Snow simulation for the Rangeland Hydrology and Erosion Model

Authors: BROXTON, P. - University Of Arizona; Goodrich, David - Dave; GUERTIN, D.P. - University Of Arizona; Williams, Christopher - Jason; Unkrich, Carl; HERNANDEZ, M. - University Of Arizona; FULLHART, A.T. - University Of Arizona; HOUDESHELL, C.A. - Natural Resources Conservation Service (NRCS, USDA); SEYFRIED, M. - Retired ARS Employee; METZ, L. - Natural Resources Canada

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2024
Publication Date: 9/10/2024
Citation: Broxton, P., Goodrich, D.C., Guertin, D., Williams, C.J., Unkrich, C.L., Hernandez, M., Fullhart, A., Houdeshell, C., Seyfried, M., Metz, L. 2024. Snow simulation for the Rangeland Hydrology and Erosion Model. Journal of Hydrology. 643. Article 131934. https://doi.org/10.1016/j.jhydrol.2024.131934.
DOI: https://doi.org/10.1016/j.jhydrol.2024.131934

Interpretive Summary: Runoff and erosion modeling of high elevation rangelands must account for water input as rainfall and snowmelt, particularly where rain-on-snow or heavy snowfall are common. This study developed a new approach to effectively represent rainfall and snowmelt contributions to hillslope runoff, soil loss, and sediment yield predictions by the Rangeland Hydrology and Erosion Model (RHEM). Assessment of the new approach found that more effective partitioning of water inputs from rain and snow can reduce predicted runoff and sediment responses at the annual time scale by more than 20% relative to treating all water input as rainfall. For rain-on-snow events, the new approach found runoff and sediment responses can either be enhanced or muted depending on variability in storm characteristics and snowpack characteristics. Overall, the new approach more appropriately partitions water input and provides more realistic timing and magnitude of cold-season hydrologic and erosion processes in snow-dominated uplands relative to that of previous RHEM versions. Further research is needed to improve effective representation of cold-season effects on soil erodibility. However, the advances noted above provide land managers and other end users an enhanced RHEM tool for applications to high elevation snow-dominated rangelands.

Technical Abstract: In the western US, the majority of rangelands receive snowfall. Yet, a commonly used tool to assess rangeland vulnerability to erosion, the USDA’s Rangeland Hydrology and Erosion Model (RHEM) is run using long-term simulated climate inputs that assume that all precipitation occurs as rainfall. This can be problematic for areas that receive heavy snowfall or substantial rain-on-snow events. In this research, we have developed an efficient snow module for RHEM, called RHEM-Snow, which partitions precipitation between rainfall and snowfall, simulates snowpack accumulation and ablation, and passes net water input (consisting of rainfall, snowmelt, or both) to RHEM. In some areas, the inclusion of the snow module can reduce annual overland flow runoff and erosion estimates by more than 20% of the total annual overland flow runoff and erosion produced without the snow module (or by as much as 10-50 mm/year for overland flow runoff or >100 kg/ha-yr for erosion). Reductions are primarily due to the reclassification of precipitation events from rainfall in RHEM to snowfall in RHEM-Snow, which reduces overland flow runoff and erosion because melting of accumulated snowfall usually has lower intensity than many precipitation events. Hydrologic responses to rain-on-snow events can either be enhanced or muted depending on the characteristics of the storm and the snowpack, as sometimes the snowpack can absorb the precipitation inputs, and sometimes snowmelt enhances the precipitation inputs. Because of this mixed impact, the average difference in erosion caused by rain on snow events is relatively small compared to corresponding events where only the liquid phase is considered. Further study is needed of the complex erosion processes under snowpack and frozen soil / variable saturation conditions. Overall, RHEM-Snow provides more realistic timing and magnitude of overland flow runoff and erosion in cold environments, better satisfying the conditions for RHEM applications.