Record Russian river discharge in 2007 and the limits of analysis

Abstract

The Arctic water cycle has experienced an unprecedented degree of change which may haveplanetary-scale impacts. The year 2007 in particular not only was unique in terms ofminimum sea ice extent in the Arctic Ocean but also was a record breaking year forEurasian river inflow to the Arctic Ocean. Over the observational period from 1936to 2006, the mean annual river discharge for the six largest Russian rivers was1796 km3 y−1, with the previousrecord high being 2080 km3 y−1, in 2002. The year 2007 showed a massive flux of fresh water from these six drainage basins of2254 km3 y−1. We investigated the hydroclimatological conditions for such extreme river discharge andfound that while that year’s flow was unusually high, the overall spatial patterns wereconsistent with the hydroclimatic trends since 1980, indicating that 2007 was not anaberration but a part of the general trend.We wanted to extend our hydroclimatological analysis of river discharge anomalies toseasonal and monthly time steps; however, there were limits to such analyses due to thedirect human impact on the river systems. Using reconstructions of the naturalizedhydrographs over the Yenisey basin we defined the limits to analysis due to theeffect of reservoirs on river discharge. For annual time steps the trends are lessimpacted by dam construction, whereas for seasonal and monthly time stepsthese data are confounded by the two sources of change, and the climate changesignals were overwhelmed by the human-induced river impoundments. We offertwo solutions to this problem; first, we recommend wider use of algorithms to‘naturalize’ the river discharge data and, second, we suggest the identification of anetwork of existing and stable river monitoring sites to be used for climate changeanalysis.