Antecedent soil moisture is an important factor in the generation of runoff, but guidance for modeling moisture conditions in semiarid catchments is limited and conflicting. In this study, the impact of antecedent moisture was assessed at the plot scale (2.8 m²) using a portable rainfall simulator, and at the catchment scale based on observed precipitation and discharge for a 2.8 km² watershed in central New Mexico. Performance of three loss models commonly used for hydrologic analysis in the southwestern U.S. was tested at both scales. High initial moisture content led to substantially higher runoff ratios at both scales, confirming the importance of antecedent soil moisture for runoff predictions in semiarid drainages. Hydrologic parameters estimated based on plot experiments, however, were highly variable and cannot easily be upscaled to the catchment scale. Loss model performance was clearly scale dependent: more simplistic (one- and two parameter) loss methods out-performed a more complex (four parameter) model at the watershed scale, while the opposite held true for test plot simulations. At the catchment scale, all models performed poorly for small runoff events, but yielded acceptable results for storms causing large discharges if antecedent soil moisture was considered. Failing to account for antecedent moisture led to simulated runoff volume errors up to one order of magnitude.

This dataset includes 19 runoff and infiltration time series measured at ten test plots in central New Mexico. Tests were conducted using a portable rainfall simulator. A nozzle, suspended 3 m above ground, was used to spray water onto a 2.8 m² test plot at a constant rate of 55.9 mm/h. Below the nozzle, a sheet metal border was driven into the ground to a depth of approximately 5 cm. Any runoff originating inside the test plot was directed to a graduated container. Using a time lapse camera, runoff volume was recorded in 2-minute increments. For each time step, runoff rate was determined by dividing the incremental runoff volume by the plot size. Infiltration rate for each time step was calculated by subtracting the runoff rate from the rainfall rate. Each plot was tested twice – first under dry soil conditions, and a second time after approximately 2-3 days (wet conditions). At each site, one soil sample was subjected to particle size analysis. Before each test run, moisture content of the top 15 cm of the soil profile was determined from a core sample by drying.