JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D18102, doi:10.1029/2004JD004583, 2004 Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change J. W. McClelland, R. M. Holmes, and B. J. Peterson The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA M. Stieglitz Department of Civil and Environmental Engineering and School of Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA Received 29 January 2004; revised 21 May 2004; accepted 8 June 2004; published 17 September 2004. [1] 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. INDEX TERMS: 1655 Global Change: Water cycles (1836); 1803 Hydrology: Anthropogenic effects; 1833 Hydrology: Hydroclimatology; 1860 Hydrology: Runoff and streamflow; KEYWORDS: Arctic river discharge, global change Citation: McClelland, J. W., R. M. Holmes, B. J. Peterson, and M. Stieglitz (2004), Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change, J. Geophys. Res., 109, D18102, doi:10.1029/2004JD004583. 1. Introduction and global climate involve the hydrologic cycle. For exam- ple, changes in the moisture content of Arctic soils influence [2] The Arctic is a central component of the global uptake and release of greenhouse gases [Gorham, 1991; climate system. Increasing temperatures in recent decades McKane et al., 1997; Oechel et al., 1993; Stieglitz et al., have been linked to a wide variety of changes in the Arctic 2000], and changes in freshwater inputs to the Arctic Ocean [Serreze et al., 2000]. At the same time, changes in have the potential to alter global ocean circulation the Arctic may have strong feedbacks on global climate [Broecker, 1997; Manabe and Stouffer, 1994; Rahmstorf, [Intergovernmental Panel on Climate Change (IPCC), 2002]. This second feedback recently became the focus of 2001]. Many of the linkages between the Arctic system heightened attention after publication of records showing long-term increases in river discharge from Eurasia into the Copyright 2004 by the American Geophysical Union. Arctic Ocean [Peterson et al., 2002]. Discharge to the 0148-0227/04/2004JD004583 Arctic Ocean from the six largest Eurasian rivers D18102 1of12 D18102 MCCLELLAND ET AL.: INCREASING RIVER DISCHARGE IN THE ARCTIC D18102 work against any long-term increase in discharge. Similarly, controlling the seasonality of flow could have a positive or negative influence on long-term trends in annual discharge. Evaporation from reservoirs decreases discharge. However, increasing the proportion of water flowing to the Arctic Ocean during times of year when evaporative demand is low could result in higher annual values. [5] Permafrost thaw is another obvious subject of enquiry because water stored in permafrost could become runoff after melting. While permafrost depths can reach several hundred meters, the upper 20 m of permafrost alone in the Northern Hemisphere contains 11,000–37,000 km3 of fro- zen water, much of which is in the Eurasian Arctic [Zhang et al., 1999, 2000]. These volumes of water are much larger than the excess 4160 km3 of river water delivered to the Arctic Ocean between 1936 and 1999 [Peterson et al., 2002]. Thus water stored in Eurasian Arctic permafrost has the potential to make major contributions to Arctic river discharge. [6] Forest fires have been suggested as a potential mech- anism behind the long-term changes in Eurasian Arctic river discharge because changes in vegetation following fires Figure 1. Watersheds and average annual discharge from often lead to greater runoff. Loss or damage of vegetation the six largest Eurasian Arctic rivers. Boundary of the pan- causes a decrease in evapotranspiration, allowing a greater Arctic watershed (red line) is shown. proportion of precipitation to become runoff [Chapin et al., 2000]. This effect diminishes over time as the forest 6 (Figure 1) increased by 128 km3 yÀ1 from 1936 to 1999. recovers. There are 620 Â 10 ha of boreal forest in Russia This change in discharge was correlated with global [Conard and Ivanova, 1997]. The vast majority of this surface air temperature. Furthermore, calculations of forest lies within the combined watershed of the six largest future discharge coupled to Intergovernmental Panel on Eurasian Arctic rivers. Thus, as with permafrost thaw, Climate Change global warming scenarios suggested that increased fires in Russia’s boreal forests have the potential additional freshwater contributions to the Arctic Ocean to substantially alter river discharge. could significantly impact North Atlantic Deep Water [7] In this paper we consider the influence of dams, formation within this century [Peterson et al., 2002]. permafrost thaw, and fires with respect to the observed [3] Accurate projections of Arctic river discharge depend long-term changes in discharge from the six largest Eurasian on identifying the specific mechanisms driving the changes. Arctic rivers. Comprehensive long-term records of river The projections of Peterson et al. [2002] assume increased discharge made it possible to evaluate the role of dams net atmospheric moisture transport from lower to higher directly. Data on permafrost thaw and fires in the water- latitudes in a warming climate as indicated by many global sheds of the Eurasian Arctic rivers are less useful because circulation models [IPCC,2001;Manabe and Stouffer, temporal and spatial coverage is limited. We therefore use a 1994; Rahmstorf and Ganopolski, 1999]. Yet uncertainty combination of data and modeling scenarios to explore the associated with estimates of precipitation in the Eurasian potential of these two mechanisms as drivers of increasing Arctic makes it difficult to confirm whether or not this Arctic river discharge. mechanism was responsible for the changes in river dis- charge observed thus far [Serreze et al., 2003; Serreze and Etringer, 2003; Yang et al., 2001]. Three alternative mech- 2. Data Sets and Methods of Analysis anisms that have been suggested frequently to account for 2.1. Dams the long-term changes in river discharge are dam construc- [8] The Russian Federal Service of Hydrometeorology tion and operation, permafrost thaw, and increasing forest and Environment Monitoring (Roshydromet) has been mea- fires. suring river discharge at many stations within the Russian [4] Numerous large dams have been built in Russia and Arctic for much of the past century [Lammers et al., 2001; the former Soviet Union, including several in the water- Peterson et al., 2002; Shiklomanov et al., 2002]. Errors sheds of the major Eurasian Arctic rivers (L. K. Malik et al., associated with the discharge estimates vary seasonally, Development of dams in the Russian Federation and NIS with greatest uncertainty during the ice breakup period. countries, 2000, at http://www.dams.org/kbase/studies/ru/). However, estimates of discharge become increasingly well The influence of these dams on long-term discharge trends constrained from daily to monthly to annual averages. For could be important, as dams have a major influence on example, on the Ob’ River at Salekhard, errors in daily watershed storage and flow regimes [Vo¨ro¨smarty et al., discharge estimates range from 26% in April to 5% in July, 1997]. All else being equal, filling of reservoirs near the errors in monthly discharge estimates range from 18% in beginning of a record would make discharge values lower April to 3% in July, and the error in annual discharge