Technical Abstract: Multiyear precipitation variations in long climatic records are believed to have a considerable impact on watershed runoff, soil erosion, sediment yield, and reservoir sedimentation. A study was conducted on the Fort Cobb reservoir watershed in central Oklahoma to quantify the impact of multiyear wet and dry periods on watershed runoff and sediment yield. Findings showed that wet or dry periods amplified into comparatively larger watershed runoff and sediment yield variations. For the case at hand, a mean annual precipitation difference between wet and dry periods of 33% led to a 100% difference in runoff, which in turn led to a 183% difference in sediment yield. It follows that assessment of effectiveness and benefits of many soil conservation practices is best performed under wet period conditions, as these are conditions for which conservation practices are intended to apply. On the other hand, assessment of long term reservoir sedimentation ought to be based on a representative mix of wet and dry periods, because reservoir sedimentation is the result of a continuous and cumulative process. Also, computer simulated soil and water conservation impacts depend on the climatic data used in model calibration, validation, and application, and simulation results should be qualified in terms of any wet and dry periods underlying the various simulations. Thus, this study leads to conclude that the suitability of a climatic record for watershed runoff, sediment yield, and soil and water conservation assessments should be determined, and findings interpreted, in terms of multiyear wet or dry periods that may dominate the climatic record.