Towards a better understanding of the evaporative cooling of rivers: case study for the Little Southwest Miramichi River (New Brunswick, Canada)

Abstract Stream temperature plays an important role in many biotic and abiotic processes, as it influences many physical, chemical, and biological properties in rivers. As such, a good understanding of the thermal regime of rivers is essential for effective fisheries management and the protection of aquatic habitats. Moreover, a thorough understanding of underlying physical processes and river heat fluxes is essential in developing better and more adaptive water temperature models. Very few studies have quantified river evaporation and rivers’ corresponding evaporative cooling component. The present study investigated the evaporative cooling of the Little Southwest Miramichi River in Eastern Canada by calculating the evaporative heat flux and overall heat fluxes using in-situ data. Results showed that the evaporative heat flux reached −300 W m−2 mid-day when high water temperatures were observed. The daily evaporative heat flux can thus account for close to 50% of the total heat losses, followed by longwave radiation (25%), streambed heat fluxes (20%), and sensible heat (5%). Our results show that the evaporative heat flux can be a critical cooling mechanism for wide and shallow rivers during high summer temperatures.