Variability of Snow and Rainfall Partitioning Into Evapotranspiration and Summer Runoff Across Nine Mountainous Catchments

Understanding the partitioning of snow and rain contributing to either catchment streamflow or evapotranspiration (ET) is of critical relevance for water management in response to climate change. To investigate this partitioning, we use endmember splitting and mixing analyses based on stable isotope (O-18) data from nine headwater catchments in the East River, Colorado. Our results show that one third of the snow partitions to ET and 13% of the snowmelt sustains summer streamflow. Only 8% of the rainfall contributes to the summer streamflow, because most of the rain (67%) partitions to ET. The spatial variability of precipitation partitioning is mainly driven by aspect and tree cover across the sub-catchments. Catchments with higher tree cover have a higher share of snow becoming ET, resulting in less snow in summer streamflow. Summer streamflow did not contain more rain with higher rainfall sums, but more rain was taken up in ET.

Automated summary

Understanding the partitioning of snow and rain between streamflow and evapotranspiration is crucial for water management in the face of climate change. This study used stable isotope data to analyze the distribution of precipitation in nine headwater catchments. The results showed that most of the rainwater is evaporated, while a portion of the snowmelt contributes to summer streamflow. The tree cover and aspect were found to be the main factors influencing precipitation partitioning. More rainwater is taken up by evapotranspiration rather than contributing to summer streamflow.