ANALYSIS OF INCREASED BASEFLOW ACROSS NORTHERN EURASIAN RIVERS UNDERLAIN BY PERMAFROST

The Arctic is currently warming at twice the rate of the global average, resulting in increased rates of Arctic river discharge and the thawing of perennially frozen ground known as permafrost. As permafrost thaws, the layer of soil above permafrost that thaws during the summer and refreezes in the winter known as the active layer, increases in depth. An increase in the depth of the active layer is postulated to be one of the main reasons why we have observed increased rates of river discharge in the Arctic. It is important to understand why and at what rate permafrost thaws, as the hydrology of permafrost is also intimately connected with the carbon cycle since thawing permafrost releases stored carbon as methane or carbon dioxide into the atmosphere more readily when soils are unsaturated, further accelerating climate warming. In this study we quantify how changes to Arctic permafrost relate to changes in Arctic river discharge by analyzing daily streamflow records across northern Eurasia for 139 different river discharge stations from 1913 to 2003. We perform a baseflow recession analysis for these stations for the low flow and snow-free months of September and October. We chose these low flow months when streamflow comes from groundwater storage or baseflow to minimize the influence of precipitation and snowmelt from higher elevations. Across all 139 river discharge stations we observe a positive recession flow intercept (a proxy for increasing active layer depth) for the majority of those stations underlain by continuous permafrost, while we see a negative recession flow intercept for stations underlain by less extensive permafrost including discontinuous, sporadic, isolated, and no permafrost regions. This may indicate that active layer is deepening in areas underlain by continuous permafrost which causes an increase in baseflow, while in areas without continuous permafrost, the increased baseflow may be caused by large scale permafrost thawing and an increase in regional hydraulic conductivity, or the ease at which water flows through the ground. The results from this work may help us to understand the changing hydrologic cycle in the Arctic which has implications for carbon cycling as the Arctic continues to warm.