Low‐frequency variability of precipitation in the North American monsoon region as diagnosed through earlywood and latewood tree‐ring chronologies in the southwestern US

Abstract

Recent studies have pointed out the statistical occurrence of dual-season droughts detected in tree-ring chronologies over the southwestern US region that is not well described by instrumental observed records of the 20th century. In this study, a multi-statistical approach that evaluates persistent dual-season drought using a mode-of-variability oriented approach is proposed, considering a new network of tree-ring earlywood (EW)-and latewood-adjusted (LW adj ) chronologies from throughout southwestern North America. To determine dominant patterns of spatiotemporal variability, empirical, orthogonal functions, canonical correlation analysis, and multi-taper-method singular value decomposition analyses were applied, with focus on variability from inter-annual to centennial periods and highlighting the multi-decadal signals inherent to proxy record network. During the instrumental period, we demonstrate that EW and LW adj networks of tree-ring chronologies are able to capture the associated precipitation responses of cool and warm season atmospheric teleconnections. Considering the four-century period of the complete tree-ring network, we explore the possibility of a dual summer-winter variability signal in the low-frequency climate regime. EW and LW adj seem to be coherent in-phase at the very low-frequency scale (50-100 years spectral band). This provocative result is supported by major historic documented multi-year droughts of the region since 1650. Thus, the temporal variation of these chronologies time series and its associated spatial pattern strongly suggest that this low-frequency mode might represents an important spatiotemporal variation of droughts in the Southwest; however, the source of this signal is still an open question and of great interest for drought planning and resource management in the region.

Legacies of La Niña: North American monsoon can rescue trees from winter drought

“…In the dataset used here, abnormally wet Julys tended to follow dry winters, which could underlie NAM effects on growth during La Niña periods due to likely incidental (Griffin et al, 2013) correlations between winter and monsoonal precipitation extremes (Stahle et al, 2009). Given our results, monsoon failure following a La Niña winter could have particularly severe impacts on southern populations, and inphase cool and warm-season precipitation anomalies are associated with major long-term drought events in the tree-ring record over the last four centuries (Carrillo, Castro, Woodhouse, & Griffin, 2016).…”

Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree‐ring stable isotopes

“…The autocorrelation structure was conspicuous in trees from multiple sites across the NAM climate gradient and best seen in the EW1 fraction, suggesting that this low-frequency component is more likely coupled to synoptic, widespread (and potentially cyclic) climatic influences on winter precipitation, rather than variance in the cross-gradient influences of the NAM. Our observations of a clear and general autocorrelation in the δ 13 C of EW1 and LW suggest that the common seasonal low-frequency component of the climate signal (Carrillo, Castro, Woodhouse, & Griffin, 2015) is detected in the iWUE expressed during the respective spring and summer seasons of active carbon assimilation. These conclusions on the shared autocorrelation in partial ring widths are similar to those derived in previous studies using partial ring width chronologies (Carrillo et al, 2015;Griffin et al, 2013).…”

“…and LW suggest that the common seasonal low-frequency component of the climate signal (Carrillo, Castro, Woodhouse, & Griffin, 2015) is detected in the iWUE expressed during the respective spring and summer seasons of active carbon assimilation. These conclusions on the shared autocorrelation in partial ring widths are similar to those derived in previous studies using partial ring width chronologies (Carrillo et al, 2015;Griffin et al, 2013). The F I G U R E 7 Consistency of the observed difference of δ 18 O ratios, and Δ 18 O ratios, between EW1 and LW with the difference modeled by a coupled isotope-climate model.…”

Navajo Nation, USA, Precipitation Variability from 2002 to 2015

“…Water year precipitation totals across the Navajo Nation are also strongly influenced by summer season rainfall, however, summer storms are the dominant source of precipitation in four of the five cluster group regions. Variation in warm‐season precipitation totals is much less coherent across the region, consistent with the more localized, convective nature of the monsoonal precipitation arriving during the summer season (Favors and Abatzoglou ; Carillo et al ). Although no strong teleconnections were observed for summer precipitation variability, our analysis showed that pressure patterns over the western interior correlate with summer precipitation amounts.…”