Citation: McBean, E.; Bhatti, M.; Singh, A.; Mattern, L.; Murison, L.; Delaney, P. Temperature Modeling, a Key to Assessing Impact on Rivers Due to Urbanization and Climate Change. Water 2022, 14, 1994. https://doi.org/10.3390/w14131994 Academic Editors: Md Jahangir Alam, Monzur A. Imteaz and Abdallah Shanbleh Received: 22 April 2022 Accepted: 17 June 2022 Published: 22 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Temperature Modeling, a Key to Assessing Impact on Rivers Due to Urbanization and Climate Change Edward McBean 1 , Munir Bhatti 1, *, Amanjot Singh 2 , Logan Mattern 1 , Lorna Murison 2 and Patrick Delaney 3 1 School of Engineering, University of Guelph, 50 Stone Rd., Guelph, ON N1G 2W1, Canada; emcbean@uoguelph.ca (E.M.); loganmattern@gmail.com (L.M.) 2 Water and Climate Change Science, Credit Valley Conservation, Mississauga, ON L5N 6R4, Canada; amanjot.singh@cvc.ca (A.S.); lorna.murison@cvc.ca (L.M.) 3 Danish Hydraulic Institute (DHI), Cambridge, ON N3H 3N1, Canada; pad@dhigroup.com * Correspondence: munirabhatti@gmail.com Abstract: With widespread ongoing urbanization and as climate change continues, the importance of protecting the water quality of streams and lakes is intensifying. However, while many water quality constituents in lakes and rivers are of overall interest, water temperature is a ‘key’ variable as temperature influences mixing within a waterbody, influences the acceptability of the habitat for flora and fauna, and serves as a guide to the general health of a stream. To enable the assessment, a physics-based, deterministic hydraulic and heat-balance modeling procedure using the combination of MIKE SHE, MIKE HYDRO and ECO Lab is described to assess heat transfer magnitudes in portions of the Credit River, Ontario. Changes in instream temperature regimes are examined, including both frequency and spatial extent, providing insights into the impacts of urbanization in terms of seasonal temperature shifts arising from land use changes. For flow and temperature regimes, Nash–Sutcliffe model efficiency coefficient (NSE) values of 0.49 and 0.955 were achieved, respectively, for current threshold conditions. Durations of temperature increases from threshold levels indicate that land use changes from current agriculture conditions to urbanization may change stream water temperatures for 9% of the time by 1 ◦ C, and 2% of the time by 2 ◦ C for distances of 1000 m downstream, because of land use change from agriculture to low-density urbanization, and for 20% of the time by 1 ◦ C, and 4% of the time by 2 ◦ C at distances of 1000 m downstream with land use change to high- density urbanization. With climate change RCP 4.5 Scenario in 2050 (Base, for a Wet Year—2017), the continuous amount of time the stream water temperature remains at elevated temperatures of more than 3 ◦ C (from 5000 m to 25,607 m from the most upstream point of Fletchers Creek) for a distance of 20,000 m is more than 13 h. These elevations in temperature may have serious implications for flora and fauna in the creek, particularly impacting the cold-water and mixed-water fish species. Keywords: physics-based hydraulic model; heat balance; land use change; climate change; MIKE SHE and MIKE HYDRO; ECO Lab 1. Introduction With widespread and extensive urbanization, and as climate change continues, the challenges will increase to protect the water quality of ambient lakes and rivers. A fun- damental part of the challenges involves ensuring there is sufficient accuracy implicit in assessing the impacts of urbanization and climate change, meaning there is need for a mathematical model able to assess the degree of change, and the potential merits of various protective actions. However, to ensure that such needs are correctly responded to, there is a key need to ensure the capability of a model is sufficiently robust to accurately assess the impacts. While many water quality constituents in lakes and rivers are of overall interest, water temperature is a ‘key’ variable as temperature influences mixing within a waterbody, Water 2022, 14, 1994. https://doi.org/10.3390/w14131994 https://www.mdpi.com/journal/water