A heat wave is different depending on its location. According to the World Meteorological Organization, a region is in a heat wave if it has more than five consecutive days of temperatures that are more than 9°F (5°C) above average.
A high pressure cell sitting over a region with no movement is the likely cause of a heat wave.
Droughts also depend on what is normal for a region. When a region gets significantly less precipitation than normal for an extended period of time, it is in drought. The Southern United States is experiencing an ongoing and prolonged drought.
It’s hard to define a heat wave or a drought because these phenomena depend are deviations from normal conditions in a region.
A heat wave is caused when a warm high-pressure cell sits over a region.
Drought may have extremely severe consequences depending on its duration and intensity.