Location: Southwest Watershed Research2011 Annual Report
1a. Objectives (from AD-416)
Objective 1. Provide data bases, knowledge, and information of rangeland erosion at a range of spatial scales for the development, validation, and implementation of erosion decision tools. Objective 2. Develop decision tools including a rangeland specific hydrology and erosion model for the planning and evaluation of sustainable rangeland management.
1b. Approach (from AD-416)
This project addresses the lack of rangeland specific decision tools to quantify the climatic and management effects on the sustainability of rangelands as affected by runoff and erosion. In particular, the Natural Resources Conservation Service (NRCS) and other action agencies have requested a hydrologic and erosion model to contribute to the ecological site description and National Resource Inventory data bases, to assess the efficacy of conservation practices for the Conservation Security Program, and to provide estimates of runoff and erosion for rangeland monitoring and ranch planning. To address this, two objectives were identified: Objective 1. Provide data bases, knowledge, and information on rangeland erosion at a range of spatial scales for the development, validation, and implementation of erosion decision tools and Objective 2. Develop decision tools including a rangeland specific hydrology and erosion model for the planning and evaluation of sustainable rangeland management. Objective 1 consists of three elements on Erosion Processes, one on Conservation Structures, and one on Remote Sensing. The Erosion Processes elements addresses the quantification of the rates and amounts of erosion, sources and sinks of sediment, and biotic and aboitic influences on sediment yield at scales ranging from plot to small watershed. The resulting data and knowledge will be used to validate hydrologic and erosion relationships and for parameter estimation equations for the erosion model. The Conservation Structures element addresses delivering design criteria for local ranchers and provide the erosion model with data on conservation practices. The Remote Sensing element addresses providing parameter estimation for large scale applications of the erosion model and rangeland health assessments. Objective 2 consists of one element on an Erosion Model and one element on an Economic Decision Support System (EDSS). The Erosion Model will be developed for a wide range of erosion related applications, ranging from parameterizing the NRCS ecological site descriptions to ranch planning. The EDSS will be used to calculate the cost benefit ratios of upland conservation management. Formerly 5342-66000-004-00D & 5342-12660-003-00D (4/07).
3. Progress Report
We made progress on both objectives, which fall under NP211. Under Objective 1, a number of advances were made quantifying the effects of climate and climate change on rangeland erosion processes. An analysis of 34 years of precipitation, runoff and sediment data collected from 8 small semi-arid rangeland watersheds in southern Arizona showed that maximum 30 minute precipitation intensity was the primary factor affecting runoff, and runoff was the best predictor for sediment yield, explaining up to 90% of its variability. Drought induced invasion of an exotic African grass, Eragrostis lehmanniana, in a semiarid rangeland in southeast Arizona caused increased runoff and erosion at the hillslope scale but geomorphological features of the watershed alleviated some of the negative effects of vegetation change on net sediment yield. An evaluation of the potential impacts of changes in rainfall characteristics on soil erosion and surface water runoff in southeastern Arizona suggested no significant changes in annual precipitation across the region, but projected mean annual runoff and soil loss approximately doubled due to the increase in the frequency and intensity of extreme rainfall events. An analysis of projected rainfall erosivity changes under climate change in Northeast China suggested changes ranging from 59 to 91%. An evaluation of the impact of low tech erosion check dams showed that wire bound structures yielded higher soil moisture at depth than loose rock structures. A comparison of existing instrumentation for runoff and sediment data collection at the Walnut Gulch Experimental Watershed with an Australian in-channel system for measuring water velocity, depth, turbidity and collecting runoff samples showed that the latter underestimated sediment yield by 16%. Under Objective 2, the development of the Rangeland Hydrology and Erosion Model (RHEM) included new erosion and hydraulic parameters for disturbed conditions in collaboration with ARS Boise. MU contributions to the rangeland portion of the NRCS Conservation Effects Assessment Project resulted in the publication of the new RHEM Rangeland Hydrology and Erosion Model and analysis using RHEM on over 10,000 National Resources Inventory sample locations in the West. We developed a new version of the Facilitator software, (WebFacilitator) that more systematically documents changes in watershed decision making through time and runs both as a standalone program and on the internet. International collaboration included a study with the Istituto di Ricerca per la Protezione Idrogeologica del Consiglio Nazionale delle Ricerche in Perugia Italy on “Climate Change Impacts on Hydrologic and Erosion Function in contrasting Grazing land Environments”. We continued to provide support and training material for the application of a Spanish language version of the Facilitator for watershed planning in collaboration with the ARS sister institution in Mexico, Instituto Nacional de Investigaciones Forestales, Agricolas, y Pecuarias.
1. Rangeland hydrology and erosion model. An erosion model to predict soil loss specific for rangeland applications is needed because existing erosion models were developed for croplands where the hydrologic and erosion processes are different from those found on rangelands. ARS scientists at the Southwest Watershed Research Center published a landmark paper on rangeland soil erosion modeling. The Rangeland Hydrology and Erosion Model (RHEM) was designed to fill that need. RHEM represents erosion processes under disturbed and undisturbed rangeland conditions, it adopts a new splash erosion and thin sheet-flow transport equation developed from rangeland data, and it links the model hydrologic and erosion parameters with rangeland plant communities by providing a new system of parameter estimation equations based on 204 plots in 49 rangeland sites distributed across 16 western U.S. states. RHEM estimates runoff, erosion, and sediment delivery rates and volumes at the hillslope spatial scale and the temporal scale of a single rainfall event. Experiments were conducted to generate independent data for model validation, which indicated the ability of RHEM to provide reasonable runoff and soil loss prediction capabilities for rangeland management and research needs.
2. Runoff and erosional responses to a drought-induced shift in a desert grassland community composition. Historical weather records over the last century show that the number of rainy days and the intensities of rain have been increasing. ARS scientists in Tucson, AZ looked at projected changes in mean annual preciptitation and the power of rainfall to cause erosion during the mid and latter part of this century in Northeastern China using future precipitation predicted from six climate change models uder three green-house gas emissions scenarios (high, medium, and low). Changes were compared to 1960-1999 conditions. Rainfall erosivity increased by 91%,71%, and 59% under the three scenarios suggesting severe detrimental impacts on soil and water resources. The impact of this research will be a better understanding on how climate change will affect soil erosion, as well as point out the need for improved land management practices to improve conservation strategies in a future of non-stationary climate.
3. Long-term runoff and sediment yields from small semiarid watersheds in southern Arizona. Rangeland sustainability is affected by runoff and erosion. ARS scientists from the Southwest Watershed Research Center analyzed 34 years of percipitation, runoff and sediment data collected from 8 small (1.1 to 4.0ha) semi-arid rangeland watersheds in southern Arizona. Average annual preciptitation averaged 400mm with half of the total rainfall occurring from July through September. Runoff depth was about ten percent of annual precipitation depth on average. Ten percent of rainfall events with the largest sediment yields produced over half of the total sediment yield. Maximum 30 minute precipitation intensity was the primary factor affecting runoff and runoff was the best predictor for sediment yield. Fire and drought may have significantly altered the hydrologic sediment response on some of the watersheds, but lack of continuous monitoring of vegetation on the watershed areas complicated interpretation of both fire and grazing management effects.
4. The impact of low-tech erosion control structures. Rangeland restoration strategies rely on adequate soil moisture. ARS researchers in Tucson, Arizona evaluated the impact of low tech erosion control structures for addressing soil and water conservation in rangeland watersheds. Soil moisture impacts were quantified. Significant differences in soil moisture measured through the soil profile on channel banks were found in association with both loose rock and wire bound check dams compared to control sites. Research results quantify this response and will be useful in designing rangeland restoration strategies that rely on soil moisture to improve vegetative cover.
Polyakov, V.O., Nearing, M.A., Stone, J.J., Hamerlynck, E.P., Nichols, M.H., Holifield Collins, C.D., Scott, R.L. 2010. Runoff and erosional response to a drought-induced shift in a desert grassland community composition. Journal of Geophysical Research-Biogeosciences. 115: 1-8. G04027.