RNSTM: A Network‐Link Approach to Streamflow Temperature Modeling

This work presents the development and validation of the River Network Streamflow Temperature Model (RNSTM), which solves the energy balance equations at the air‐water interface within the channels to estimate their temperature. RNSTM considers solar radiation, net longwave radiation, evaporative heat flux, and convective heat transfer. Additionally, it includes sub‐surface heat transfer and the rainfall effects on water temperature. First, we present the formulation and testing of a lumped‐energy balance model. For this test, we used atmospheric forcings from ground‐based observations and the High‐Resolution Rapid Refresh (HRRR) weather forecasting system. Next, we formulated RNSTM for a general river network using the ordinary differential equations (ODE) solver that is part of the Hillslope Link Model (HLM). We tested RNSTM using HRRR meteorological data and discharge simulations from HLM and we validated it using United States Geological Survey (USGS) water temperature observations at the Cedar River at Waverly, Iowa, for 2021. Our model results show potential for large‐scale deployment and water quality‐related applications.