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Impact of weather and climate scenarios on conservation assessment outcomes

J. D. Garbrecht, M. A. Nearing, F. Douglas Shields, M. D. Tomer, E. J. Sadler, J. V. Bonta, C. Baffaut
Journal of soil and water conservation 2014 v.69 no.5 pp. 374-392
Conservation Effects Assessment Project, agricultural management, agricultural watersheds, bank erosion, climate, climate change, conservation practices, energy, funding, planning, plant cultural practices, rain, rangelands, rivers, runoff, sediment transport, sediment yield, sediments, soil, soil conservation, streams, watershed hydrology, Arizona, Iowa, Mississippi, Missouri, Oklahoma
Selected watershed studies of the Conservation Effects Assessment Project (CEAP) are reviewed and findings are interpreted from the perspective of potential conservation outcomes due to climate change scenarios. Primary foci are runoff, soil erosion, sediment transport, and watershed sediment yield. Highlights, successes, and challenges with regards to climate change impacts on soil erosion, runoff, and watershed sediment yield are presented. The covered information adds to the existing knowledge base of climate change impacts and provides another piece of information that may be useful in the planning and management of agricultural watersheds; assessment of conservation needs; and development, funding, and implementation of conservation programs. The selected conservation assessment studies include, among others, a thought experiment on the sensitivity of soil erosion, runoff, and sediment yield to changes in rainfall; a computer-based investigation of potential climate change effects on runoff and soil erosion in a southeastern Arizona rangeland; the complex response of northern Mississippi watersheds to runoff variations and channel stabilization measures; the impact of conservation practices and a persistent pluvial period on watershed runoff and sediment yield in Oklahoma; and stream bank erosion during major flooding in Iowa and river corridor management. A study of rainfall-runoff in an north-central Missouri watershed and a curve number analysis in a northern Appalachian experimental watershed are included herein. Findings showed that climate change scenarios of increased precipitation intensity lead to an exponential increase in soil erosion, runoff, and watershed sediment yield, thereby stressing current conservation practices or future practices designed with present day practice standards. This diminishes conservation practice effectiveness and increases sediment supply to the stream network. The sensitive response of the watershed hydrologic system may lead to renewed soil erosion that is large enough to offset the reduction in soil loss achieved by current conservation practices. However, in alluvial-floodplain environments with non-cohesive bed and bank material, watershed sediment yield is controlled by channel discharge and energy slope, neither of which is influenced by traditional in-field conservation practices or channel bank stabilization structures. Thus, control of sediment yield will gradually shift in the downstream direction from sediment supply to sediment transport capacity and blur any existing relation between a climate change signal, in-field conservation outcomes, and sediment yield at watershed outlets. Targeting conservation practices to erosion prone areas, expanding conservation coverage, and adapting agronomic practices may be necessary to prevent excessive soil erosion and downstream sedimentation under climate change scenarios that include intensified precipitation.