Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change

Abstract

Discharge from Eurasian rivers to the Arctic Ocean has increased significantly in recent decades, but the reason for this trend remains unclear. Increased net atmospheric moisture transport from lower to higher latitudes in a warming climate has been identified as one potential mechanism. However, uncertainty associated with estimates of precipitation in the Arctic makes it difficult to confirm whether or not this mechanism is responsible for the change in discharge. Three alternative mechanisms are dam construction and operation, permafrost thaw, and increasing forest fires. Here we evaluate the potential influence of these three mechanisms on changes in discharge from the six largest Eurasian Arctic rivers (Yenisey, Ob', Lena, Kolyma, Pechora, and Severnaya Dvina) between 1936 and 1999. Comprehensive discharge records made it possible to evaluate the influence of dams directly. Data on permafrost thaw and fires in the watersheds of the Eurasian Arctic rivers are more limited. We therefore use a combination of data and modeling scenarios to explore the potential of these two mechanisms as drivers of increasing discharge. Dams have dramatically altered the seasonality of discharge but are not responsible for increases in annual values. Both thawing of permafrost and increased fires may have contributed to changes in discharge, but neither can be considered a major driver. Cumulative thaw depths required to produce the observed increases in discharge are unreasonable: Even if all of the water from thawing permafrost were converted to discharge, a minimum of 4 m thawed evenly across the combined permafrost area of the six major Eurasian Arctic watersheds would have been required. Similarly, sensitivity analysis shows that the increases in fires that would have been necessary to drive the changes in discharge are unrealistic. Of the potential drivers considered here, increasing northward transport of moisture as a result of global warming remains the most viable explanation for the observed increases in Eurasian Arctic river discharge.

Relevance of Hydro-Climatic Change Projection and Monitoring for Assessment of Water Cycle Changes in the Arctic

“…This points to the importance of establishing the source of the growing river component in the Arctic Ocean freshwater budget. Increasing precipitation has been suggested as the main driver of increasing river runoff (Dyurgerov and Carter 2004;McClelland et al 2004). However, contradictory trends in discharge and precipitation have also been reported (Berezovskaya et al 2004;Milliman et al 2008).…”

“…Serreze et al (2002) however found only low correlation between P-E and runoff across the pan-Arctic drainage basin, except for the Lena basin. Several studies have discussed a possible contribution of melting permafrost to increased runoff (Serreze et al 2002;Adam and Lettenmaier 2008;Dyurgerov et al 2010), but at least for the Eurasian Arctic, the total volumes of melting permafrost that are needed to explain the long-term runoff increases seem unrealistic (McClelland et al 2004). …”

Streamflow hydrology in the boreal region under the influences of climate and human interference

“…The causes for these changes are unclear but the spring discharge increase has been attributed to an earlier snowmelt associated with warmer spring conditions, and changes in winter streamflow are perhaps associated with an increase in the depth of the active layer (seasonally frozen and thaw zone above the permafrost) under a warming climate (Yang et al 2002). McClelland et al (2004) suggested that increased precipitation was a key factor in streamflow augmentation, but not permafrost thaw or forest fire. Déry & Wood (2005) noted a flow reduction from northern continental Canada, including the Hudson Bay drainage.…”

Runoff characteristics of the Changjiang River during 2006: Effect of extreme drought and the impounding of the Three Gorges Dam

“…low runoff in drought years, floods during intense rainfall, and the warmed climate due to global warming effects [Intergovernmental Panel on Climate Change, 2001;Jiang and Shi, 2003;Romanovicz, 2007]. However, most researchers have focused on the flooding processes, occurrence mechanics and flood frequency in the river basin, along with regulation by dams and irrigation [McClelland et al, 2004;Berezovskaya et al, 2004;Onuchin et al, 2006]. Only a few studies have been conducted so far on the subject of riverine responses to the extreme drought events in drought years [Chen et al, 2001], especially to combined extreme drought event and underway impounding of the Three Gorges Dam (TGD).…”