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1. Introduction
Annual average temperatures over the Arctic have increased at nearly twice the rate observed for the rest of the globe over the last few decades (ACIA 2005), and paleoclimate records indicate that recent temperatures in the Arctic are the highest they have been in the last 400 yr (Overpeck et al. 1997). Scientists and indigenous peoples have observed many changes in the Arctic, indicating that the region is undergoing a system-wide response to a changing climate (Hinzman et al. 2005). Research interest in Arctic regions derives partly from the region’s sensitivity to global change, and partly from the fact that climate-induced changes in the Arctic have the potential to feed back to the global climate system; for example, increasing freshwater flux to the Arctic Ocean may cause a weakening of the World Ocean’s thermohaline circulation (THC) by inhibiting deep-water formation in the North Atlantic (Broecker 1997; Clark et al. 2002; Curry et al. 2003). Implications of THC changes include slowing the rate of warming (and perhaps even cooling) over the North Atlantic and northern Europe, and slowing of CO2 transport to the deep ocean, leading to increased global warming (ACIA 2005).
Combined annual streamflow volumes from the six largest Eurasian basins increased by approximately 7% (or 2.0 ± 0.4 km3 yr−1) between 1936 and 1999 (Peterson et al. 2002; Shiklomanov et al. 2006). Changes in annual runoff have been accompanied by shifts in seasonality. In general, the largest increases have been observed during the cold season, which is also the season of low flow (October–April), while the spring snowmelt peak has shifted earlier (Georgievskii et al. 1996; Yang et al. 2004a, b; Yang et al. 2002), although this is not the case for all rivers. Changes in other seasons are generally less robust; for the Lena and Ob’ River basins, summer discharges have slightly increased, whereas fall discharges have slightly decreased (Yang et al. 2004b; Yang et al. 2002; Ye et al. 2003).
Notwithstanding the potential for observed Arctic river discharge changes to affect global climate, there is little current understanding of the primary controls on Arctic river streamflow change and variability, as evidenced by conflicting explanations for observed historical changes. Knowledge of these controls would arguably facilitate better...