Advancing the realistic simulations of N2O emissions in cold climate watersheds using Soil and Water Assessment Tool

Nitrous Oxide (N₂O) emissions in Soil and Water Assessment Tool (SWAT) is heavily dependent on soil temperature and moisture. However, SWAT has been known to highly under-estimate soil temperature which limits movement of water and nutrients throughout the soil profile and does not replicate freeze-thaw cycles which is of paramount importance in the N₂O emissions. Thus, we integrated modules developed by individual researchers pertaining to energy balanced snow melt, rain-on-snow, energy balanced soil temperature and N₂O emission into a single SWAT model and termed in SWAT Cold Climate N₂O (SWAT-CCN2O). SWAT-CCN2O was then tested for flows, sediments, soil temperature and N2O emission simulation in a representative watershed in Ontario, Canada, the Speed River basin. Compared with the unaltered SWAT model, SWAT-CCN2O was able to significantly capture the pre-spring snowmelt induced flows. A more realistic simulation of soil temperature (soil temperatures did not go below -4^oC) and a satisfactory simulation of sediments and N₂O emissions were observed in the basin, which highlights the potential to use SWAT-CCN2O for streamflow and N₂O simulation in cold climatic catchments. This version of SWAT is made publicly available for further improvements and applications in similar watersheds.