One of the more immediate expressions of climate change is increased frequency and intensity of extreme heat events. Extreme heat impacts can be particularly large in cities due to preexisting urban heat island effect and high concentration of people. These impacts include heat-related mortality and morbidity, strain on energy infrastructure, degraded air quality, and reduced mental health and worker productivity, which raise an urgent need for a better understanding of the processes that contribute to dynamics of extreme heat risk in cities.

Cities consume 78% of the world's energy. It is theoretically impossible to eliminate anthropogenic heat (AH) from energy consumption. Anthropogenic heat affects local climate in urban areas, contributing to phenomena such as heat islands. In this presentation, we discuss interactions between anthropogenic heating and urban micro-climate dynamics, under extreme heat conditions.

We use Los Angeles metropolitan area as a testbed where we employ a suite of satellite-supported, high-resolution (500 m) regional climate simulations coupled with an urban canopy model (UCM) to reproduce urban micro-climate during a prolonged extreme heat condition in August-September, 2009. Unlike the majority of previous studies that rely on data from energy statistics, we use detailed Building Energy Modeling (BEM), using Energy Plus (E+), and building informatics to estimate anthropogenic heating from buildings and their response to changes in urban micro-climate under extreme heat condition. Here, we uniquely distinguish between two major components of anthropogenic heating from buildings: AH from 1) HVAC heat rejection and 2) building exhaust/relief air. We show that HVAC heat rejection increases significantly during extreme heat conditions; AH from building exhaust/relief air, however, is decreased as the outdoor air temperature rises. We show that AH contributes to UHI, particularly during the night, and has a significant impact on daytime boundary layer height. We further discuss dynamics of the feedback process between AH and urban micro-climate under extreme heat conditions and how climate change may change these dynamics in the future.