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 -4oC) 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.