Application of New Precipitation and Reconstructed Streamflow Products to Streamflow Trend Attribution in Northern Eurasia

Abstract

River runoff to the Arctic Ocean has increased over the last century, primarily during the winter and spring and primarily from the major Eurasian rivers. Some recent studies have suggested that the additional runoff is due to increased northward transport of atmospheric moisture (and associated increased precipitation), but other studies show inconsistencies in long-term runoff and precipitation trends, perhaps partly due to biases in the observational datasets. Through trend analysis of precipitation, temperature, and streamflow data, the authors investigate the extent to which Eurasian Arctic river discharge changes are attributable to precipitation and temperature changes as well as to reservoir construction and operation between the years of 1936 and 2000. Two new datasets are applied: a gridded precipitation product, in which the low-frequency variability is constrained to match that of long-term bias-corrected precipitation station data, and a reconstructed streamflow product, in which the effects of reservoirs have been minimized using a physically based reservoir model. It is found that reservoir operations have primarily affected streamflow seasonality, increasing winter discharge and decreasing summer discharge. To understand the influences of climate on streamflow changes, the authors hypothesize three cases that would cause precipitation trends to be inconsistent with streamflow trends: first, for the coldest basins in northeastern Siberia, streamflow should be sensitive to warming primarily as a result of the melting of excess ground ice, and for these basins positive streamflow trends may exceed precipitation trends in magnitude; second, evapotranspiration (ET) in the warmer regions of western Siberia and European Russia is sensitive to warming and increased precipitation, therefore observed precipitation trends may exceed streamflow trends; and third, streamflow from the central Siberian basins should respond to both effects. It is found that, in general, these hypotheses hold true. In the coldest basins, streamflow trends diverged from precipitation trends starting in the 1950s to 1960s, and this divergence accelerated thereafter. In the warmest basins, precipitation trends consistently exceeded streamflow trends, suggesting that increased precipitation contributed to increases in both ET and streamflow. In the central basins, permafrost degradation and ET effects appear to be contributing to long-term streamflow trends in varying degrees for each basin. The results herein suggest that the extent and state of the permafrost underlying a basin is a complicating factor in understanding long-term changes in Eurasian Arctic river discharge.

Relevance of Hydro-Climatic Change Projection and Monitoring for Assessment of Water Cycle Changes in the Arctic

“…Serreze et al (2002) however found only low correlation between P-E and runoff across the pan-Arctic drainage basin, except for the Lena basin. Several studies have discussed a possible contribution of melting permafrost to increased runoff (Serreze et al 2002;Adam and Lettenmaier 2008;Dyurgerov et al 2010), but at least for the Eurasian Arctic, the total volumes of melting permafrost that are needed to explain the long-term runoff increases seem unrealistic (McClelland et al 2004). …”

“…Most likely, a combination of several factors has generated the observed runoff changes, and that combination may vary from basin to basin (Adam and Lettenmaier 2008).…”

Integrated assessment of changes in freshwater inflow to the Arctic Ocean

“…For both these extreme cases, no change in U is assumed. In reality, the sea level rise contribution from the river R increase is likely to be somewhere in between these two limiting cases and to be a combination of changes in P − E and M + F, with different relative importance in different geographical regions [Adam and Lettenmaier, 2008]. [24] Several studies have identified increases in poleward moisture transport, which imply that precipitation P has increased and may be a main driver of increasing river runoff in the Arctic [Dyurgerov and Carter, 2004;McClelland et al, 2004McClelland et al, , 2006.…”

“…[25] With regard to the dW/dt term in the river basins, other recent studies have indicated that it may be significantly nonzero because of both ongoing permafrost thawing [Adam and Lettenmaier, 2008;Lyon et al, 2009;Lyon and Destouni, 2010] and increasing groundwater flow into rivers in Arctic and subarctic basins [Smith et al, 2007]. New analysis of land water storage from Gravity Recovery and Climate Experiment satellite data also indicates negative dW/dt terms for some major Arctic basins, although data are as yet available only for a few years [Ramillien et al, 2008].…”

The Variable Infiltration Capacity Model, Version 5 (VIC-5): Infrastructure improvements for new applications and reproducibility

“…The model has been used for numerous water and energy balance studies in the U.S. (Abdulla and Lettenmaier, 1997;Nijssen et al, 1997), the Arctic (Adam and Lettenmaier, 2008;Su et al, 2005;Tan et al, 2011;Hamman et al, 2016) and globally (Nijssen et al, 2001a, b, c;Sheffield et al, 2009). One result of these 20 studies has been refinement of the model to better represent key hydrological processes Cherkauer et al, 2003;Liang et al, 1996Liang et al, , 1999.…”