Impacts of urbanization on summer precipitation and management of engineering infrastructure systems for Montreal

Despite extensive efforts in the past few decades, it still remains a big challenge to reach a coherent and concrete conclusion on how urbanization modifies precipitation for differently located and configured cities. To investigate the impacts of urbanization on summer precipitation characteristics over Montreal, the second most populous city in Canada, two sets of high-resolution numerical simulations using the Global Environmental Multiscale (GEM) model, for consecutive summers (2015-2019), one with detailed urban representation using the Town Energy Balance (TEB) model and one without TEB, are used in this study.

To validate the performance of GEM, the simulation results are directly compared with observations from Environment and Climate Change Canada weather stations, spread across the city. Results show that GEM is able to capture the general climate characteristics such as diurnal cycles of 2-meter air temperature, relative humidity, 10-meter wind pattern, and precipitation intensity distribution reasonably well over Montreal. Comparison of the two sets of simulations shows that urbanization induces a general reduction of the total summer precipitation amount over Montreal due to decreased evapotranspiration caused by land surface modification. Results also suggest an increasing tendency of extreme precipitation amount at higher temperatures in the simulations with TEB, catalyzed by enhanced surface convergence and moisture supply. Additional sensitivity experiments helped understand how urbanization has impacted the management of various engineering systems, such as road infrastructure.