Rocky Mountain hydroclimate: Holocene variability and the role of insolation, ENSO, and the North American Monsoon

摘要

Over the period of instrumental records, precipitation maximum in the headwaters of the Colored Rocky Mountains has been dominated by winter snow, with a substantial degree of interannual variability tinked to Pacific ocean-atmosphere dynamics. High-elevation snowpack is an important water storage that is care-fully observed in order to meet increasing water demands in the greater semi-arid region. The purpose tere is to consider Rocky Mountain water trends during the Holocene when known changes in earth's energy balance were caused by precession-driven insolation variability. Changes in solar insolation are thought to have influenced the variability and intensity of the El Nino Southern Oscillation (ENSO), Pacific Decadai Oscillation (PDO), and North American Monsoon and the seasonal precipitation balance between rain. and snow at upper elevations. Holocene records are presented from two high elevation lakes located ir. northwest Colorado that document decade-to-century scale precipitation seasonality for the past -7000 years. Compar-isons with sub-tropical records of ENSO indicate that the snowfall-dominated precipitation maxima ievel-oped -3000 and 4000 years ago, coincident with evidence for enhanced ENSO/PDO dynamics. During the early-to-mid Holocene the records suggest a more monsoon affected precipitation regime with reduced snowpack, more rainfall, and net moisture deficits that were more severe than recent droughts. The Hoiocene perspective of precipitation indicates a far broader range of variability than that of the past century and highlights the non-linear character of hydroclimate in the U.S. west.