Dynamic SPARROW model application data for seasonal total nitrogen and total phosphorus loads in streams across the conterminous United States, 2000 through 2020

This model application data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading in streams across the conterminous United States (263,494 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (SPAtially Referenced Regressions On Watershed attributes) model. All model files are provided to reproduce the output predictions interpreted by Miller and others (2026), including the input and calibration data, model control files, and model source code (see ReadMe_conus.txt). There were 2,424 TN and 2,803 TP stations used to calibrate the models. For convenience, the seasonal load predictions were further summarized at coarser-spatial-scale 12-digit-hydrologic-unit-code watersheds (77,220). Additional weather-normalized load prediction scenarios are provided to support trend analyses. The modeled period was from December 1999 through November 2020 in seasonal timesteps, or 84 periods, and the following seasonal definitions were applied: winter includes December, January, and February; spring includes March, April, and May; summer includes June, July, and August; and fall includes September, October, and November.