An Evaluation of Seasonal Precipitation and Its Influence on Streamflow in the Missouri River Headwaters Using Multi-Century Tree-Ring Reconstructions

Abstract

The impacts of warming temperatures and declining snowpack on seasonal water yields in the Missouri River Headwaters are not well understood, revealing a gap in our understanding of regional hydroclimate and drivers of streamflow within the Upper Missouri River basin. This study presents the first annually-resolved tree-ring reconstruction of spring precipitation for the Missouri River Headwaters. This reconstruction along with existing tree-ring reconstructions of April 1 snow-water equivalence (SWE) and natural water year streamflow are used to detect variable influences of winter and spring precipitation on streamflow over past centuries, and relative to the modern period. By analyzing the relationship between seasonal precipitation and water year streamflow in the Missouri River Headwaters subbasin, this study seeks to expand our knowledge based on the instrumental record alone. The results suggest that spring precipitation has been a more consistent influence on water year streamflow in the Missouri River Headwaters over past centuries than winter snowpack. The strong relationship between April 1 SWE values and water year streamflow in the Missouri River Headwaters observed over much of the twentieth century is not found to be a consistent feature of these multi-century paleorecords. These findings suggest that April 1 SWE may not always be a reliable indicator of water year streamflow. Instead, the hydroclimate influences of runoff and streamflow within the Missouri River Headwaters are likely more variable than the twentieth century instrumental records would seem to indicate.