Sub‐Seasonal Tree‐Ring Reconstructions for More Comprehensive Climate Records in U.S. West Coast Watersheds

Abstract

Tree-ring records are among the most important sources of information for understanding past precipitation, streamflow, and moisture-delivery patterns in western North America over the past millennium, providing the long-term context necessary for assessing recent changes in drought (Griffin & Anchukaitis, 2014), snowpack (Belmecheri et al., 2016), and storm tracks (Wise & Dannenberg, 2017). These records are used in water-management planning (Woodhouse & Lukas, 2006), to validate climate models (Otto-Bliesner et al., 2016), and to interpret historical events (Pederson et al., 2014). Wildfires, droughts, and floods linked to anthropogenic climate change add urgency to the need for paleoclimate records that can provide a more nuanced view of the range of possible climate conditions, including the timing of events. Existing tree-ring records of preinstrumental climate in western North America often reconstruct an annual cycle, commonly the water year (October-September), or a seasonal index value such as June-August PDSI that integrates conditions over a longer antecedent period (B. I. Cook et al., 2014). Differences identified between the tree-ring record and historical climate information, and between different environmental proxies, have been attributed to seasonal biases in these types of tree-ring records (Mock, 1991; Steinman et al., 2014). Many tree-ring reconstructions explicitly target a particular season, frequently the "cool season" (October-March or November-April) in western North America. Interpreting a fixed seasonal window as indicative of the year's climate can mask important subseasonal variation in moisture delivery. For instance, droughts of similar severity over the past century have varied significantly in which month most

Droughts, Pluvials, and Wet Season Timing Across the Chao Phraya River Basin: A 254‐Year Monthly Reconstruction From Tree Ring Widths and δ18O

“…However, annually‐resolved tree ring data still restrict how tree‐ring‐based paleoclimate reconstructions can be used in subsequent applications, where finer resolutions are desirable. For example, it is often difficult to compare annual climate reconstructions against historical events, because an event may have happened outside the target season of the reconstruction, or two opposite events (a flood and a drought) may be smoothed out by a reconstruction that targets the annual average (Wise, 2021). In addition, and specific to water resources, annual streamflow reconstructions have provided important insights into surface water availability, but cannot be used directly in water management models which require monthly, weekly, or even daily data (Galelli et al., 2021).…”

“…to the hydroclimate, and that there can be different time lags in hydrologic responses at various sites (Stagge et al, 2018;Stahle et al, 2020;Wise, 2021). A third approach uses intra-annual measurements of stable oxygen isotope ratios (δ 18 O) in tree ring cellulose to reconstruct intra-annual precipitation (Xu et al, 2016(Xu et al, , 2021.…”

Simulating the Impacts of Changes in Precipitation Timing and Intensity on Tree Growth

“…At the annual scale, trees often (although not always) capture dry conditions better than wet (Wise & Dannenberg, 2019), as water is no longer the limiting factor for growth beyond a certain threshold (Fritts, 1976). Intense but short‐duration precipitation events might not be reflected in tree‐ring widths due to this threshold effect or due to the mismatch in timing between growth functions in trees and seasonal moisture delivery (Wise, 2021). This could affect interpretation of past climates, yet very few tree‐ring reconstructions consider how the frequency and timing of precipitation might influence growth (O'Donnell et al., 2021).…”

The Flood Risk and Water Supply Implications of Seasonal Precipitation Reconstructions in Northern California

“…Several climate-sensitive tree species have been used for tree-ring chronology development and hydroclimatic reconstruction across western North America (e.g., Cook et al 1999;Meko et al 1980;Meko and Woodhouse 2005;Griffin and Anchukaitis 2014;Stahle et al 2020;Wise 2020;Woodhouse et al 2020;. These reconstructions are largely based on chronologies of total ring width (RW) that tend to integrate climate across several months during and preceding the tree growth season, resulting in reconstructions of climate variables like the Palmer Drought Severity Index (Cook et al 1999;Meko et al 1980), annual precipitation (Michaelsen et al 1987), and annual streamflow totals .…”