Analysis of Streamflow in Upper Gunnison Basin: Is there a climate change signal?

Abstract:

Since the mid-1990s, most regions in the state of Colorado, including southwestern Colorado, have warmed by 2^oF. Climate projections for southwestern Colorado reveal several hydrologic and ecologically important changes over the upcoming decades, including decreases in annual runoff, increases in extreme precipitation events, earlier snowmelt and spring peak runoff, and increase in the duration of low flow period. Climate change is predicted to modify the shape of the stream hydrograph, i.e. timing and amount of natural streamflow, which is a concern because these changes could significantly affect ecosystem functioning, agriculture, wildlife, and recreation.

In this study, we analyze historical streamflow records from the Upper Gunnison Basin to distinguish any potential effects of climate change on streamflow, particularly in the last two decades. Daily streamflow data from six USGS gages were selected based on duration (60+ years ending in 2012) and completion of record, limited diversions/storage upstream from station, and broad dispersion throughout Gunnison County. We examined several different streamflow metrics to evaluate any changes in recent decades relative to long-term trend. We did not see a significant shift in the timing and amount of streamflow in the recent decades relative to the whole record. However for the 1991-2010 period, we discern slight earlier shifts in spring peak flow and in the timing of the low flow period in late summer/early fall at many of the gages. In this presentation, we discuss these results and explore the different drivers that affect the observed streamflow trends in this basin.