Cooperative Institute for Research in Environmental Sciences

Abstracts: 12

Large-scale Hydro-climatology of the Terrestrial Arctic Drainage System

Mark C. Serreze¹, David H. Bromwich², Martyn P. Clark¹, Andrew J. Etringer¹, Tingjun Zhang¹ and Richard Lammers³

¹ Cooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder CO
² Byrd Polar Research Center, The Ohio State University, Columbus OH
³ Water Systems Analysis Group, University of New Hampshire, Durham NH

The large-scale hydro-climatology of the terrestrial Arctic drainage system is examined, focusing on the period 1960 and onward. Special attention is paid to the Ob, Yenisey, Lena and Mackenzie watersheds, which provide the bulk of freshwater discharge to the Arctic Ocean. Station data are used to compile monthly gridded time series of gauge-corrected precipitation (P). Gridded time series of precipitation minus evapotranspiration (P-ET) are calculated from the moisture flux convergence using NCEP reanalysis data. Estimates of ET are obtained as a residual. Runoff (R) is obtained from available discharge records.

For long-term water-year means, P-ET for the Yenisey, Lena and Mackenzie is 16-20% lower than observed runoff. In the Ob the two values agree within 9%. Given the uncertainties in P-ET, we consider the atmospheric and surface water budgets to be reasonably well closed. Compared to the other three basins, the mean runoff ratio (R/P) is lower in the Ob, consistent with the high fraction of annual precipitation lost through ET. All basins exhibit summer maxima in P and minima in P-ET. Summer P-ET in the Ob is negative due to high ET rates. For large domains in northern Eurasia, about 25% of July precipitation is associated with recycling of water vapor evapotranspirated within each domain. This points to a significant effect of the land surface on the hydrologic regime.

Variability in P and P-ET has generally clear associations with the regional atmospheric circulation. A strong link with the Urals trough is documented for the Ob. Relationships with indices of the Arctic Oscillation and other teleconnections are generally weak. Water year time series of runoff and P-ET are strongly correlated in the Lena only, reflecting extensive permafrost. Cold-season runoff has increased in the Yenisey and Lena. This is most pronounced in the Yenisey, where runoff has also increased sharply in spring, decreased in summer, but has increased for the year as a whole. The mechanisms for these changes are not entirely clear. While they fundamentally relate to higher air temperatures, increased winter precipitation, and strong summer drying, we speculate links with changes in active layer thickness and thawing permafrost.