Better understanding of permafrost in Lena and Yenisei river basins

Abstract

Permafrost covers over 60% of the territory in the central Siberia region. In recent years, there has been growing evidence to suggest that the runoff in central Siberia has shown an increase. This is suspected to be associated with the permafrost thawing in central Siberia. In the Arctic, terrestrial water storage plays a vital role in the annual water budget. The thawing of permafrost would compensate for groundwater in central Siberia, thus affecting local groundwater storage. In this study, an investigation was conducted into the variations in terrestrial water storage and runoff across the Yenisei and Lena basins located in central Siberia, for analyzing the variation of local permafrost during the period from 2003 to 2011. Over the past 40 years, the number of GRDC in-situ runoff observation stations has been reduced on a continued basis by as much as about 75%. Thus, the estimated runoff values were attempted as a replacement for the in-situ observed runoff values. Based on the hydrometeorological approach, the estimated runoff values were obtained by using the terrestrial water storage data collected from GRACE mascon solutions and the vertically integrated moisture flux divergence data sourced from ERA-Interim reanalysis model. The terrestrial water storage measured by GRACE represented a significant positive linear trend in both basins from 2003 to 2011. During this period, the annually measured runoff from GRDC also showed a moderate linear increasing trend in the Yenisei basin and a weak linear increasing trend in the Lena basin. The annually estimated runoff demonstrated a slightly positive linear trend in Yenisei basin but a weak negative trend in Lena basin. Moreover, a comparison was performed between the estimated runoff values and the in-situ observed runoff values to assess the performance of the estimated runoff. The validation indicates that the estimations would underestimate the runoff and have a considerable fluctuation and dispersion degree. Finally, we discussed the impact of changes in terrestrial water storage and runoff on changes in permafrost with the assistance of the permafrost map provided by the International Permafrost Association (IPA). Base on the characteristics of permafrost, we speculated that the changes of terrestrial water storage and runoff during the period from 2003 to 2011 might be attributed to the thawing of continuous permafrost and growth of new talik or expansion of existing talik within the discontinuous permafrost in the central Siberian region.