Capturing season‐specific precipitation signals in the northern Rocky Mountains, USA, using earlywood and latewood tree rings

Abstract

Douglas-fir (Pseudotsuga menziesii Mirb. Franco) total width, earlywood, and latewood tree ring chronologies were developed from six lower forest border sites in the northern Rocky Mountain region of central Idaho and southwestern Montana, USA, to assess the potential for season-specific moisture reconstructions. These long-lived arid-site trees share strong between-tree and between-site coherence, and subannual tree ring chronologies reliably span the past seven centuries. Mapping spatiotemporal patterns in northern Rocky Mountain precipitation highlighted winter-and summer-dominated precipitation regimes that transition along a west to east gradient. When Douglas-fir tree rings were compared with instrumental climate records, season-specific correlations emerged between earlywood and latewood. Total width, earlywood, and latewood shared the most statistically significant monthly correlations with April-June precipitation, whereas variability in adjusted latewood was tuned to June-August precipitation. Principal component analysis indicated that the leading mode of common variance for earlywood and adjusted latewood explained 65% and 55% variance in the chronologies, respectively. Pearson's correlations between earlywood principal component one and the northern Rocky Mountain precipitation field showed that annual (July-June) and spring (April-June) precipitation exhibited the strongest pattern of significance in central Idaho and southwestern Montana valleys and the Snake River Plain. Summer precipitation (June-August) was correlated with adjusted latewood principal component one and was particularly pronounced along and east of the continental divide in southwestern Montana. These results indicate that Douglas-fir earlywood and adjusted latewood tree rings in the northern Rocky Mountains retain season-specific precipitation signals and may be helpful for studying historical precipitation within the winter-summer transition zone.

High sensitivity of gross primary production in the Rocky Mountains to summer rain

“…Proxy and instrumental records of cold and warm season precipitation amounts show that the two generally vary independently of one another [ Crawford et al , ; Griffin et al , ; Dannenberg and Wise , ; Anderson et al , ] (supporting information Figure S6). However, an analysis of seasonal precipitation trends over the last three decades shows declines in both snowpack and summer rain that has resulted in region‐wide stability in their relative contributions to annual precipitation (supporting information Figure S7).…”

“…Previous works on ecohydrology in the western U.S. have utilized a variety of approaches including, eddy covariance (EC) [Schwalm et al, 2012;Hu et al, 2010;Biederman et al, 2016;Hsu et al, 2012;Anderson-Teixeira et al, 2011], tree rings [Cook et al, 2004;LaMarche and Stockton, 1974;Woodhouse, 2003;Crawford et al, 2015;George and Ault, 2014;Dannenberg and Wise, 2016], and remote sensing [Trujillo et al, 2012;Barichivich et al, 2014;Jin and Goulden, 2014]. Although each method has provided important perspectives, they have limitations which support the need for new approaches.…”

A 500‐Year Tree Ring‐Based Reconstruction of Extreme Cold‐Season Precipitation and Number of Atmospheric River Landfalls Across the Southwestern United States

“…Recent efforts toward this end have shown promise (Wise & Dannenberg, 2017). However, larger summer precipitation totals and lower evaporation rates in the Pacific Northwest will require additional care in isolating the wintertime signal, which is becoming increasingly possible by using earlywood and latewood chronologies (Crawford et al, 2015).…”

Seasonal climate signals from multiple tree ring metrics: A case study of Pinus ponderosa in the upper Columbia River Basin

“…In the western U.S., for example, climate change has led to significant reductions in mountain snowpack which are nearly unprecedented in historical and paleoclimate records [ Barnett et al ., ; Mote et al ., ; Pederson et al ., ; Luce et al ., ]. Declining snowpacks, combined with seasonality shifts, are a major challenge for water resource managers in these regions [ Hamlet and Lettenmaier , ; Leung et al ., ; Crawford et al ., ], increasing the need to understand historical variation of precipitation and drought on subannual time scales. These changes in hydroclimate will also have significant consequences for the functioning of terrestrial ecosystems [ Settele et al ., ], including likely changes in vegetation distribution, fire regimes, and carbon uptake and storage [ Boisvenue and Running , ; Rogers et al ., ; Notaro et al ., ; Jiang et al ., ].…”