A paleo perspective on hydroclimatic variability in the western United States

Aquatic resources management has become increasingly challenging as human demands on water supplies compete with the needs of natural ecosystems, particularly in arid lands. A wide range of factors, both natural and human, influence aquatic environments, but an important underlying component is climate variability. Instrumental records of hydroclimatic variability from precipitation, streamflow, and snowpack are limited to 100 years or less in most areas of the western U.S., and are too short to provide more than a subset of the full range of natural climate variability. Paleoclimatic proxy data from a variety of sources can be used to extend instrumental records of climate back centuries to tens of thousands of years and longer. In this review, four drought events over the past three millennia, each documented with a number of proxy records, illustrate natural hydroclimatic variability characteristics over the western U.S. Although a small sample of paleoclimate data, these four events exemplify the wide range of natural hydroclimatic variability over space and time. Climate is now, and will continue to be, impacted by human activities, but natural climatic variability will likely be an important underlying factor in future climate variability and change.