Ice forms on lakes and rivers due to seasons cooling during winter. The terrestrial Arctic hydrological cycle is divided into four periods, snowmelt, outflow breakup, summer ice-free, and winter. Outflow breakup is when 75% of annual water flow occurs over several days. Summer ice-free is when evaporation is significant. Winter is when thick ice exists over major rivers and lakes. Unlike the oceans, lakes and rivers normally only have local effects on climate. Annual ice breakup is related to average temperatures and air masses during the spring melt season. Annual freeze up of lakes often varies, depending on average temperatures and the prevailing air masses during the autumn freeze up season. In particular, individual lake freeze up is controlled by the heat content of the lake, which is strongly linked to water depth. As a result, deep lakes typically freeze up later than shallow lakes. Although, the freeze up and break up dates of individual lakes may not have a strong correlation to regional climate, a regional compilation of multi-year lake freeze and breakup data, may strongly correlate to regional climate. This can be a useful measure for regional climate change, where weather stations are not closely spaced. Northern river freeze up strongly correlates with the flow regime of a river rather than any climatic parameter. What do you think drives water flow within a river? A) Precipitation, B) Groundwater flow into the river, C) Snow melt, and/or D) Oceanic tides. More than one answer may be correct, so check all that you think apply. Answers A, B, and C are correct. Water flow within a river is typically driven by precipitation, groundwater flow into the river, snow melt, as well as the proportion of water running off the surface of the land. Ocean tides would not effect more than the mouth of a river. Northern rivers can be subdivided into four types. The Arctic nival is where ground water infiltration is minimal due to the perennially frozen ground. This leads to low winter flow and snowmelt being the major annual flow event. The Subarctic nival is dominated by spring snowmelt, but often enhanced by ice jam flooding with some ground water inflow. Proglacial is when snowmelt is still a significant event, but high flow is maintained throughout the summer due to higher elevation and glacial melting. Finally, muskeg is where low relief and poor stream connectivity lead to a lessening of the importance of snowmelt due to intervening water storage. Due to their kinetic energy and mixing, Arctic nival, Subarctic nival, and proglacial rivers tend to take longer to freeze for a given air temperature. However, human influences such as the presence of dams and diversion features, can affect freeze up. In a warming world with increased carbon dioxide, do you think ice jam floods would become more common or less common? A) Less common because warmer air temperatures would promote earlier melt. B) More common because the high flow favorable to ice jam flooding Would arrive earlier in the season. C) More common because warming would happen earlier in the season when river ice has not yet thinned. D) Less common, because river ice would still be thick early in the season. More than one answer might be correct, so check all that you think apply. Answers B and C are correct. Under conditions of increased carbon dioxide, ice jam floods may become more common along many northern rivers. With the increased likelihood of unseasonably warm weather events in the upper reaches of northern rivers, the high flow conditions most favorable to ice jam flooding are likely to arrive earlier in the melt season, when more northerly river ice has not yet thinned. Flow regime is a strong contributor to the spring breakup of northern rivers. But there is also a strong correlation to melt water production from the snow pack within the drainage basin. Many northern rivers flow northward to the Arctic Ocean, across a range of latitudes. Where spring temperatures increase melt water availability in more southern regions, the increased water flow often leads to breakup of river ice due to rising river levels. This often creates ice jams or ice dams along the more northern regions of these rivers, immense accumulations of fragmented ice that decreases or even blocks flow. Ice jams tend to occur at narrow points in a river channel, river confluences, and at obstacles in a channel, such as bridge piers. They are significant problem for northern communities and infrastructure along such rivers. These blockages can create dangerously rapid flooding upstream from the ice dam. When ice dams breach, they can also cause extensive flooding downstream, carrying masses of broken ice, scouring the river bed, and damaging river bank ecosystems. Northern jurisdictions often invest substantial funds in mitigating against ice jam floods. They will induce break up by applying low albedo dark sand to the ice to speed up melting, using ice-breaking ships, or even drilling holes in the river ice. Sometimes ice jams are removed by using explosives. [LAUGH] The effectiveness of such measures is highly variable. And at times have done nothing to mitigate damaging ice jam floods.
