Hotter air results from the hot concrete. Then the air has more capacity for holding water instead of precipitating it out as clouds or rain. This increases the

Hotter air results from the hot concrete. Then the air has more capacity for holding water instead of precipitating it out as clouds or rain. This increases the likelihood of 100%RH conditions, in direct sunlight, on top of a huge thermal mass heated to way above body temps, making heat waves deadlier because evaporative cooling becomes moot at that humidity and you're essentially in desert conditions surrounded by hot rocks.