River‐ice hydrology in a shrinking cryosphere

Abstract

Abstract:Many rivers of cold, and even temperate, regions of the globe are covered with ice for a part of the year. Projections of future climate indicate that the duration, composition and extent of ice coverage, however, will gradually change. This may have wide-ranging consequences because ice is a critical component of cold-regions hydrologic systems and strongly affects, for example, extreme floods, low winter flows, river transport, hydroelectric production, and numerous ecological and waterquality characteristics. Following an overview of the processes characterizing the freezeup-ice growth-breakup sequence, the links of river ice to the hydrology of northern rivers are examined in detail. The rise in river stage that is caused by an ice cover is shown to be fundamental to ice-related hydrologic impacts, such as floods caused by freezeup and breakup ice jams, low winter flows caused by water storage during freezeup and sharp waves generated by ice-jam releases. Ice thickness and strength, both controlled by weather conditions, also play major roles. To date, the sensitivity of river-ice regimes to changes in climatic conditions has only been partly evaluated. Most studies have focussed on ice phenology and indicate trends that are consistent with changes in air temperature, while a few recent studies have addressed the more complex questions of how climate change may alter ice thickness or the severity of extreme ice jams and floods. Foreseeable changes to river-ice regimes, and associated hydrologic processes and impacts, are discussed in the light of current understanding. More frequent occurrence of mid-winter breakup and associated jamming is a major effect that can be predicted with some confidence for regions where such events are presently rare or unknown. It is stressed that gaps in current knowledge preclude quantitative prediction of site-specific changes to river-ice regimes, and several recommendations for future research are presented.

Winter Disturbances and Riverine Fish in Temperate and Cold Regions

“…In contrast, a thick ice cover that adheres to the streambed and banks can result in substantial geomorphic disruption during floods (Cunjak et al 1998). Breakup floods can carry sediment loads two to five times higher than those observed under equivalent open-water floods (Beltaos and Prowse 2009). Ice jams and subsequent surges can divert the floodwater onto the floodplain (Brown RS et al 2001), causing channel shifts and major erosion over many kilometers, and are able to transport boulders up to 2 m in diameter (Doyle et al 1994).…”

“…Precipitation will more frequently fall as rain instead of as snow, leading to higher winter discharges, lower spring flood peaks, and more rain-on-snow events (Kundzewicz et al 2007). The ice regime will become more dynamic because of more frequent shifts between freezing and thawing (Beltaos and Prowse 2009). …”

Monitoring ice break-up on the Mackenzie River using MODIS data

“…Air temperature plays an important role on the timing of spring freshet (Beltaos and Prowse, 2009;Goulding et al, 2009b;Prowse and Beltaos, 2002) in the MRB. It has therefore been associated with increased flow and the initiation of ice break-up in the basin as a result of snowmelt onset (Abdul Aziz and Burn, 2006).…”

“…River-ice break-up on the Mackenzie River (MR) is a process by which upstream (lower latitude) ice is pushed downstream while intact ice resists movement downstream (higher latitude) (Beltaos and Prowse, 2009). Ice break-up is defined as a process with specific dates identifying key events in space and time between the onset of melt and the complete disappearance of ice in the river.…”

Quantitative historical hydrology in Europe

“…Other factors enhancing flood severity through time include timing of melting of glaciers (Debret et al, 2010). Global warming is introducing changes in the spatial (latitudinal) and temporal (seasonal) distribution of flooding related to ice and snowmelt (Beltaos and Prowse, 2009). For example, changes in the hydrometerological conditions that generate flooding may enhance flood magnitude in Norway, due to an earlier onset of snowmelt related to flooding in the region (Hisdal et al, 2006), whereas in mainland Europe, flooding related to ice jams is now unlikely to occur .…”