Snowmelt-dominated basins exhibit strong relationships between snow water equivalent and seasonally accumulated streamflow in the Sierra Nevada of California

As watershed-scale snow water equivalent (SWE) data become more readily available from the NASA Airborne Snow Observatory (ASO), we can use these data to improve our understanding of the relationship between water resources tied up in the snow pack and resulting runoff for operational use. The contributions of snowmelt to streamflow are complex and this type of analysis helps bridge the gap between data collection and operational adoption of ASO products.

In this study, seasonally accumulated streamflow volumes as measured by water managers operating in 9 basins in the central Sierra Nevada of California were compared to basin-integrated SWE volumes derived from ASO SWE products (n=81). For all snow-dominated basins studied, the coefficient of determination (r²) was greater than 0.95, most greater than 0.98, giving water managers consistent inflow forecast uncertainties < 2% across a range of water year types. The slopes of these relationships represent an index similar to the Runoff Coefficient, a commonly used hydrologic metric, and varied from 0.6 to 1.1. Here, a value of 1 represents a 1:1 relationship between snow and resulting runoff, or 100% conversion of SWE to streamflow.

The pseudo-Runoff Coefficient for SWE values derived for each of the 9 basins were then compared to the physical characteristics of each basin such as elevation, vegetation, and melt rate. Mean elevation and tree line had the largest correlation with the pseudo-Runoff Coefficient for SWE. These results speak to the importance of elevation and vegetation in determining how water in the snow pack is transferred to river systems. A deeper understanding of the relationship between snow and resulting runoff will give water managers the ability to make more informed decision and lay the groundwork for observationally-based seasonal forecasting in basins with multiple ASO retrievals.