[A-HW23] 水循環・水環境

[AHW23-09] Positive feedback of Yenisei River discharge to Arctic amplification quantified with tree rings

*Irina P Panyushkina¹、David M Meko¹、Richard Thaxton¹、Alexander Shiklomanov² (1.University of Arizona、2.University of New Hampshire)

キーワード：Arctic Amplification, Tree Rings, Water Balance Model , River Discharge

The polar regions have been warming at an alarming rate for the last 25 years. Arctic climate is uniquely sensitive to changes in climate forcing, but also has large internal variability that needs to be understood and accounted for climate models. Our research focuses on capturing the climatic system perturbation with tree-ring proxies and quantifying the response of Yenisei River hydrology to the perturbation. The Yenisei River Basin (YRB) is the largest contributor of fresh water and heat to the Arctic Ocean. Sparsity of gauged observations and gaps in the records lead to bias and uncertainty in the modeling of YRB discharge, which is highly variable in space and time. Tree-ring networks from lower and upper reaches of the YRB were updated to 2019-2020 are applied to reconstruct annual (Oct-Sept) and winter (Nov-Apr) discharge of the Yenisei River from ca. 1780-1700 (Panyushkina et al. 2021). The reconstructed series doubles and triples the length of the gauged observations and places observed discharge variability in a multi-century context. Reconstructed discharge at the Kyzyl gauge (YRB upstream in Tuva) shows remarkable differences in the annual and seasonal discharge variability. Winter discharge has increased by 80% over the past 25 years; in contrast, annual discharge has fluctuated, but increased by only 7% over the same interval. Discharge reconstructions for the lower reaches of YRB near Turukhansk show different dynamics in the seasonal discharge variability. The streamflow–climate relationship for the two studied seasons is estimated with the New Hampshire water balance model using CRU monthly climate fields for the interval 1901-2019 (Fig.1). Although air temperature and precipitation track well the decadal variability of annual discharge, its trend is systematically underestimated by these climatic factors. The error increases significantly after 1960, and is even greater for the winter discharge. While the climate drivers decreased their rate of change during 1960–2000, the Yenisei base flow continued accelerating higher. We discuss possible impacts of fast-tracking permafrost thawing and intensified regime of boreal forest fires on the irregularity and unprecedented changes in streamflow across the YRB. The estimated YRB dynamics represent positive feedback of YRB hydrology to Arctic warming. Discharge changes triggered in an initial response to climate change are amplified by the internal perturbations in the system via permafrost degradation and forest fires.
Funding: This research was supported by U.S. NSF Polar Office program #1917503 and #1917515.
Reference: Panyushkina I.P., Meko D.M, Shiklomanov A., Thaxton R., Myglan V.V., Barinov V., Taynik A.V. 2021. Unprecedented acceleration of winter discharge of Upper Yenisei River inferred from tree rings. Environmental Research Letters, 10.1088/1748-9326/ac3e20.