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This project is funded by NSF
To document several elements, including permafrost and ground ice distribution; changes in permafrost temperature, active layer thickness, and length of thaw season over the past few decades; and their impact on the hydrologic cycle over three Siberian river basins (the Ob, Yenisey, and Lena)
Tingjun Zhang is the PI and Roger G. Barry is Co-Investigator.
Recent studies indicate that runoff over the Siberian Arctic drainage basins has increased substantially over the past several decades. The source of water causing the runoff increase is unknown. In this study, we hypothesize that changes in the active layer and permafrost dynamics play a role in the recent changes in the Arctic hydrological regime.
Permafrost underlies approximately 4 to 10 percent of the total area of the Ob basin, 36 to 55 percent in the Yenisey basin, and 78 to 93 percent in the Lena basin. Consequently, total volume of the excess ground ice varies from approximately 302 to 854 cubic kilometers in the Ob, 1,699 to 2,462 cubic kilometers in the Yenisey, and 3,523 to 4,227 cubic kilometers in the Lena basin. According to ground-based measurements, mean annual soil temperature at the 40-centimeter depth has increased about 1.3 degrees Celsius in the Ob, 0.8 degrees Celsius in the Yenisey, and 1.6 degrees Celsius in the Lena river basin for the period from 1930 through 1990. The increase is more pronounced from the mid 1960s to 1990. An increase in the near-surface soil temperature leads to lateral thawing of permafrost and thickening of the active layer. Long-term soil temperature measurements indicate that permafrost has been degrading during the past several decades. Active layer thickness has increased about 30 centimeters from the mid 1950s to 1990s over the Lena river basin. Thawing index has increased substantially over all three river basins from the 1950s to 1990s, implying that the increase in active layer thickness is a widespread phenomenon over the Russian Arctic drainage basin during the past few decades.
Changes in active layer thickness of 15 centimeters produce a runoff equivalent of about 0.9 to 2.4 millimeters in the Ob, about 7.8 to 11.3 millimeters in the Yenisey, and about 15.3 to 19.4 millimeters in the Lena. An anti-correlation of changes in active layer thickness and runoff may exist due to possibly high evaporation and storage in the thickened active layer. There might be a time lag between changes in active layer thickness and runoff. Late freeze-up of the active layer may also contribute to the increase in the winter runoff. Overall, changes in permafrost conditions in the Ob basin have a minimum impact on runoff. Lateral thawing of permafrost and thickening of the active layer may account for the significant increase in runoff over the Yenisey river basin. Melting of the excess ground ice through thickening of the active layer might be one of the major sources of runoff in the Lena river basin. Further work will include better understanding of the rate of lateral thawing and spatial permafrost distribution of discontinuous, sporadic, and isolated permafrost.
Digitized versions of permafrost maps are available from the NSIDC Frozen Ground Data Center Web site.
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