Rangeland hydrology and erosion handbook: the RHEM guide

Authors: Weltz, Mark; Hernandez, Mariano; NEARING, MARK; SPAETH, KEN - NATURAL RESOURCES CONSERVATION SERVICE (NRCS, USDA); PIERSON JR, FREDERICK; Williams, Christopher - Jason; AL-HAMDAN, OSAMA - TEXAS A&M UNIVERSITY; NOUWAKPO, S. KOSSI - UNIVERSITY OF NEVADA; Armendariz, Gerardo; WEI, HAIYAN - UNIVERSITY OF ARIZONA; Goodrich, David - Dave; GUERTIN, PHILLIP - UNIVERSITY OF ARIZONA; Unkrich, Carl; Polyakov, Viktor; MCGWIRE, KENNETH - DESERT RESEARCH INSTITUTE; Nesbit, Jason; FRAZIER, GARY - RETIRED ARS EMPLOYEE; JOLLEY, LEONARD - RETIRED NON ARS EMPLOYEE; STONE, JEFF - RETIRED ARS EMPLOYEE

Submitted to: Agriculture Handbook
Publication Type: Government Publication
Publication Acceptance Date: 9/13/2021
Publication Date: 9/13/2021
Citation: Weltz, M.A., Hernandez Narvaez, M.N., Nearing, M.A., Spaeth, K.E., Pierson Jr, F.B., Williams, C.J., Al-Hamdan, O.Z., Nouwakpo, S., Armendariz, G.A., Wei, H., Goodrich, D.C., Guertin, P., Unkrich, C.L., Polyakov, V.O., McGwire, K., Nesbit, J.E., Frazier, G., Jolley, L., Stone, J. 2021. Rangeland Hydrology and Erosion Handbook: The RHEM Guide (NRCS Publication No 647, Title 190). Natural Resources Conservation Service (NRCS). 1-80. Available: https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=47163

Interpretive Summary: Soil loss rates on rangelands are considered one of the few quantitative indicators for assessing rangeland health and conservation practice effectiveness. An erosion model to predict soil loss specific for rangeland applications is needed because existing erosion models were developed from croplands. Hydrologic and erosion processes are different on rangelands than croplands due to much higher levels of heterogeneity in soil and plant properties and the consolidated nature of the soils. The purpose of this Handbook is to improve the understanding of hydrologic processes and sources and transport mechanisms of sediment in rangeland catchments at the scale of the hillslope. The first Handbook, Part 646 Rangeland Hydrology and Soil Erosion Processes, provides a review of relevant rangeland hydrology literature on what is known about the impact of range management practices and field experiments conducted across the western United States. This Handbook, Part 647–The RHEM Guide, provides the background for understanding how to use the Rangeland Hydrology and Erosion Model (RHEM) and understand its output for making informed decisions before implementing new management actions. The RHEM model is a newly conceptualized, process-based erosion prediction tool specific for rangeland application, based on fundamentals of infiltration, hydrology, plant science, hydraulics, and erosion mechanics. The model is event-based and was developed specifically from rangeland data. The erosion prediction tool estimates runoff, erosion, and sediment delivery rates and volumes at the spatial scale of the hillslope and the temporal scale of a single rainfall event. The data drawn on to develop and validate the RHEM series of tools contains over 2,000 rainfall simulation plots and 100 plant communities collected over the last 40 years across the western United States by the Agricultural Research Service and the Natural Resources Conservation Service. These data can be used to understand ecological processes when combined with the RHEM tools to provide sound science when making critical land management decisions. The RHEM assessment tool provides information that can be combined with state and transition models and enhance Ecological Site Descriptions. The RHEM assessment tool has been incorporated into the Automated Geospatial Watershed Assessment (AGWA) tool for understanding and predicting hydrologic and soil erosion processes at the watershed scale.

Technical Abstract: Soil loss rates on rangelands are considered one of the few quantitative indicators for assessing rangeland health and conservation practice effectiveness. An erosion model to predict soil loss specific for rangeland applications is needed because existing erosion models were developed from croplands. Hydrologic and erosion processes are different on rangelands than croplands due to much higher levels of heterogeneity in soil and plant properties and the consolidated nature of the soils. The purpose of this Handbook is to improve the understanding of hydrologic processes and sources and transport mechanisms of sediment in rangeland catchments at the scale of the hillslope. The first Handbook, Part 646 Rangeland Hydrology and Soil Erosion Processes, provides a review of relevant rangeland hydrology literature on what is known about the impact of range management practices and field experiments conducted across the western United States. This Handbook, Part 647–The RHEM Guide, provides the background for understanding how to use the Rangeland Hydrology and Erosion Model (RHEM) and understand its output for making informed decisions before implementing new management actions. The RHEM model is a newly conceptualized, process-based erosion prediction tool specific for rangeland application, based on fundamentals of infiltration, hydrology, plant science, hydraulics, and erosion mechanics. The model is event-based and was developed specifically from rangeland data. The erosion prediction tool estimates runoff, erosion, and sediment delivery rates and volumes at the spatial scale of the hillslope and the temporal scale of a single rainfall event. The data drawn on to develop and validate the RHEM series of tools contains over 2,000 rainfall simulation plots and 100 plant communities collected over the last 40 years across the western United States by the Agricultural Research Service and the Natural Resources Conservation Service. These data can be used to understand ecological processes when combined with the RHEM tools to provide sound science when making critical land management decisions. The RHEM assessment tool provides information that can be combined with state and transition models and enhance Ecological Site Descriptions. The RHEM assessment tool has been incorporated into the Automated Geospatial Watershed Assessment (AGWA) tool for understanding and predicting hydrologic and soil erosion processes at the watershed scale.