 A heat wave is a period of abnormally hot weather. While heat waves aren't as dramatic as most severe storms, they're just as dangerous. Heat waves can be hazardous to your health. They can also trigger massively destructive wildfires that pollute the air. Heat waves are often more intense in cities where asphalt and concrete absorb rather than reflect heat. Their frequency and intensity of heat waves are increasing as Earth's climate gets warmer. During a heat wave, stay cool, drink lots of water, and reduce physical activity. And check on family, neighbors, and pets who may be at risk.