Specific features of formation ans dynamics of ice events and ice thickness on the rivers of the Lena river basin
Vuglinsky Valery (1)
(1) Hydrologist
Specific features of formation and dynamics of ice events and ice cover thickness on the rivers of the Lena river basin
Valery Vuglinsky, State Hydrological Institute, 2nd Line 23, 199053, St.Petersburg, Russian Federation
Abstract
The Lena river basin occupies 2.5 mln sq.km in East Siberia and it is extended within several geobotanic zones, i.e. tundra, forest tundra, plain taiga and mountain taiga. Great variations in climate and orography in this territory cause a great space variety in the type of ice events formation and in basic ice cover characteristics. In the southern part of the Lena river basin (southern mountain taiga zone) the beginning of ice events formation in small and mid-size streams occurs 1 to 10 October and the end of these events occurs during 10-15 May; the duration of the period with all types of ice events varies within 220-230 days. In the northern part of the Lena basin (tundra zone) ice events in small and mid-size streams are observed 10 to 15 days earlier and they are over 10 to 15 days later; the duration of the period with different ice events lasts up to 240-250 days. Similar great differences are observed in the maximum ice cover thickness which is 50-70 cm on the rivers in the south and up to 150-200 cm on the streams in the arctic tundra.
Specific features in the dynamics of ice events and ice cover thickness have been considered for 15 streams as a case studies, different in size and flowing in different parts of the Lena river basin. For this purpose, long term data on the dates of beginning and ending of ice events and on the maximum ice cover thickness have been collected and analysed. Observation series on the dates of ice events were 30 to 45 years long; observation series on ice cover thickness were 15 to 25 years long. The analyses of the above data shows that on all the study rivers and streams later dates of ice events formation and earlier dates of ice events ending are observed, thus making the period with ice events 5 to 8-10 days shorter. The least significant decrease of the period with ice events occurred at hydrometric sites in the lower reaches of the Lena river. Ice cover thickness on all the study streams has been reduced by 10-50 cm; the maximum decrease in the ice cover thickness happened in the streams in the northern part of the Lena basin. For example, the maximum ice cover thickness at Kiusiur has been reduced from 210 cm to 140 cm during 1978-2000.
A joint analyses of long-term changes in the characteristics of ice regimes and mean winter air temperature has been made for some hydrometric sites; the analysis shown a close correlation between these variables. A positive trend towards rise in winter air temperature is accompanied by a shorter duration of ice events on the rivers.
The results of the studies are considered; objectives for the future work in this field are formulated.