Abstract
This study documents major changes in streamflow hydrology over the Kolyma watershed due to climatic variations and human impacts. Streamflow seasonal cycles over the basin are characteristic of the northern region, with the lowest runoff in April and peak flow in June. Analyses of monthly flows and trends show that reservoir construction and operation have considerably affected streamflow regimes. Comparisons of mean monthly discharge records between pre- and post-1986 dam periods indicate that the mid–lower basin (downstream of the dam) experienced significant increase in low flows and decrease in peak flows after dam construction. For example, mean monthly flows during the post-dam period at the Ust’-Srednekan station (located 1423 km downstream of the dam) has strongly increased by about 205 m3 s−1 (or 522%–3157%) during December–April, and decreased by 133 m3 s−1 (41%) in June. Long-term monthly discharge data reveal an overall increase in streamflow during low flow seasons; the increase is greater for the stations located downstream of the dam. The Srednekolunsk station (1720 km from dam) shows low flow increase ranging from 130 (43%) to 268 m3 s−1 (454%) during November–April, and high discharge decrease by 2550 to 519 m3 s−1 during June–August in the post-dam era (1986–2000). These changes in flow patterns are mainly caused by reservoir regulation, as reservoirs release water in winter for power generation and store water in summer for flood control. Dam impact on flow regimes and changes are visible along the main river trunk; thus, the cold season discharge increase at the basin outlet is primarily the result of reservoir regulation. Annual discharge records show different changes within the Kolyma basin, with moderate increases in the upper basin and weak decreases in the mid–lower basin. Overall annual discharge near the basin outlet has decreased by 1.5% during 1978–2000. This study emphasizes the importance of human activities (particularly reservoirs) on seasonal and regional hydrology changes and points to the need to further examine natural causes and human impacts over other high-latitude watersheds.
Corresponding author address: Ipshita Majhi, Water and Environment Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775. Email: ftipm@uaf.edu
