Future of Frozen Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 274

Fig. 9.4 Travelling on ice is always risky. To prepare for crossing by foot, skiing or skating, it is
good to take a sharp stick to test ice and ice picks to get up after ice breakage, also rope to help
others. Photograph by Finnish Swimming and Lifesaving Federation, printed with permission

with ice thickness squared so that for a skier or skater 5 cm is enough. When the thickness
of the ice is very close to the limiting minimum, special care must be taken because of the
natural variability of ice thickness and the resonance effects with shallow water waves for
moving loads (Fig. 9.4 ).

9.3 What Will Be?

Lakes are normally frozen at latitudes higher than 40 and at high altitudes in winter.

In these northern and southern caps there are open water lakes due to geothermal heat,
great depth or high salinity. Perennial lake ice is rare and found only in speci

- 50 °

c high polar
and high altitude environments. The annual course of the thermal structure of lakes is
forced by local climatology, and the boundaries of lake ice zones consequently vary along
the climate variations. The low latitude limit is the 0

° C isothermal where very shallow

lakes still may freeze over.
The physics of ice-covered lakes is presently rather well understood (Kirillin et al.
2012). The main questions are connected to the melting of ice and to the mechanical
displacements and drift of the ice cover. New-level, coupled ice liquid water body models

are needed to improve our understanding of ice season processes and phenomena. The
coupling takes place via the solar radiation and heat loss from the lake to the atmosphere,
which both depend on the thickness of the ice. Two- and three-dimensional modelling of
ice-covered lakes is required more with appropriate process-based links to the seasonal
dynamics of the lakes.
The climate change question focuses for the physics on the ice phenology and maxi-
mum annual ice thickness. In large lakes, ice concentration is as well examined. The
expected changes can be qualitative as seasonally freezing lakes may change into occa-
sionally freezing lakes, and ice may disappear from sites at the climatological ice margin.

-