North American monsoon precipitation reconstructed from tree-ring latewood

[1] The North American monsoon is a major focus of modern and paleoclimate research, but relatively little is known about interannual- to decadal-scale monsoon moisture variability in the pre-instrumental era. This study draws from a new network of sub-annual tree-ringlatewoodwidth chronologies and presents a 470-year reconstruction of monsoon (June through August)standardized precipitation forsouthwestern North America.Comparison with an independent reconstruction of cool-season (October through April) standardized precipitation indicatesthat southwesterndecadaldroughts of the last five centuries were characterized not just by cool-season precipitation deficits, but also by concurrent failure of the summer monsoon. Monsoon drought events identified in the past were more severe and persistent than any of the instrumental era. The relationship between winter and summer precipitation is weak, at best, and not time stable. Years with opposing-sign seasonal precipitation anomalies, as noted by other studies, were anomalously frequent during the mid- to late-20th century.