Extreme events, trends, and variability in Northern Hemisphere lake-ice phenology (1855–2005)

Abstract

Often extreme events, more than changes in mean conditions, have the greatest impact on the environment and human well-being. Here we examine changes in the occurrence of extremes in the timing of the annual formation and disappearance of lake ice in the Northern Hemisphere. Both changes in the mean condition and in variability around the mean condition can alter the probability of extreme events. Using long-term ice phenology data covering two periods 1855-6 to 2004-5 and 1905-6 to 2004-5 for a total of 75 lakes, we examined patterns in long-term trends and variability in the context of understanding the occurrence of extreme events. We also examined patterns in trends for a 30-year subset (1975-6 to 2004-5) of the 100-year data set. Trends for ice variables in the recent 30-year period were steeper than those in the 100-and 150-year periods, and trends in the 150-year period were steeper than in the 100-year period. Ranges of rates of change (days per decade) among time periods based on linear regression were 0.3−1.6 later for freeze, 0.5−1.9 earlier for breakup, and 0.7−4.3 shorter for duration. Mostly, standard deviation did not change, or it decreased in the 150-year and 100-year periods. During the recent 50-year period, standard deviation calculated in 10-year windows increased for all ice measures. For the 150-year and 100-year periods changes in the mean ice dates rather than changes in variability most strongly influenced the significant increases in the frequency of extreme lake ice events associated with warmer conditions and decreases in the frequency of extreme events associated with cooler conditions.

Some Aspects of Ice-Hydropower Interaction in a Changing Climate

“…The changes in Fennoscandia averaged a decadal warming trend between 1961 and 2010 of 0.20 °C (autumn), 0.53 °C (winter) and 0.38 °C (spring) [15]. Concurrently, a number of other studies using historical observations of ice phenology (for lakes and rivers) have shown consistent evidence of later freezing and earlier breakup in the Northern Hemisphere [17][18][19]. Projections of future climate indicate that ice regimes (duration, extent and composition) will gradually change [15,20].…”

Environmental Impacts—Lake Ecosystems

“…Since the mid-19th century, there has been a general long-term decrease in the duration of ice cover in northern hemisphere lakes at a mean rate of about 1.2 days per decade , with the rate for individual lakes ranging from 0.9 to 1.7 days per decade (Benson et al 2012). This decline seems to be accelerating: over the last 30 years, the equivalent is 1.6-4.3 days per decade (Benson et al 2012).…”

“…Since the mid-19th century, there has been a general long-term decrease in the duration of ice cover in northern hemisphere lakes at a mean rate of about 1.2 days per decade , with the rate for individual lakes ranging from 0.9 to 1.7 days per decade (Benson et al 2012). This decline seems to be accelerating: over the last 30 years, the equivalent is 1.6-4.3 days per decade (Benson et al 2012). In regions with relatively brief or mild winters, where lakes are ice-covered for a comparatively short period-for instance in southern Sweden, Denmark and northern Germany-increasingly milder winters are likely to result in ice cover becoming intermittent or even disappearing Weyhenmeyer et al 2011).…”

“…It is likely that the phenology of ice cover on the lakes of the North Sea region will follow the global trend; with ice-on occurring later, ice-off occurring earlier, and a general reduction apparent in the duration of ice cover Benson et al 2012). However, several factors will modify this general trend.…”

Historical Trends, Drivers, and Future Projections of Ice Phenology in Small North Temperate Lakes in the Laurentian Great Lakes Region

“…Lake ice phenology (the timing of ice breakup, freeze up and duration) is highly sensitive to changes in climate [2,3] and therefore, long-term ice phenological records can serve as indicators of climate dynamics over time, both in the past and into the future. Over a 150-year period, ice has melted earlier, frozen later, and ice duration has become shorter in lakes and rivers across the Northern Hemisphere [2,4]. Specifically within the Great Lakes region, Jensen et al [5] found that on average, lake ice melted 6.3 days earlier (n = 64 lakes and 1 river) and froze 9.9 days later (n = 33 lakes) from 1975 to 2004.…”