The Western U.S. derives critical water resources from the upper Colorado River Basin, which has produced below average water supplies over the past eight years. Is this drought unusual? How long can it be expected to last? Will rising temperatures exacerbate the problem? These questions have gained renewed importance in recent months as researchers forecast warmer and drier conditions in the Western U.S. This study will provide some answers by examining the duration and severity of drought in part of the Upper Colorado River Basin (Uinta Mountains, Utah) during the Medieval Warm Period (MWP; ca. A.D. 900- A.D. 1100) as captured in tree-ring and lake sediment records. The MWP was the most recent interval during which temperatures were sustained at levels now forecast to occur from anthropogenic warming. Identifying the variability of water supplied by the Uinta Mountains during the MWP is critical for future water management planning in the region and for larger issues of climate modeling and drought management in the Western U.S. The impacts of dramatic, prolonged warming on water supplies in this key water source region are presently poorly understood because of the complex interactions of changes in evaporation, seasonal precipitation, and ocean surface temperatures which impact western US climate. In particular, the Uinta Mountains are a problematic area as they lie between the centers of action for hydrological changes caused by Pacific sea surface temperature shifts. This new work will add to doctoral dissertation research already underway that is obtaining knowledge of drought and aridity in the Uinta Mountains over the past 800 years using tree-rings (annual resolution) and over the past ~13,000 years using the fossil remains of diatoms (algae sensitive to environmental changes) in a lake sediment core (centennial resolution). This additional research will extend the tree-ring record further back in time to include the MWP and will examine the recent diatom record at higher temporal resolution, again capturing the MWP.
The work described here is the first joint tree-ring and high-resolution diatom study of drought in the Uinta region. This two-pronged research approach is more effective than single-method studies because it allows results to be independently confirmed. This research will also develop the first diatom-based drought model for the intermontane region of the western United States. As the sole body of work identifying paleo-drought patterns in the Uinta Mountains, this study will contribute essential knowledge for understanding basin-wide drought in the Colorado River as well as regional water shortages. An analysis of drought conditions during the MWP is very timely considering the continuing multi-year drought in the Western United States and predictions for increased aridity in the region as global temperatures continue to rise. Broader impacts of this research include providing essential knowledge to water and land managers for future resource planning, sharing data with other researchers to develop more comprehensive drought records for the Colorado River Basin, community drought education, and providing undergraduate student research opportunities.
