Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Streamflow Changes over the Large Siberian Watersheds: Natural Variation vs. Human Impact
Daqing Yang1, Douglas L. Kane2, Baisheng Ye3
1Water and Environment Research Center, University of Alaska Fairbanks, 457 Duckering Building, UAF, Fairbanks, AK, 99775, USA, Phone 907-474-2468, Fax 907-474-7979, ffdy@uaf.edu
2Water and Environment Research Center, University of Alaska Fairbanks,, 457 Duckering Building, UAF, Fairbanks, AK, 99775, USA, Phone 907-474-7808, Fax 907-474-7979, ffdlk@uaf.edu
3River and Environmental Engineering Lab , University of Tokyo, Bunkyo-ku, Tokyo, 113-8656, Japan, Phone 81-035-841-8874, Fax 81-035-841-6130
Observational records show significant climate change in the high latitude regions over the past several decades. Hydrologic response of the large northern watersheds to climate change and variation is one of the key issues in understanding atmosphere-land interactions in the northern regions. Examination and documentation of changes in the major northern rivers are also important to studies of global change, regional water resources and distribution of ecosystems. In order to describe the seasonal regime of river streamflow, and to document significant streamflow changes induced by human activities (particularly reservoirs) and by natural variations/changes, this study analyzes the long-term monthly streamflow records over the past 40-50 years for the large Siberian watersheds, such as the Lena, Yenisei, and Ob rivers. The results show significant changes in streamflow characteristics. These include amount and timing of snowmelt runoff, summer season discharge, and increases in winter discharge over most of the watersheds. These changes may indicate a hydrologic regime shift due to recent climate warming over the northern regions. They may also be related to changes in permafrost conditions and influenced by human activities.
Detail analyses of Lena basin monthly streamflow data show that the upper streams of the watershed, without much human impact, experience a runoff increase in winter, spring and (particularly) summer seasons, and a discharge decrease in fall season. These changes in seasonal streamflow characteristics indicate a hydrologic regime shift toward early snowmelt and higher summer streamflow perhaps due to regional climate warming and permafrost degradation in the southern parts of Siberia. The results also demonstrate that reservoir regulations have significantly altered the monthly discharge regime in the lower parts of Lena river basin. Because of a large dam in west Lena river, summer (high) flows at the outlet of the Vilui valley have been reduced by up to 55% and winter (low) flows have been increased by up to 30 times. These alterations, plus streamflow changes in the upper Lena regions, lead to strong upward trends (up to 90%) in monthly discharge at the basin outlet during the low flow months and weak increases (5-10%) in the high flow season. Monthly flow records at the basin outlet have been reconstructed by a regression method to reduce reservoir impacts. Trend analyses and comparisons between the observed and reconstructed monthly flows show that, because of reservoir regulations, discharge records observed at the Lena basin outlet do not always represent natural changes and variations. They tend to underestimate the natural runoff trends in summer and overestimate the trends in both winter and fall seasons. Therefore, cold season discharge increases at the Lena basin outlet are not all natural-caused, but the combined effect of reservoir regulation and natural runoff changes in the unregulated upper sub-basins. This study clearly illustrates the importance of human activities in regional and global environment changes. More efforts are needed to examine human impacts in other large high-latitude watersheds.
Abstract Categories: Changes on Land
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