Impact of high flows of an Arctic river on ring widths of floodplain trees

Abstract

The tree-ring signal for flooding along the Ob River, a large Arctic River in western Siberia, is investigated using a combination of floodplain tree-ring sites from riparian and non-riparian settings. A conceptual model is presented contrasting tree-growth responses of riparian and non-riparian trees to unusually severe flooding. A set of five riparian ( Salix and Populus) tree-ring chronologies is developed and used in combination with existing floodplain non-riparian Larix and Pinus chronologies in a binary classification tree (CT) model to classify high-flood years, defined as a Salekhard water-level gage reading in the seasonal window from May 1 to August 31 of above 470 cm for 82 or more consecutive days. Correlation and regression identifies a nonlinear relationship of riparian ring widths to discharge and flooding: higher annual discharge generally leads to higher growth, but the relationship reverses in extreme-flood years. Micrographs highlight the suppression of width and occasional distortion of cell anatomy in selected trees. CT modeling guided by cross-validation yields a CT model with a primary split on the riparian ring width and secondary split on the non-riparian ring width. The model successfully identifies four of the eight most severe high-flow years, 1934–2014. The model further identifies two years (1885 and 1914) before the start of the gaged record in 1934 as high-flow years. No appreciable difference is found in frequency of high-flow years before and after 1956, when the first major reservoirs began filling upstream of the Lower Ob. The CT modeling approach is proposed as a novel approach to dealing with nonlinearity in reconstructing flood history of Arctic rivers from tree rings.

Unprecedented acceleration of winter discharge of Upper Yenisei River inferred from tree rings

“…Stepwise regression of the selected tree-ring chronologies with Yenisei discharge at the Kyzyl gauge finds two seasonal groupings: (a) a 6 month period beginning in November of the preceding growth year and ending in the following April with the strongest signal (R 2 = 0.52, F = 14.14, p < 0.00001) (table 2), and (b) a 12 month window beginning in October of the preceding growth year with a weaker signal (R 2 = 0.26, F = 6.08, p < 0.001). Although the signal of the second seasonal grouping was weaker, it is still comparable with signals obtained for the Ob River basin from the Eurasian pan-Arctic (Agafonov et al 2016, Meko et al 2020). Both signals are sufficiently strong to justify the reconstruction effort.…”

“…Tree-ring data have long been useful to hydrological studies in arid regions (Schulman 1945). Yet, only recently has this potential been tested in cold regions (MacDonald et al 2007, Agafonov et al 2016, Meko et al 2020 where in some settings trees respond to air temperature variation specifically driven by water levels rather than to precipitation reflecting soil moisture stress. In this study we aim (a) to reconstruct seasonal discharge of the Yenisei River at the upper reaches situated in the discontinuous permafrost, and (b) to examine the long-term variability of the streamflow in response to climate change particularly during the winter season, when discharge trends have been pronounced.…”

Riparian forest productivity decline initiated by streamflow diversion then amplified by atmospheric drought 40 years later

“…Riparian dendrochronology is a tool for revealing historical relationships between streamflow and connected ecosystems (Philipsen et al, 2018; Stella et al, 2013), especially in semi‐arid regions where streamflow replenishes alluvial groundwater. Cottonwood ring width is often more highly correlated to flow than to local precipitation along free‐flowing rivers (Johnson et al, 1976; Meko et al, 2015), and tree‐ring width can be used as a proxy for discharge (Meko et al, 2020; Schook, Friedman, & Rathburn, 2016). Regulating streamflow can force trees to become more dependent on local precipitation (Reily & Johnson, 1982) or lead to tree death if changes are too extreme and local precipitation is insufficient (Cooper et al, 2003).…”

Informing Seasonal Proxy‐Based Flow Reconstructions Using Baseflow Separation: An Example From the Potomac River, United States

“…Estimating return periods for extreme low‐flow and flood events may result in large associated uncertainties due to the relatively short observational records of streamflow (Koutsoyiannis & Montanari 2007), especially in regions where climatological influence on streamflow variability has a low‐frequency component (e.g., Enfield et al., 2001). Paleoclimate reconstructions based on tree‐ring chronologies have been used to extend instrumental streamflow data across the world (e.g., Gou et al., 2007; Meko et al., 2020; Urrutia et al., 2011; Rao et al., 2018). Notable reconstructions from the United States include past estimates for the San Joaquin‐Sacramento River (Meko et al., 2001) and the Colorado River (e.g., Woodhouse et al., 2006).…”