Development of a Global River Water Temperature Model Considering Fluvial Dynamics and Seasonal Freeze-Thaw Cycle

Abstract

In this study, we developed a global river water temperature model that explicitly represents water and heat budgets. The model considers fluvial dynamics such as floodplain inundation and as well simulates seasonal freeze‐thaw cycles for temperate and arctic rivers, and it was found that proposed physically based parameterizations appropriately reproduced in situ observed seasonal variations in 12 global rivers. Theoretically, floodplain inundation has two major effects on water temperature variability: (1) “broadening” of water surfaces, which increases heat exchange with the atmosphere and friction with river bed, and (2) “shallowing” mean water depth, which increases the absorption rate of shortwave radiation per unit volume. In contrast to the broadening which affects both warming and cooling processes, the shallowing causes warming only and has dominant impacts mainly during the ice melting season in Arctic regions and the rainy season in the tropics. Furthermore, it was revealed that lateral mixing between channel and floodplain has a significant impact on determination of river water temperature. Although water temperature plays an important role in water quality and riverine material circulation linking terrestrial and coastal environments, it has not been considered in most Earth system models. The improvements in global‐scale river water temperature modeling demonstrated in this study will benefit for future Earth systems research.