IMPACTS OF EARLIER SNOWMELT ON PATTERNS OF STREAMFLOW IN SOUTHWEST COLORADO RIVERS

Several recent studies show a significant trend toward earlier snowmelt and therefore earlier peak streamflows in mid- to high-elevation, snowmelt dominated western streams. Previous work has, out of necessity, focused on streams with little anthropogenic influence in the form of diversions and dams. With clear shifts in timing now evident, it is important to understand the ramifications of earlier peak flows on streams and rivers across a range of elevations and human impacts. In this preliminary study we pair data from USGS stream gages from southwest Colorado on rivers at similar elevations and with similar drainage basin areas but with different levels of human impact. We use raster based analysis to show graphically the strikingly different patterns of high and low flow in two time dimensions: both across water years and across the 30-100 year period of record for each gage. Using these techniques, we show that the signal from warming climate creates different patterns of discharge depending on the position in the drainage basin and human use. Once identified, these patterns yield new and often unexpected insights into the changing behavior of flowing surface waters in the mountainous west.