1a. Objectives (from AD-416):
The long-term objective of this project is to develop soil and water conservation decision support information for policy makers, land managers, and producers to help identify the scope of additional conservation measures to mitigate the detrimental impacts of anticipated climate change. The Fort Cobb Reservoir watershed in west central Oklahoma is representative of the physiography of the region and was selected as the project watershed. Obj 1: Quantify the effects of past climate variations on runoff, soil erosion, sediment transport and fate, and nutrient movement for the Fort Cobb Reservoir (FCR) watershed, using available data records, reconstructed chronology of reservoir sedimentation, and computer modeling of watershed processes. 1A: Identify past climate variations; determine corresponding impacts on watershed runoff, sediment yield, and reservoir sedimentation; derive climate-flow-sediment relationships. 1B: Reconstruct chronology of watershed sediment yield from reservoir sedimentation profiles; identify sediment sources; estimate sediment yield of major erosive storm-runoff events for calibration/validation of simulation models. 1C: Identify reference land use, conservation, and climate conditions to serve as baseline for assessment of climate change scenario impacts; calibrate/validate hydrologic and erosion simulation models using data developed under subobj 1A/1B. Obj 2: Determine the potential impacts of three selected climate change scenarios on the hydrologic system and on the soil and water resources of the FCR watershed. 2A: Determine trends in annual precipitation and air temperature for 3 greenhouse gas (GHG) emission scenarios; identify changes in seasonal/monthly precipitation and temperature distribution within a year, 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 ensembles of daily weather outcomes for each GHG emission scenario that reflect the statistical characteristics of projected climate change for use in climate impact assessment in Obj 3. Obj 3: Identify soil and water conservation strategies and options that are adapted to and mitigate the detrimental impacts of climate change, and test their effectiveness at enhancing the resilience of agricultural landscapes under anticipated climatic changes. 3A: Estimate extent of soil erosion/sedimentation under 3 selected GHG emission scenarios assuming constant baseline land use and conservation conditions; identify soil conservation options/practices/coverage that mitigate soil erosion and sedimentation directly attributable to climate change; determine risk of exceeding soil erosion and sedimentation rates under climate change. 3B: Develop communication tools that synthesize information across combinations of conservation practices, conservation coverage, climate change scenario, and conservation effectiveness and help land managers select conservation options that best meet soil/water conservation goals.
1b. Approach (from AD-416):
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.
3. Progress Report:
Completed building the soil and water assessment tool (SWAT) model project for the Fort Cobb Reservoir experimental watershed (FCREW) and also completed climate and flow data acquisition and quality control. Initial SWAT calibration and validation for hydrology was also completed. About 80 samples of surface soils, channel bed sediment, and stream/gully bank materials were sampled in the Bull Creek watershed. The surface soil samples were stratified based on soil type and land uses, and the channel bed sediment samples were taken across all the stream orders. Gully and stream bank samples were also taken at locations where erosion is currently active to represent subsoil sediment sources. Apart from soil samples, about 40 runoff sediment samples were collected at about 10 sites across the watershed using sediment traps. In addition, about 10 sediment cores were taken from the reservoir that controls the entire Bull Creek watershed. All 80 surface samples and 40 runoff sediment samples were evaluated by chemical element analysis for potential identification of sediment source tracers or fingerprints. In addition, about 50 soil samples from 9 transects in a rangeland sub-watershed were collected for Cesium analysis to characterize soil redistribution in the area. The samples were shipped to Beijing Normal University for gamma spectrometer analysis under a cooperative research agreement. A weather-generator-based, statistical spatiotemporal downscaling method developed by Grazinglands Research Lab scientists was evaluated against measured station precipitation at five Oklahoma stations (Hooker, Weatherford, Lahoma, Chandler, and Idabel), with annual precipitation ranging from 400 to 1200 mm. The downscaling method was also evaluated using station precipitation data from UK, Australia, Canada, Brazil, and US under various climatic zones ranging from polar to tropical. For each station, a dry period and a wet period were selected. The dry period was assumed the present climate and the wet period the future climate. The method was calibrated to the dry period, and input parameters of the weather generator were adjusted based on the monthly precipitation changes between the two periods. The adjusted parameters were used to generate daily precipitation series for the wet period. Overall results showed that the downscaling method is capable of generating daily precipitation series that possess desirable characteristics of daily precipitation amounts, frequency, and durations of dry and wet spells in different climatic zones, especially for future climate experiencing non-stationary variation or change.
1. New downscaling methodology enables generating daily precipitation for climate change scenarios. Climate change scenarios produced by the National Oceanic and Atmospheric Administration are at a spatial and temporal scale that is too large for direct application for investigations of soil, water and agricultural production issues. This significantly limited our capabilities to model the impacts of climate change scenarios in agricultural landscapes and watersheds. A methodology was needed to bridge the gap between the time and space scales at which the climate change scenarios are delivered and the daily weather data needed for farm or watershed scale applications. Such a methodology was developed and verified with precipitation data from various continents and included climatic zones that ranged from polar to tropical. The methodology has been published and is being used in climate change impact applications.
Andrews, W.J., Becher, C.J., Steiner, J.L., Daniel, J.A., Garbrecht, J.D. 2011. Synopsis of integrated science to support the assessment of conservation practices in the Fort Cobb reservoir watershed, southwestern Oklahoma. In: Becher, C.J. (ed.). Assessment of Conservation Practices in the Fort Cobb Reservoir Watershed, Southwestern Oklahoma. USGS - Scientific Investigations Report. Available: http://pubs.usgs.gov/sir/2010/5257/.