Long-Term Spatio-Temporal Variation in Runoff Curve Number under Consistent Cover Conditions: a Southeastern US Case Study

Runoff, erosion and pollutant transport are influenced by spatial and temporal variation in soil hydraulic properties. Hydrologic models contain parameters that are related to these properties. Model parameters can be anticipated to exhibit similar variation which, when characterized, can improve runoff estimates. This study used plot-scale data from a 0.07 ha grassed study area in the southeastern US to characterize spatio-temporal variation in the NRCS curve number (CN) parameter. Based on over 200 rainfall-runoff data pairs collected over a 19-year period, CN exhibited highly variable (coefficient of variation up to 0.54) spatial behavior. Within-plot variation also demonstrated discernible spatial structure, with high variation associated with low CN. While preserving some similarities, spatial structure of CN and connectedness of regions of similar CN varied with runoff event date. Temporal trends were detected, with some regions demonstrating increasing trends and others decreasing. Rainfall-runoff plot characteristics and experimental protocols were consistent during the period of data collection; based on spatial distribution of CN values and trends as well as observation, traffic patterns and mammalian bioturbation are hypothesized as major sources of observed spatio-temporal CN variation.