of the beginning of ice melting in spring to a later date.

Landsat Analysis of Terraced Thermokarst Lake Variability on Alaska's Coastal Plain

ABSTRACTThermokarst lakes are abundant across the Arctic landscape. Although they are largely understood to form due to thawing permafrost and subsidence, these lakes exist in a variety of forms, shapes, and sizes. Some lakes across the Arctic exhibit shallow subaqueous terraces. The terraces have previously been shown to maintain permafrost beneath them due to the presence of bedfast ice during most of the year, whereas a talik develops beneath the deeper central pool. However, the formation of these terraces and their prevalence across the Arctic are currently unknown. In this study, we mapped the locations of thermokarst lakes and their terraces in the Alaska coastal plain using Landsat imagery. We found that terraces are larger and more abundant in sandy deposits, occupying an average of 40% of the lake area, compared to 20% of the lake area in non‐sandy lithologies. Terraces are most often found on the eastern and western lake shorelines, likely associated with regional wind directions, forming on the long sides of northwest–southeast oriented lakes. We propose a conceptual model for terrace formation in sandy deposits that describes the growth of shallow littoral shelves that protect the eastern and western shorelines from erosion while allowing lake extension in the northwest and southeast directions. Finally, given the close association between bedfast ice, talik extent, and the shallow subaqueous terraces, we suggest that mapping of these relatively stable terraces may provide insights about talik extent across the Arctic coastal region. Continued warming and changes to lake ice regimes are likely to increase talik extent, which may be easily observable by temporal analysis of terrace abundance and extent in widely available remotely sensed imagery.

Assessing the impact of climate change and reservoir operation on the thermal and ice regime of mountain rivers using the XGBoost model and wavelet analysis

AbstractThis study presents an analysis of the influence of climatic conditions and the operation of a dam reservoir on the occurrence of ice cover and water temperature in two rivers (natural and transformed by reservoir operations) located in the Carpathian Mountains (central Europe). The analyses are based on data obtained from four hydrological and two climatological stations. The Extreme Gradient Boosting (XGBoost) machine learning model was used to quantitatively separate the effects of climate change from the effects arising from the operation of the dam reservoir. An analysis of the effects of reservoir operation on the phase synchronization between air and river water temperatures based on a continuous wavelet transform was also conducted. The analyses showed that there has been an increase in the average air temperature of the study area in November by 1.2 °C per decade (over the period 1984–2016), accompanied by an increase in winter water temperature of 0.3 °C per decade over the same period. As water and air temperatures associated with the river not influenced by the reservoir increased, there was a simultaneous reduction in the duration of ice cover, reaching nine days per decade. The river influenced by the dam reservoir showed a 1.05 °C increase in winter water temperature from the period 1994–2007 to the period 1981–1994, for which the operation of the reservoir was 65% responsible and climatic conditions were 35% responsible. As a result of the reservoir operation, the synchronization of air and water temperatures was disrupted. Increasing water temperatures resulted in a reduction in the average annual number of days with ice cover (by 27.3 days), for which the operation of the dam reservoir was 77.5% responsible, while climatic conditions were 22.5% responsible.

Determination of occurrence of atmospheric blockings over the Caspian Sea region in winters of 1959–2022, and influence of them on the ice regime of the Northern Caspian Sea

The ice regime of the Caspian Sea has pronounced influence on the heat and moisture exchange of the reservoir with the atmosphere, the state of the ecosystem, as well as human marine activities, including shipping, fishing, construction of hydraulic structures, etc. Consequently, the development of existing ideas about the causes of changes in the characteristics of the ice regime of such water bodies is actual and socially significant problem of limnology, hydrometeorology, ecology, and navigation. This study was aimed at determination the frequency of occurrence of atmospheric blockings over the Caspian region with standings longer 5 days in winter period of 1959–2022, and investigation of influence of them on the ice regime in the Northern area of the Sea. The following information and data were used: changes in hourly mean values of atmospheric pressure at the sea level, geopotential of isobaric surfaces 850, 500 and 300 hPa, presented in the ERA5 reanalysis; and observational data on air temperature and ice cover from hydrometeorological stations located in the Caspian region of Kazakhstan and Russia. It has been established that in the winter during a long standing of atmospheric blockings the mean daily air temperatures noticeably drop. The values of all the studied characteristics of every atmospheric blocking which occurred in 1959–2022 were estimated as well the influence of them on the ice regime in the North of the Caspian Sea was analyzed. The relationship between a decrease in the frequency of atmospheric blockings (AB), sums of negative air temperatures on its coasts, and the ice cover thickness in the corresponding areas of coastal waters has been revealed in the region. The longer the total AB duration, the lower is the air temperature, and the ice thickness in February is larger.

Sea ice choke points reduce the length of the shipping season in the Northwest Passage

Arctic sea ice has shifted from a perennial (older, thicker ice) to a seasonal (younger, thinner) ice regime, leading to the increasingly common belief that shipping through Canada’s Northwest Passage is becoming more viable. Here, we use the Risk Index Outcome values derived from the Polar Operational Limit Assessment Risk Indexing System and analyze recent changes to shipping season lengths along individual sections of the Northwest Passage routes from 2007 to 2021. Results show that multi-year ice flushed southward from high-latitude regions maintains the so-called choke points along certain route sections, reducing overall shipping season length. There is considerable spatiotemporal variability in shipping season lengths along the southern and northern routes. Specifically, parts of the northern route exhibit a decrease of up to 14 weeks over the 15 years. The variability of shipping season and, in particular, the shortening of the season will impact not only international shipping but also resupply and the cost of food in many Arctic communities, which require a prompt policy response.

Past and future of the Arctic sea ice in High-Resolution Model Intercomparison Project (HighResMIP) climate models

Abstract. We examine the past and projected changes in Arctic sea ice properties in six climate models participating in the High-Resolution Model Intercomparison Project (HighResMIP) in the Coupled Model Intercomparison Project Phase 6 (CMIP6). Within HighResMIP, each of the experiments is run using a reference resolution configuration (consistent with typical CMIP6 runs) and using higher-resolution configurations. The role of horizontal grid resolution in both the atmosphere model component and the ocean model component in reproducing past and future changes in the Arctic sea ice cover is analysed. Model outputs from the coupled historical (hist-1950) and future (highres-future) runs are used to describe the multi-model, multi-resolution representation of the Arctic sea ice and to evaluate the systematic differences (if any) that resolution enhancement causes. Our results indicate that there is not a strong relationship between the representation of sea ice cover and the ocean/atmosphere grids; the impact of horizontal resolution depends rather on the sea ice characteristic examined and the model used. However, the refinement of the ocean grid has a more prominent effect compared to the refinement of the atmospheric one, with eddy-permitting ocean configurations generally providing more realistic representations of sea ice area and sea ice edges. All models project substantial sea ice shrinking: the Arctic loses nearly 95 % of sea ice volume from 1950 to 2050. The model selection based on historical performance potentially improves the accuracy of the model projections and predicts that the Arctic will turn ice-free as early as 2047. Along with the overall sea ice loss, changes in the spatial structure of the total sea ice and its partition in ice classes are noticed: the marginal ice zone (MIZ) will dominate the ice cover by 2050, suggesting a shift to a new sea ice regime much closer to the current Antarctic sea ice conditions. The MIZ-dominated Arctic might drive development and modification of model physics and parameterizations in the new generation of general circulation models (GCMs).

Ice regimes, ice jams, and a changing hydroclimate, Saint John (Wolastoq) River, New Brunswick, Canada

Ice regimes, ice jams, and a changing hydroclimate, Saint John (Wolastoq) River, New Brunswick, Canada

Model Analysis of the Thermal and Ice Regime of a Large Lowland Reservoir: Case Study of the Novosibirsk Reservoir

Model Analysis of the Thermal and Ice Regime of a Large Lowland Reservoir: Case Study of the Novosibirsk Reservoir

Assessment of the impact of dam reservoirs on river ice cover – an example from the Carpathians (central Europe)

Abstract. This paper presents a method for determining the impact of dam reservoirs on the ice cover of rivers downstream of their locations based on a long measurement period (1950–2020) and synthetic-aperture radar (SAR) data. Two rivers and two sets of dam reservoirs located in the Carpathian Mountains (central Europe) were selected for this study. In order to estimate the influence of reservoirs, a logistic regression model was built to describe the relationship between the course of air temperature and the occurrence of ice cover (i.e., total ice cover and border ice) at water gauge cross sections upstream and downstream of the reservoirs. The influence of reservoirs was then defined as the differences between the number of days with ice cover predicted from air temperature and those observed at the water gauge cross sections. Additionally, the extent of the impact of the reservoirs was estimated based on SAR data (Sentinel-1) by identifying river sections downstream of the reservoirs on which total ice cover did not form despite the persistence of very low air temperatures. The study shows that dam reservoirs play an important role in decreasing the incidence of ice cover on rivers. The occurrence of ice cover as a result of reservoir operations could decrease by over 80 % in the sections immediately downstream of the reservoirs. The impact of the reservoir on river ice cover diminishes as the distance from the reservoir increases. Using SAR data, it was estimated that total ice cover did not form in sections 26–60 km downstream of the reservoirs, despite the presence of favorable thermal conditions. Based on the results of the study presented here, it can be assumed that in areas where many dam reservoirs are located, the ice regime of rivers is significantly transformed, which should be taken into account when studying river ice cover. This study also demonstrates that the logistic regression model and SAR data are useful tools for assessing the impact of dam reservoirs on river ice cover.

Ice Shape Convergence in Multistep Ice Accretion Simulations

Local errors in the geometrical description of the ice front are amplified in multistep simulations over conformal meshes due to the coupling of aerodynamics, water impingement, ice accretion, and grid deformation. Small perturbations in the initial phase of ice formation possibly result in dramatically different ice shapes, which can hinder the stability of the multistep procedure. This problem is analyzed by investigating the combined effects of space and time discretization on the ice growth over airfoils and three-dimensional wings. We propose an automatic procedure for selecting the time interval for the update of the aerodynamics and particle impingement. A local growth limiter λ is introduced here to bound the local ice thickness growth to be comparable to the local grid spacing on the surface, resulting in an automatic adaptive time step to be used in the multistep simulation. Examples are provided for three-dimensional cases under both rime and glaze conditions over straight and swept wings. These examples highlight the different accretion mechanisms of the two ice regimes and preliminarily indicate that ice-shape convergence can be achieved for low values of λ.

Monitoring climate change in the marine Arctic

Changes in the temperature regime of the marine Arctic and the influencing factors are considered based on the current knowledge of the causes of climate change and the use of new data sources. In the Arctic, the warming is developing due to such factors as the increase in the transfer of heat and moisture from the low latitudes. This, in turn, drives the feedbacks in the Arctic climate system, increasing the flow of long-wave radiation to the surface due to rising atmospheric water vapor concentrations and slowing down the growth of the sea ice thickness in winter. The increase in the atmospheric heat transfer to the Arctic is associated with changes in atmospheric circulation, in particular, under the influence of ocean surface temperature anomalies, especially in the low latitudes since the bulk of the heat influx from the from solar radiation and anthropogenic forcing is accumulated here. Analyzing the causes of warming in the Arctic in the 1930s and 40s led researchers to the conclusion that the water influx from the North Atlantic is a factor to consider. Therefore, the influx of warm and salty water is also an important influence on the formation of the climate of the marine Arctic today, which should be taken into account when monitoring the temperature and ice regime of this area. Based on the analysis of the characteristics of climate variability in the marine Arctic and its causes, the article examines representative indicators of climate change in the temperature and ice regime of the marine Arctic and the factors influencing them in the present period.

Spatial trend analysis of significant wave heights in the Kara Sea

Over the past decades, the extent of sea ice in the Arctic, including the Kara Sea, has been diminishing. This phenomenon has a direct impact on wind waves as the increased expansion of ice-free water influences wave height. Furthermore, alterations in the ice cover also lead to modifications in atmospheric circulation, necessitating a concurrent analysis of wind and waves to refine the understanding of their interrelationships. In this study, wave modeling data were employed using the WAVEWATCH III model and NCEP/CFSR/CFSv2 reanalyzes. Calculations were performed on a non-structural computational grid. The grid covers the Barents and Kara Seas, as well as the entire northern part of the Atlantic Ocean. The spatial resolution varies from ~ 700 m for the coastal zone of the Kara Sea, to ~ 20 km in the open part of the Kara Sea, covering the period from January 1, 1979 to December 31, 2021. Subsequently, average significant wave heights (SWH), maximum SWH, and the 95th percentile of SWH were computed for each grid node on both monthly and yearly basis. The annual values were analyzed for trends and their significance. Calculations were conducted for both the entire period and ice-free period. Positive trends in annual mean values were observed throughout the sea, with the maximum trend occurring near the boundary with the Barents Sea, barely exceeding 0.2 m/10 years. The northern and northeastern parts of the sea were characterized by significant positive trends of the maximum SWH values. Maximum trend values for the 95th percentile of SWH were also evident in the northern part of the Kara Sea. For the ice-free period, maximum trend values were notable for both the annual mean and the 95th percentile of SWH in the northern part of the sea (maximum trend values are approximately 0.25 m/10 years and 0.5 m/10 years, respectively). Significant positive trends in the annual mean SWH were characteristic of the southern part of the sea, while the largest and significant trends for maximum wave heights were observed in the northeast. The assessment of the contribution of wind and ice regimes to the variability of wind waves remains a subject of discussion.

Assessment of atmospheric circulation impacts on the Caspian Sea level and ice regime

The research aimed to assess the influence of atmospheric processes in the Northern Hemi-sphere’s Atlantic-European Sector on the Caspian Sea level based on the data for the days with Wangenheim-Girs atmospheric general circulation forms. The inputs covered the time period from 1900 to 2022. The information on the sea level, precipitation and ice events were harvested from 22 observation points in Kazakhstan and Russia. The statistical and comparative analysis as well as the climate change assessment within the framework of the study pointed to a stable correlation between the sea level and atmospheric circulation; re-vealed certain patterns reflected in precipitation distribution and frequency of moisture defi-cient and excessive years. The research also identified that the climatic changes have al-tered the sea’s ice regime, with the maximum ice thickness decreasing by 13-28 cm depend-ing on a specific water area. In addition to ice thickness variation, the recent decades show an increased frequency of moderate and mild winters, and the shift of the main glaciation dates, i.e. a stable ice cover forming later, the date of fixed maximum ice thickness observed in mid-February, the date of complete ice clearing observed in early-mid March, and the freezing period being shorter.

Warming Climate-Induced Changes in Lithuanian River Ice Phenology

Due to rising surface air temperatures, river ice is shrinking dramatically in the Northern Hemisphere. Ice cover during the cold season causes fundamental changes in river ecosystems and has important implications for nearby communities and industries. Changes caused by climate warming, therefore, affect the sustainability of key resources, livelihoods, and traditional practices. Thus far, too little attention has been paid to research into the phenomenon of river ice in the Baltic States. Since the observational data of the last sixty years are currently available, we took advantage of the unique opportunity to assess ice regime changes in the gauged rivers by comparing two climatological standard normals. By applying statistical methods (Mann–Kendall, Pettitt, SNHT, Buishand, von Neumann, and Wilcoxon rank sum tests), this study determined drastic changes in ice phenology parameters (freeze-up date, ice break-up date, and ice cover duration) of Lithuanian rivers in the last thirty-year period. The dependence of the selected parameters on local climatic factors and large-scale atmospheric circulation patterns was identified. It was established that the sum of negative air temperatures, as well as the North Atlantic Oscillation, East Atlantic, and Arctic Oscillation indices, have the greatest influence on the ice regime of Lithuanian rivers.

Наводнения периода ледовых явлений на реках Северо-Западного федерального округа

The purpose of the study is to study the intra-annual distribution of water levels, taking into account ice conditions. An assessment of the recurrence of ice phenomena at hydrological stations with a high frequency of exceeding the level of a dangerous hydrological phenomenon (DHP) and an unfavorable hydrological phenomenon (UHP) was carried out. The values of the value of the excess of the highest water level over the established critical water levels of the DHP or UHP have been calculated. It has been revealed that on the territory of the studied region, the excess of the marked and DHP occurs not only during spring floods, ice jams, but also ice movements, autumn and spring ice drift, and even under non-compact freezing. Underestimation of the level and ice regime significantly complicates the implementation of measures to prevent and minimize the negative consequences and damage from dangerous ice hydrological phenomena

The ice regime of the northeastern Russia

Transport links and provision of hard-to-reach settlements and mining enterprises play an important role in the economic development of the Arctic regions. In winter, winter roads are used as transport arteries; their mode of operation depends on the characteristics of the ice. Winter roads are used in Russia, Canada, USA, Finland, and China. Due to climate warming, the timing of the formation of ice cover on rivers is shifting to later times, and in the spring the ice is destroyed earlier. This could affect the delivery of vital supplies to remote regions. According to recent forecasts, it is assumed that heavy vehicles will not be able to use winter roads by the end of the 21st century. The purpose of the study is to analyze changes in the characteristics of ice cover on the rivers of the Northeast of Russia. To do this, a series of data was collected for the period 1940–2018 on the thickness of the ice cover at 80 hydrological stations located in the basins of the Yana, Indigirka, Kolyma rivers, rivers of the Chukotka Peninsula and the Sea of Okhotsk basin. The catchment areas range from 18.3 to 635,000 km2, and the duration of the continuous series ranges from 2 to 67 years. Three statistical nonparametric tests (Mann-Kendall, Pettitt and Theil-Sen) were used for evaluation. The following characteristics were considered: the maximum ice thickness and the date of its formation, the dates when the ice thickness reached 60 and 90 cm. During the period under review, the maximum ice thickness decreased by an average of 40 cm, while the date of reaching the maximum values remained almost unchanged. The period for the formation of river ice with a thickness of 60 and 90 cm, necessary for the passage of cars and trucks, respectively, has shifted by almost a month. The start date of freeze-up occurs on average 3–4 days later, and the end date of freeze-up occurs 5–8 days earlier. On average, the duration of freeze-up decreased by 5–15 days. The results obtained must be taken into account when drawing up the work schedule for winter roads. This is especially important for regions where communication between populated areas and mining enterprises is possible only through river arteries.

Long-term forecasting methods of dates of ice break-up and disappearance at the Dnipro Cascade Reservoirs by teleconnection indicators

Long-term forecasting of the ice regime at the Dnipro Cascade Reservoirs is very important, first of all, for the operation of hydroelectric power stations. In addition, such forecasts also ensure the work of other sectors of the economy, namely shipping, fisheries, municipal engineering, etc. At present, the Department for hydrological forecasting of the Ukrainian Hydrometeorological Center uses techniques developedin the middle and in thesecond half of the 20th century to compile long-term forecasts and advices about the ice regimeof water bodies of Ukraine. These techniqueswere developed only for rivers;for reservoirs,they are currently lacking.
 The main objective of our research is to develop methods for long-term forecasting of ice break-up and disappearance at the Dnipro Cascade Reservoirs by teleconnection indicators. The research was based on the recordsfor 35 water gauges located on 6 reservoirs of the Dnipro Cascade, including the destroyed Kakhovka reservoir. The dates of the ice break-up and disappearance were used for the period from the beginning of observations at each water gauge to 2020. Moreover, the teleconnection indicators were used, namely 34 atmospheric indices, sea surface temperature indices, teleconnection indices and patterns determined by the National Weather Service (NWS) of the National Oceanic and Atmospheric Administration of United States of America (NOAA USA).
 Methods of the long-term forecasting of the ice break-up and disappearance at the reservoirs of the Dnipro Cascade have been developed by searching for the best correlation or regression relationship between dates and teleconnection indicators. The probable of accepted errorsof the developed methods are in the range of 62—71 %, which corresponds to satisfactory method quality that makes it possible to recommend them for use.

Влияние опасных гидрометеорологических явлений на эксплуатацию транспортного перехода через Керченский пролив

The article considers the natural and climatic conditions of the Kerch Strait, the Taman Peninsula and the Kerch Peninsula through which passes the transport crossing that connects the Republic of Crimea with the Russian mainland. The paper reflects the main features of the formation of dangerous hydrometeorological phenomena in the Kerch Strait. Hydrometeorological conditions of formation of ice and wind-wave regimes and other dangerous hydrological and hydrometeorological phenomena in the Kerch Strait are highlighted based on the coastal and expedition observations, measurements of currents at automatic buoy stations, numerical modeling of water dynamics in the Kerch Strait for different types of atmospheric effects on the grid with high spatial resolution. The research shows that in the coastal zone and on the Kerch Strait water area periodically there are dangerous hydrometeorological phenomena, such as ice blockages on the bridge piers, strong storm or hurricane wind, heavy precipitation, fogs, which significantly worsen the visibility and complicate marine cargo transportation in the Strait, thunderstorms and tornados. The data presented in this work may be the basis for the assessment of the current state of the environment within the environmental support of the projects, as well as the subsequent ice and hydrometeorological monitoring in the area of the Crimean bridge.

Interannual variability of ice cover across Davis Strait and the Labrador Sea for the period from 1979 to 2023

In conditions of rapid development of trade and transport communications, the issue of navigation through ice regime zones became of greater importance. In particular, reduction of the area of ice cover in the Canadian Arctic because of global warming opens up favourable prospects for further development of maritime shipping in this zone. Considering that the routes through the Northwest Passage are the shortest ones of all the routes connecting the Atlantic and Pacific oceans, it is clear that all aspects of this topic are of great importance and relevance. This especially applies to the aspects dedicated to studying the characteristics of appearance, formation, concentration, physical characteristics, trajectory of ice movement and forecasting the area of the ice cover in a given zone, i.e. the characteristics affecting the conditions of ice navigation and serving as determining factors in terms of navigation safety.
 The research examines some of these issues, namely the spread of the ice cover during the period of its maximum formation across Davis Strait and the Labrador Sea (where the routes through the Northwest Passage start) and the establishment of statistical relations between the ice spread and the temperatures of surface water and surface air. The research method to be used: synoptic-climatic and statistical analysis of numerical series of ice cover deviations from its average limit as of April 15 over the period of 1979-2023 within the zone in study.
 Based on the set goal, the study processed raw data on distribution of ice cover across Davis Strait and the Labrador Sea for the period of 1979-2023 and completed its statistical analysis. The results of the analysis showed presence of a statistically significant negative trend and cyclical fluctuations with periods of 3-6, 9, 10 and 13 years in relation to the interannual variability of ice cover distribution for the studied period. Positive trends are also observed in the interannual variability of surface water temperature and surface air temperature. After bringing the original series to a quasi-stationary form, a correlation analysis of the relationships between the ice cover distribution and the temperature of water and air was carried out. The results of the analysis determined zones and points with statistically significant correlation coefficients between them during the year. It turned out that the highest values of coefficients are observed from December to March, and the maximum one occurs in March.
 Systematization and analysis of the ice field across Davis Strait and the Labrador Sea during the period of maximum development made it possible to establish that the spread of ice between 60° and 55° north parallels was the most stable during the studied period, and the least stable was observed in the area below 55° north parallel.
 The results of the conducted research open up prospects for development of methods for forecasting the distribution of ice cover across Davis Strait and the Labrador Sea. This will make ice navigation in this area safer.

River Ice Regime Recognition Based on Deep Learning: Ice Concentration, Area, and Velocity

The real-time derivation of the concentration, area, and velocity of river surface ice based on camera imagery is essential for predicting the potential risks related to ice blockages in water routes. The key lies in the continuous tracking and velocity measuring of river ice, and reliable ice motion detection is a prerequisite for the dynamic perception of tracking targets. Previous studies did not utilize motion tracking for measuring ice velocity, and particle image velocimetry and feature point matching were used. This study aimed to use deep learning methods to address the challenging problems of deriving the ice concentration, area, and velocity based on camera imagery, and the focus was on measuring the ice velocity and drawing trajectories using the particle video tracking algorithm. We built a dataset named IPC_RI_IDS and collected information during the ice cover break-up process in the Nenjiang River (China). Our suggested approach was divided into four steps: (1) image preprocessing, where the camera image was calibrated to real-world coordinates; (2) determining the ice and water pixels in the camera image using the lightweight semantic segmentation network and then calculating the ice concentration and area; (3) enhancing and optimizing motion detection using the semantic segmentation results; and (4) adapting the particle video tracking algorithm to measure ice velocity using the proposed tracking points generation strategy. Finally, we analyzed the surface ice data in the study area and attempted to predict the stage of the ice break-up process to provide support for the real-time short-term forecasts of ice floods.