ABSTRACT Since the 1930's, combined streamflow from the six largest Eurasian rivers discharging to the Arctic Ocean has been increasing. For many of these basins, an increase in annual streamflow volume is accompanied by a shift in seasonality. Potential causes of these changes include warming-induced agents of change (e.g. increasing precipitation, an earlier snowmelt, and permafrost degradation), as well as direct human effects, particularly that of the storage and release of river runoff in reservoirs. Large reservoirs in these river basins were constructed between 1950 and Currently operating large reservoirs (exceeding 1 km 3 in storage capacity) include one for the Lena, three for the Ob', and seven for the Yenisei (the Boguchany reservoir is still under construction). The purpose of this study is to provide an alternate method to estimate the climatic versus reservoir-induced effects on streamflow seasonality and annual streamflow volume, and to compare these estimates to those of prior studies. We simulate reservoir effects using a reservoir routing model coupled off-line to the Variable Infiltration Capacity (VIC) land surface hydrology model for the Lena, Yenisei and Ob' River basins. The simulation captures the main effects of reservoir operations, assuming that the primary purpose of each reservoir is to generate hydropower (i.e. reservoir releases are determined by maximizing hydropower revenue for each operational year). The potential of reservoirs to affect basin-average evaporation is also considered. We create a reconstructed streamflow product, for which the effects of the reservoirs are removed, by subtracting the simulated reservoir effects from observed streamflow at the outlets of each of the basins. We compare the reservoir signature of our product to those of two other reconstructed streamflow products that were derived only from observed streamflow data. Finally, we perform trend analysis on long-term (30+ years) time series of monthly, seasonal, and annual streamflow and separate out the effects of reservoirs. Study Domain Locations of operational dams for which the reservoir storage capacities exceed 1 km 3 (shown as solid red circles). The storage capacities of the reservoirs are given on a log ten scale by the diameters of the yellow circles; and the green crosses indicate the locations of the streamflow gauging stations used for reservoir model evaluation (see figure on right). Note: the Boguchanskoe dam on the Angara tributary to the Yenisei River is not shown because it is not yet operational. FINAL REMARKS Using a coupled hydrology-routing-reservoir model, we have simulated historical releases, storage, and reservoir evaporation for the major reservoirs in the Lena, Yenisei, and Ob’ River basins. Our simulations of the effects of reservoirs on streamflow seasonality at the basin outlets produce the same general features as reconstructed products that were derived purely from observed streamflow data (McClelland et al. 2004, Yang et al. 2004, and Ye et al. 2003). We have estimated the influence of reservoirs on long-term annual, seasonal, and monthly trends at the basin outlets. Although reservoirs have had little effect on annual trends, they are responsible for much of the seasonal changes that have been observed, especially during the winter. This is in agreement with other studies (McClelland et al. 2004, Yang et al. 2004, and Ye et al. 2003). Objective 1. Coupled Hydrologic/Reservoir/Routing Simulations Objective 2. Comparison of Reservoir Signatures to Those of Other Products Adam, J.C., F. Su, L.C. Bowling, and D.P. Lettenmaier, 2007, Application of a macroscale land surface model to a streamflow trend attribution study in Northern Eurasia, J. Clim. (in preparation). Haddeland, I., T. Skaugen, and D.P. Lettenmaier, 2006, Anthropogenic impacts on continental surface water fluxes, Geophys. Res. Lett., 33, L08406, doi: /2006GL Liang, X., D. P. Lettenmaier, E. F. Wood, and S. J. Burges, A Simple hydrologically Based Model of Land Surface Water and Energy Fluxes for GSMs, J. Geophys. Res., 99(D7), 14,415-14,428, Lohmann, D., E. Raschke, B. Nijssen, and D. P. Lettenmaier, "Regional Scale Hydrology: I. Formulation of the VIC-2L Model Coupled to a Routing Model", Hydrological Sciences Journal, 43(1), February 1998, pp McClelland, J.W., R. M. Holmes, and B. J. Peterson, 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: /2004JD Su, F., J.C. Adam, L.C. Bowling, and D.P. Lettenmaier, 2005, Streamflow Simulations of the Terrestrial Arctic Domain, J. Geophys. Res., 110. Yang, D., B. Ye, and D. Kane, 2004: Streamflow changes over Siberian Yenisei river basin, Journal of Hydrology, Vol. 296, no. 1-4, pp Ye, B., D. Yang, D. Kane, 2003: Changes in Lena river streamflow hydrology: human impacts vs. natural variations. Water Resources Research, 39 (7), Above: schematic for coupled hydrology (Liang et al. 1994, Su et al. 2005, Adam et al. 2007), routing (Lohmann et al. 1998), and reservoir (Haddeland et al. 2006) models. Below: comparison of observed and simulated monthly reservoir signatures at each of the evaluation gauging stations. Note: in the first column, thin lines indicate pre reservoir and thick lines indicate post reservoir streamflow. The ID numbers in the green circles refer to the green plusses in the study domain map (lower left). Simulation of Reservoir Effects on Seasonal and Annual Streamflow for the Lena, Yenisei, and Ob’ Rivers Jennifer C. Adam 1, Ingjerd Haddeland 2, Fengge Su 1, and Dennis P. Lettenmaier 1 1.Department of Civil and Environmental Engineering, Box , University of Washington, Seattle, WA Department of Geosciences, University of Oslo, BOX 1022 Blindern, 0315 Oslo, Norway AGU Fall Meeting, San Francisco, CA, December 2006 Step 1: Run VIC Model for Each Cell and Combine Runoff and Baseflow Step 2: Route to Reservoir and Bias Correct Seasonality using Pre- Reservoir Observed Data Step 3: Run Reservoir Model for each Operational Year by Maximizing Revenue from Hydropower Production Step 4: Rout Reservoir Releases and all other Basin Contributions to the Basin Outlet Objective 3. Reservoir Effects on Long-Term Trends Reservoir Capacity LENA Below Vilyuiskoe Above Vilyui Confluence Basin Outlet Below Krasnoyarskoe Boguchanskoe Below Irtish Confluence Basin Outlet Irtish at Omsk Below Novisibirskoe Basin Outlet YENISEI OB’ Monthly, seasonal, and annual observed flows were tested for trend for periods with varying lengths and start years between 1937 and The longest period for which the observed trend was significant (99%) was selected for each time interval, for each basin. The reconstructed products were then tested for trend for this same period. If there were no significant long-term (≥30 years) observed trends, results for this time interval are not shown (e.g. for the Ob’, annual, spring, summer, fall, etc…). The streamflow trend magnitudes for observed and two of the reconstructed products are shown in the bar plots. If the bars for the observed and reconstructed products are of similar magnitude, this would indicate that these changes were not caused by reservoir effects (e.g. Lena and Yenisei annual trends). If the bar for the observed trend is much greater than that for the reconstructed trend, this indicates that these changes were at least partially caused by reservoir effects (e.g. Lena and Yenisei winter trends). Below: comparison of monthly reservoir signatures for the four reconstructed streamflow products (ours, Mclelland et al. 2004; for the Lena, Ye et al. 2003; and for the Yenisei, Yang et al. 2004). Right: comparison of seasonal flows for the reconstructed and observed streamflow products. Note: vertical gray lines in the figures to the right indicate the year when filling began for each reservoir in the basin. LENA YENISEIOB’ Simulated McClelland Ye and Yang OBJECTIVES 1. To apply a coupled hydrology/reservoir/routing model to simulate the effects of reservoirs on streamflow seasonality and annual streamflow volume at the outlets of the Lena, Yenisei, and Ob’ basins. 2. To compare our method of estimating these effects to methods using only streamflow observations. 3. To separate out the effects of the reservoirs on long-term annual and seasonal streamflow trends. SimulatedMcClellandYe and YangObserved