Modeling Hydrologic Influence of Agricultural Management Using the National Water Model

About 20% of the contiguous United States (CONUS) is croplands. The seasonal crop growth and related water management practices such as irrigation and tile drainage considerably affect the water fluxes at local and regional scales. To improve the representation of agriculture management processes in the National Water Model (NWM), we implemented crop-growth, irrigation, and tile-drainage modules into NWM. Accompanying these new modeling modules, we incorporate the following agriculture management data sets: spatial maps of crop types, planting/harvest dates, growing degree days, in-situ and satellite-derived irrigation fraction, and tile-drain fraction for the CONUS. As the first step to assess its impact, the NWM with the above-mentioned additions was executed for several selected watersheds located in regions with heavy usage of irrigation and tile drainage, including the Iowa River (Iowa), Winnebago River (Iowa), South Loup River (Nebraska), Bazile Creek (Nebraska), and Sugar Creek (Illinois) watersheds. Observed streamflow from year 2010 to 2018 time period were used to evaluate NWM. Estimates from the reference (or operational) NWM were also used to evaluate the performance of this updated NWM. We will discuss the individual and combined effects of crop-growth, irrigation, and tile drainage on the evolution of streamflow during spring and summer seasons.