科研之友
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摘要
Although river ice is a major component of the cryosphere and is particularly important to many river processes, including extreme events, its full geographical coverage has never been documented. Recognizing that the freeze-up and break-up of river ice is closely linked to the timing of 0 degrees C air temperatures, this study analyses the spatial extent of river networks relative to the location of three 0 degrees C isotherm periods. These were defined to represent a suite of ice-affected conditions that would be experienced for 6, 3 or 0.5 month periods, the briefest interval possibly leading only to a very thin and transient ice cover or simply border/frazil ice formation. Four different GIS databases were used to represent the river networks. The percentages of the total Northern Hemisphere land mass (average river network) influenced by cold temperatures conducive to ice formation were 52, 45 and 25 (56, 47 and 28), respectively. The related southern position of the isotherms ranged from 33 degrees N, 35 degrees N and 50 degrees N in central North America to a nearly consistent 27 degrees N for Eurasia, reflecting the influence of the high-elevation central plateau region. Also identified are the lengths of major rivers that fall within the three 0 degrees C isotherm boundaries. Included are some of the world's largest rivers including the Lena, Mackenzie, Ob, Yellow, Yukon and Yenisey rivers, although their percentage of ice-affected coverage varied for the three isotherm periods from a consistent 100% for the Lena and Yukon rivers to as little as 23% at the 6-month interval for the Yellow River.
- 出版日期2010-1-15
