LONG-TERM VARIABILITY OF THE PAN-ARCTIC HYDROLOGICAL BUDGET AND THE DECLINE IN HYDROLOGICAL MONITORING NETWORKS
SHIKLOMANOV, ALEXANDER I. University of New Hampshire.
Lammers, Richard B. University of New Hampshire.
Vorosmarty, Charles J. University of New Hampshire.
Peterson, Bruce J. Marine Biological Laboratory.
Holmes, Robert M. Marine Biological Laboratory.
McClelland, James W. Marine Biological Laboratory.
Russia, Canada, and the United States possess 92% of the non-ice covered pan-Arctic land area and contain the overwhelming majority of its monitoring stations. To estimate the current status of river discharge gauges across the pan-Arctic, data from the University of New Hampshire, the U.S. Geological Survey, the Water Survey of Canada, Environment Canada, and the Russian Hydrometeorological Service (Roshydromet) were used. The Arctic Ocean drainage basin is the best monitored in terms of freshwater flow to the coastal zone. During the 1980s, when the number of stations reached its maximum, about 74% of the total non-glacierized pan-Arctic basin area was monitored. Even under such favorable conditions no measurements were taken in large regions of the basin ranging from 40% in North America to 15% in Russia. The total area monitored decreased to 67% from 1986 through 1999 at a rate of 79% in Russia and 51% in North America because some important downstream gauges located mainly on medium and small-sized rivers were closed. The total number of gauges is also an important index of our capacity to develop high-resolution mapping of contemporary runoff. This constitutes an essential tool for monitoring progress of climate change and for studying the overall hydrological response throughout the region. Over the last 15 years, the number of hydrologic gauges serving the pan-Arctic reverted to that of the early 1960s. There is a significant difference in the decline of discharge networks of various sub-regions across the pan-Arctic drainage. The network cutbacks were especially severe in the Far East of Siberia and the province of Ontario, where 73% and 67% of river gauges were closed between 1986 and 1999, respectively.
An analysis of long-term variations of river discharge, made based on datasets up to year 2000, shows a sustainable increasing trend for all regions of the pan-Arctic basin except the Hudson Bay watershed. The average rate of the increase in discharge to the Arctic Ocean was 3.6 km3/year (1.9 km3/year in Eurasia and 1.7 km3/year in North America) for 1936-2000. The rate is significantly higher (10 km3/year) for the period when global air temperature had a fast rise since 1976. Especially high values of river inflow to the ocean are observed since 1986. The mean annual discharge for 1986-2000 was about 200 km3/year greater than for 1936-85. Thus additional freshwater discharge for this period was 2800 km3. This volume approximately equals the total annual inflow from Eurasia. An integrated analysis of air temperature, precipitation and runoff was carried out for the 10 largest river basins representing a wide variation in geography. All these river basins show the air temperature increasing during last 10-20 years. The greatest runoff increase is observed for the large European rivers (Northern Dvina, Pechora) where it results from significant precipitation increase. The largest Siberian river basins, which have wide permafrost extent, demonstrate the increase in runoff despite no trend or a decreasing trend in precipitation. It is likely the result of several components such as permafrost melting, a shorter winter period, an increase in ground water storage and a more rapid spring snow melt (such as the spring 2001 Siberian floods). Further research is going to be focused on water budget simulations for representative, undisturbed watersheds located in various climate regions to investigate the effect of global change on river runoff formation across the pan-Arctic drainage basin and river discharge to the ocean.
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