Know Your Watershed: Cumulative Precipitation & Streamflow
We’re on track to have a banner year when it comes to rain and snow. While we don’t know how much has fallen on each and every acre, we have a good idea of the big picture from cumulative precipitation (aka accumulated inches of water from rain and snow in any one spot over a given period of time). This is measured at weather stations, SNOTEL sites, and citizen scientists’ backyards across Ouray County. For the current 2023 water year, between Oct 1, 2022 and Feb 24, 2023, cumulative precipitation ranged from 7 inches down low in Ridgway to 23 inches at the top of Red Mountain Pass.
Has all of this rain and snow led to big flows in the Uncompahgre River? Not exactly. Its flows are typically lowest in the winter because most snow at higher elevations doesn’t run off the land; it builds up into snowpack until melting begins in the spring. Then, thirsty plants and soils take up much of the melted water and rain that falls. Some evaporates, and some goes to deeper groundwater, but a lot of what runs off the surface makes its way into channels, streams, and finally the Uncompahgre River.
This circuitous route adds delays and detours for rain and snow on its journey to the river. You can see these effects by comparing Ridgway’s cumulative precipitation graph for the 2022 water year with the Uncompaghre’s flow measured just downstream of Ridgway. The precipitation line steps up with each storm, but the streamflow line is a jagged variation on a single large wave.
National Weather Service 2022 Water Year cumulative precipitation graph for Ridgway. Link to climate data
Even though precipitation is the ultimate source of the river’s water, it’s not a clearcut, immediate connection to the level of streamflows, especially in winter. But a dry year will have less flow, a wet year more flow, and in summer months, the short-term peaks in the streamflow curve are often related to individual storms. It’s just the when, where, and how much that are a bit of a wildcard dealt by the watershed and Mother Nature.
USGS stream gage data showing streamflow measured near Ridgway for the 2022 water year. Link to gage data
