Variation of hydrological regime with permafrost coverage over Lena Basin in Siberia

We use monthly discharge and permafrost data to examine the relationship between discharge characteristics and basin permafrost coverage for the nested subbasins of the Lena River in Siberia. There are similarity and variation in streamflow regimes over the basin. The ratios of monthly maximum/minimum flows directly reflect discharge regimes. The ratios increase with drainage area from the headwaters to downstream within the Lena basin. This pattern is different from the nonpermafrost watersheds, and it clearly reflects permafrost effect on regional hydrological regime. There is a significant positive relationship between the ratio and basin permafrost coverage. This relationship indicates that permafrost condition does not significantly affect streamflow regime over the low permafrost (less than 40%) regions, and it strongly affects discharge regime for regions with high permafrost (greater than 60%). Temperature and precipitation have similar patterns among the subbasins. Basin precipitation has little association with permafrost conditions and an indirect relation with river flow regimes. There exists a good relation between the freezing index and permafrost extent over the basin, indicating that cold climate leads to high coverage of permafrost. This relation relates basin thermal condition with permafrost distribution. The combination of the relations between temperature versus permafrost extent, and permafrost extent versus flow ratio links temperature, permafrost, and flow regime over the Lena basin. Over the Aldan subbasin, the maximum/minimum discharge ratios significantly decrease during 1942–1998 due to increase in base flow; this change is consistent in general with permafrost degradation over eastern Siberia.