Effects of Drought and Climate Variability on Prehistoric Human Adaptation and Population in the Upper Colorado River Basin, USA

Keywords: Paleoenvironment, Drought, Prehistoric Population, Climate variability
Abstract Type: Poster Abstract

Abstract

Drought is often cited as a driver of prehistoric culture change. This study examines the dual importance of drought and increased variability in climate as drivers of culture change over the past 2300 years in the Western USA. Records of drought and climatic variability for this period are derived from a sediment core from Kannah Creek Fen on Grand Mesa, Colorado, and PDSI reconstructed from tree-rings for the past 2000 years. Because of the relatively marginal conditions that allow subalpine fens to persist, they are very sensitive to fluctuations in climate and the consequent hydrological responses. Loss on ignition at a 1cm sampling interval provides a record of changing fen primary productivity, which correlates to fluctuations in temperature. Humification of peat, which provides a record of water table fluctuation within the fen, provides a proxy for effective precipitation. These proxies document relatively abrupt transitions between hot, dry conditions to cool, wet conditions. These records of paleoenvironmental change are compared to a proxy record of regional prehistoric population provided by summed probability distributions of archaeological radiocarbon dates. Our data indicate that increased interannual climate variability, even in the absence of significant changes in baseline precipitation values, can be as powerful a driver of culture change as drought alone, and severe drought in conjunction with increased variability had a significant effect on culture and population in the Upper Colorado River Basin. The areal extent of drought conditions also had a significant effect on prehistoric populations.