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Future Predictions for Lake Ice
A variety of approaches can be taken to develop scenarios of how lake ice conditions may look under future climatic states. Empirical sceanrios can be developed based on the observed sensitivity of lake ice to controlling variables, or physical models of lake ice can be applied to simulate ice cover under future climatic states. To date, most Global Climate Models lack the spatial resolution to resolve lakes, so it is not possible to present results directly from GCM output.
Empirical Scenarios for Canadian Lakes
Numerous studies have been carried out to document the observed sensitivity of freeze-up and break-up to meteorological parameters such as air temperature, snowfall, wind speed, and cloud cover, and non-climatic parameters such as latitude, and lake size. A comprehensive review of literature pertaining to Canadian lakes is provided by Skinner (1986, 1993). Air temperature is the most important variable controlling freeze-up and break-up, and Skinner (1993) presented simple temperature regression relationships for 8 regions of Canada that typically were able to explain more than 60% of the observed variance. Skinner found that a 1°C change in air temperature in any region resulted in a ~2 to 3 day change in freeze-up and break-up. Global Climate Model scenarios indicate a fall and spring season warming of ~2 to 4°C over much of North America by 2050. From the observed lake ice temperature sensitivity, this translates into a reduction in lake ice cover over Canada in the order of 12-24 days by the middle of this century.
Model Sensitivity Results
An advantage of physical models of the ice formation process is that these allow detailed investigations to be carried out of how an ice cover may respond to a changing climate. For example, Figure 1 shows the sensitivity of open water duration simulated by the 1-D Flato (1995) thermodynamic ice growth model, to the timing of a temperature change. The results clearly show a maximum temperature sensitivity in the spring period (break-up), and a smaller peak in the fall (freeze-up). Similar results for snowfall sensitivity are shown in Figure 2 which shows that increasing snowfall has contrasting effects on open water duration, depending on the time of year (additional snow in spring delays break-up, additional snow in the fall delays complete freeze over).
Physical models can be used to construct a multi-variate response surface to investigate the implications of different climates on ice cover conditions. For example, the following table presents open water duration as a function of a range of temperature and snowfall conditions, and allows the construction of a number of different scenarios e.g. the table shows a change from the current climate regime (blue/violet) to one associated with an increase in mean annual air temperature by 3°C, and an increase in snowfall by 50% (violet/red).
| Snowfall Rate mm/day ® |
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
| -2°C |
* |
* |
* |
31 |
26 |
* |
* |
* |
* |
| -1°C |
* |
35 |
50 |
56 |
56 |
53 |
47 |
41 |
32 |
| 0°C |
40 |
60 |
70 |
73 |
74 |
71 |
69 |
66 |
62 |
| +1°C |
65 |
76 |
82 |
87 |
87 |
85 |
84 |
81 |
78 |
| +2°C |
82 |
90 |
94 |
97 |
97 |
97 |
95 |
93 |
91 |
| +3°C |
94 |
101 |
105 |
107 |
107 |
106 |
105 |
103 |
102 |
| +4°C |
105 |
109 |
113 |
115 |
116 |
115 |
113 |
112 |
111 |
| +5°C |
115 |
119 |
122 |
124 |
124 |
124 |
123 |
122 |
119 |
| +6°C |
124 |
127 |
130 |
132 |
133 |
132 |
131 |
130 |
128 |
| * No Breakup |
Table 1: Modelled sensitivity of open water duration (days) to changes in mean annual air temperature and snowfall rate for a seasonal ice regime in the Canadian high Arctic. Based on 1955-1990 mean climate data from Resolute (74.7ºN, 95.0ºW). The observed range in climate conditions over the 1955-1990 period is shown in blue/violet (mean = 70 days). The numbers in violet/red show the new open water regime (mean = 107 days) for a scenario with 3 degree warming and a 50% increase in snowfall. A description of the ice model is provided in Flato and Brown (1996).
References
- Flato, G.M. and R.D. Brown. 1996. Variability and climate sensitivity of landfast Arctic sea ice. J. Geophys. Res., 101(C10): 25,767-25,777.
- Skinner, W.R., 1986: The break-up and freeze-up of lake and sea ice in northern Canada. Canadian Climate Centre Report 86-8, Atmospheric Environment Service, Downsview, Ontario, 62 pp.
- Skinner, W.R., 1993: Lake ice conditions as a cryospheric indicator for detecting climate variability in Canada. Proc. "Snow Watch '92," R. G. Barry, B. E. Goodison, and E. F. LeDrew (eds.), World Data Center A for Glaciology, Glaciological Data Report GD-25, 204-240.
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