Annual Thermal Regimes of Headwater Streams within the Colorado River Basin

Understanding how stream temperatures respond to climate change will have important implications on how we manage native fish species found in isolated headwater streams. While there has been considerable effort to describe summer thermal regimes within small streams, much less attention has been paid to winter, spring, or fall temperatures. To this end we evaluated the annual thermal conditions of headwater streams and the air temperatures proximate to these streams within the range of the Colorado River Cutthroat Trout.  Our analysis suggests the annual relationship between air and water temperature is not linear but that it does differ among streams.  Furthermore summer stream temperature metrics are more strongly related to air temperature, solar radiation, elevation, watershed area, shade, groundwater input, slope and aspect than are winter temperatures. We did, however, find that cold air pooling occurred during both summer and winter time periods. Our work documents the value of using multiple stream temperature metrics to anticipate a stream’s response to increasing incoming solar radiation rather than reliance on a single metric derived during the summer. A better understanding of the annual thermal regime in streams should help managers make improved decisions concerning trout restoration in the Rocky Mountains.