The long-term objective is to develop soil and water conservation decision support information for policy makers, land managers, and producers to identify conservation measures to mitigate the impacts of climate change. The Fort Cobb Reservoir(FCR)watershed, Oklahoma, was selected as the project watershed. Obj 1: Quantify the effects of past climate variations on runoff, soil erosion, sediment transport and nutrient movement for the FCR watershed, using available data records, reconstructed chronology of reservoir sedimentation, and computer modeling. 1A: Identify past climate variations and determine impacts on watershed runoff, sediment yield, and reservoir sedimentation. 1B: Reconstruct chronology of watershed sediment yield from reservoir sedimentation profiles; identify sediment sources; estimate sediment yield of major erosive storm-runoff events. 1C: Identify baseline land use, conservation, and climate conditions for impact assessment of climate change scenarios; calibrate/validate hydrologic and erosion models. Obj 2: Determine the potential impacts of 3 selected climate change scenarios on the hydrologic system and soil and water resources of the FCR watershed. 2A: Determine trends in annual precipitation and temperature for 3 greenhouse gas (GHG) emission scenarios; identify changes in seasonal precipitation and temperature distribution, estimate monthly precipitation and temperature statistics expected to prevail around the half century mark. 2B: Develop/evaluate spatio-temporal downscaling methods that integrate changed climate statistics into a synthetic weather generator; generate daily weather outcomes for each GHG emission scenario that reflect the statistical characteristics of projected climate change. Obj 3: Identify soil and water conservation strategies and options that are adapted to and mitigate the impacts of climate change, and test their effectiveness at enhancing the resilience of agricultural landscapes under climatic changes. 3A: Estimate extent of soil erosion/sedimentation under 3 GHG emission scenarios; identify soil conservation options/practices/coverage that mitigate soil erosion and sedimentation attributable to climate change; determine risk of exceeding current soil erosion and sedimentation rates. 3B: Develop communication tools that synthesize information across combinations of conservation practices, conservation coverage, climate change scenario, and conservation effectiveness. Obj 4: Develop science-based, region-specific information and technologies for agricultural and natural resource managers that enable climate-smart decision-making and where possible provide assistance to enable land managers to implement those decisions. The work will be conducted at the USDA Southern Plains Climate Change Hub and will be coordinated with NRCS, FS, and other USDA and non-USDA organizations in accordance with guidance found in the USDA Climate Change Hubs Charter and Terms of Reference.
The effects of past climate variations on runoff, soil erosion, sediment transport and fate, and nutrient movement for the Fort Cobb Reservoir (FCR) watershed are quantified based on available climate, hydrology, and environmental data records, reconstructed chronology of reservoir sedimentation, and computer modeling of watershed processes. Published climate data from Global Climate Models (GCM) are used to determine trends in annual precipitation and air temperature for three greenhouse gas (GHG) emission scenarios, identify changes in seasonal and monthly precipitation and temperature distribution within a year, and estimate monthly precipitation and temperature statistics that are expected to prevail around the half century mark. Synthetic weather generation models are used to generate daily weather outcomes that reflect the statistical characteristics of the projected climate change. Soil and water conservation strategies and options that are adapted to and mitigate the detrimental impacts of climate change are identified based on simulated soil erosion and sedimentation. Selected soil conservation options, practices, and coverage are tested with regard to their effectiveness at enhancing the resilience of agricultural landscapes under anticipated climatic changes. Risk of exceeding predefined soil erosion and sedimentation rates under climate change are determined. Information across combinations of conservation practices, conservation coverage, climate change scenario, and conservation effectiveness is synthesized and communicated in a format relevant to land managers, conservationists, and producers, as well as other practitioners. Climate smart agricultural management and decision making potential is determined based on the latest available climate information of long term historical climate records, the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and climate projections of Global Circulation Models (GCM). Based on the insight gained, a demonstration crop production application is developed to illustrate producer's benefits and risks of including climate variations and change as an agricultural management criterion. The effects and implications of GCM climate projection lead time and uncertainties on the climate-based decision making in agricultural production and natural resources conservation is made clear.
Soil redistribution and sediment source identification: Hundreds of soil and sediment samples were collected from the Bull Creek watershed. Samples were analyzed for 30 chemical elements and radionuclide Cesium (137Cs). Three 137Cs conversion models were used to convert measured 137Cs inventory along hillslope transects to soil erosion or deposition rates. The 137Cs-estimated soil redistribution rates on hillslopes were compared to soil erosion rates predicted by the Water Erosion Predict Project (WEPP) model, and reasonable agreement was obtained. For sediment source identification, a statistical test and an algorithm were used to select potential tracers from all chemical elements measured. Preliminary results indicated that proportional contributions from upland vs. gully varied with stream orders and drainage areas. Calibration of the Soil and Water Assessment Tool (SWAT) for sediments: Land use, soils, and a digital elevation model for the Fort Cobb Reservoir watershed were used to build the SWAT project. Climate data from four National Weather Service stations were used. The calibrated hydrology model was then calibrated for sediment. Overland, channel, and sediment routing parameters were determined to be sensitive and were therefore included in the calibration. However, results indicated that the basin-wide peak rate adjustment factor for sediment routing in the main channel does not yield satisfactory results. Changes were made that allowed this factor to be calibrated for different reaches of the stream network. This modified code was sent to SWAT developers to incorporate into the ArcSWAT interface. Bi-weekly ARS water quality samples, USGS low-high flow measurements, and total phosphorus data were thoroughly quality controlled and used to develop log-normal water quality-discharge relationships. The relationships were used to generate continuous daily total phosphorous concentrations and loads. Initial activities of the USDA Southern Plains Regional Climate Hub included the establishment of the Hub Steering Committee. The Hub Lead participated in National level Hub telemeetings, creating and submitting reports and documents as required. Monthly coordination telemeetings were established with other federal climate change adaptation programs in the Southern Plains region, including the DOI South Central Climate Science Center, the NOAA Southern Climate Impacts Planning Program, the EPA Region 6 Agricultural Advisor, the NOAA/NESDIS/NWS Southern Region Climate Services Director, the Oklahoma Conservation Commission, and Extension faculty from Kansas State. All critical elements comprising the Climate Hub were initiated. More than 20 presentations relative to the Hub were made to agricultural producers, producer organizations, Tribes, and other state and federal research and service organizations. Climate projections by Global Circulation Models have been downloaded and aligned with the climate in east-central Oklahoma. Weather generator SYNTOR was used to generate synthetic daily precipitation and temperature. Soil erosion and sediment yield from a field planted in winter wheat was calculated using the WEPP model.
1. New insights on soil erosion estimation using radioactive tracers. Fallout radioactive tracers have been widely used to estimate point soil redistribution rates; however, their validity has not been rigorously examined. ARS researchers at El Reno, Oklahoma, synthesized literature and evaluated the tracer technique using sensitivity and uncertainty analyses along with long-term measured soil loss data. The key assumption that the fallout radioactive tracers are spatially uniform is proven false due to the existence of random spatial variations in radioactive travel inventory. The spatial variation is the major uncertainty source of the technique. The technique cannot be used to estimate soil redistribution rate at a particular point as was widely used in the past, due to random nature in radioactive tracer inventory. Nevertheless, it can be used to estimate areal mean soil redistribution rate for a land area as the random component tends to be averaged out. This work presents a new concept for better use of the tracer technique for estimating soil erosion over a landscape.
2. Mitigating the impact of climate change on soil erosion. Precipitation and frequency of extreme events have increased over the last decades and are expected to continue to increase. Special concerns arise in that current soil and water conservation efforts, based largely on climate observations and agronomic practices of the past century, will not keep pace with these climatic changes. Researchers at the USDA, ARS Grazinglands Research Laboratory, El Reno, Oklahoma, investigated options to mitigate impacts of climate change on soil erosion and sediment yield for winter wheat crops in central Oklahoma. A computer simulation investigation revealed that wide implementation of conservation tillage could offset a large portion of the anticipated increase in sediment yield. However, to overcome the large uncertainty in projected climate, more effective conservation measures such as terraces or no-till may be necessary to ensure that future sediment yield from winter wheat fields remains close to today's levels.
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Garbrecht, J.D., Zhang, X.J., Steiner, J.L. 2014. Climate change and observed climate trends in the Fort Cobb experimental watershed. Journal of Environmental Quality. 43:1319-1327.
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