Climatic changes to freshwater ice in the Arctic are projected to produce a variety of effects on hydrologic, ecological, and socio-economic systems. Key hydrologic impacts include changes to low flows, lake evaporation regimes and water levels, and river-ice break-up severity and timing. The latter are of particular concern because of their effect on river geomorphology, vegetation, sediment and nutrient fluxes, and sustainment of riparian aquatic habitats. Changes in ice phenology will affect a wide range of related biological aspects of seasonality. Some changes are likely to be gradual, but others could be more abrupt as systems cross critical ecological thresholds. Transportation and hydroelectric production are two of the socio-economic sectors most vulnerable to change in freshwater-ice regimes. Ice roads will require expensive on-land replacements while hydroelectric operations will both benefit and be challenged. The ability to undertake some traditional harvesting methods will also be affected.

Paleolimnological evidence from some Arctic lakes suggests that longer ice-free seasons have been experienced since the beginning of the nineteenth century. It has been inferred from some additional records that many Arctic lakes may have crossed an important ecological threshold as a result of recent warming. In the instrumental record, long-term trends exhibit increasingly later freeze-ups and earlier break-ups, closely corresponding to increasing air temperature trends, but with greater sensitivity at the more temperate latitudes. Broad spatial patterns in these trends are also related to major atmospheric circulation patterns. Future projections of lake ice indicate increasingly later freeze-ups and earlier break-ups, decreasing ice thickness, and changes in cover composition, particularly white-ice. For rivers, projected future decreases in south to north air-temperature gradients suggest that the severity of ice-jam flooding may be reduced but this could be mitigated by changes in the magnitude of spring snowmelt.

Freshwater ice dominates the Arctic terrestrial environment and significantly impacts bio-physical and socio-economic systems. Unlike other major cryospheric components that either blanket large expanses (e.g., snow, permafrost, sea ice) or are concentrated in specific locations, lake and river ice are interwoven into the terrestrial landscape through major flow and storage networks. For instance, the headwaters of large ice-covered rivers extend well beyond the Arctic while many northern lakes owe their genesis to broader cryospheric changes. The effects of freshwater ice on climate mostly occur at the local/regional scale, with the degree of influence dependent on the magnitude, timing, location, and duration of ice cover, and the size of the water body. Freshwater-ice formation, growth, decay, and break-up are influenced by climatic variables that control surface heat fluxes, but these differ markedly between lakes and rivers. Despite the importance of freshwater ice, there has been a recent reduction in observational recordings.

The southern mountainous taiga region of eastern Siberia is the runoff source area of the basins of the rivers Lena and Amur, where snowmelt discharge is an important hydrological process. To evaluate the effect of the sparse larch forest canopy on snow ablation and energy balance in the snowpack, meteorological conditions and snow ablation were observed in a larch forest (LF) and an open field (OP). At the beginning of snowmelt, the snow water equivalent was 54.4 and 95.5 mm at OP and LF, respectively. The snow disappeared at LF three days later than at OP. Sublimation accounted for about 8% of snow ablation at both sites from 1 April to 5 May 2002, the snowmelt period. The energy balance of the snowpack at the two sites was dominated by the net all-wave radiation onto the snow surface. The difference in snowmelt between the sites was primarily caused by a difference in the net all-wave radiation. Snow surface albedo correlated with snow surface density for densities from 150 to 350 kg m -3 at both sites. Ablation de la neige à découvert et sous mélézin dans la région montagneuse sud de la Sibérie orientaleRésumé La région de taïga montagneuse méridionale de la Sibérie orientale est la zone d'origine des écoulements des bassins des Fleuves Lena et Amour, zone dans laquelle le débit de fonte des neiges est un processus hydrologique important. Pour évaluer les effets du maigre couvert de mélèze sur l'ablation de la neige et sur le bilan énergétique dans le couvert neigeux, les conditions météorologiques et l'ablation de la neige ont été observées dans une forêt de mélèzes (FM) et hors forêt (HF). Au début de la fonte des neiges, l'équivalent en eau était respectivement de 54.4 et 95.5 mm en HF et FM. La neige a disparu en FM trois jours plus tard qu'en HF. Entre le 1er avril et le 5 mai 2002, période de la fonte des neiges, la sublimation a représenté environ 8% de l'ablation de la neige. Le bilan énergétique du couvert neigeux a été dominé, dans les deux sites, par le rayonnement net total à la surface de la neige. La différence de fonte entre les sites a été principalement causée par une différence de rayonnement net total. L'albédo de la surface de la neige a été corrélé avec la densité de la surface de la neige, pour des densités variant entre 150 et 350 kg m -3 , pour les deux sites.

This article is concerned with assessment of changes in two critical characteristics of lake and river ice regime, namely ice cover duration and maximum ice thickness, in the period from the beginning of the 80s to the present, which is characterized by higher temperatures in the Northern Hemisphere compared with the previous period. The above ice regime characteristics are often limiting factors in winter operation of lakes and rivers (navigation, hydraulic construction works in cold period, construction of ice roads etc.). Assessment of changes in ice characteristics of lakes and rivers has been made for 52 river and five lake gauging sites of the Asian part of Russia (APR) using long-term observation data from the Russian observing network. Long-term series of the above characteristics were divided into two periods: from 1955 to 1979 (the period of stationary climate) and from 1980 to 2014 (non-stationary climate) and assessed from the point of view of their homogeneity and trend significance by Student's t-test. The research has found that at most of the sites in the APR, both ice cover duration and maximum ice thickness decreased during non-stationary climate period compared with the previous one. The greatest quantitative changes have occurred in the Eastern Siberia (average net decrease in ice cover duration amounted to 7 days•decade −1 and in maximum ice thickness-20 cm•decade −1 ) and in the Amur River basin (7 days•decade −1 and 17 cm•decade −1 respectively).