Climate change projections suggest that, over the next few decades, extreme heat events will become more frequent and their impacts can be especially large in cities due to a high concentration of people and preexisting urban heat islands (UHIs).  Here we use California as a testbed where we employ a suite of high-resolution future regional climate simulations coupled with a satellite-driven urban canopy model and a spatially explicit population projection to investigate the interacting effects of climate change, population growth, and urban heat mitigation measures, such as cool roofs, on exposure to extreme heat events. We find that climate change and population growth reinforce one another to drive substantial increases in future exposure to heat extremes and associated energy demands for cooling buildings.  We further find that heat mitigation measure such as widespread adoption of cool roofs can substantially reduce these impacts in urban areas.