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9.28: Heat Waves and Droughts

Difficulty Level: At Grade Created by: CK-12
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Why are these children playing in a fire hydrant?

The deadliest weather phenomena are not blizzards or hurricanes but heat waves. People who live in areas where the weather is usually not hot may not have air conditioning. Children have a way of finding a solution to a problem that usually involves fun.

Heat Waves

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.

Heat waves have increased in frequency and duration in recent years. The summer 2011 North American heat wave brought record temperatures across the Midwestern and Eastern United States. Many states and localities broke records for temperatures and for most days above 100°F.


A high pressure cell sitting over a region with no movement is the likely cause of a heat wave.

What do you think caused the heat wave in the image below (Figure below)? A high pressure zone kept the jet stream further north than normal for August.

Satellite image of a heat wave

A heat wave over the United States as indicated by heat radiated from the ground. The bright yellow areas are the hottest and the blue and white are coolest.


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.

Drought has many consequences. When soil loses moisture it may blow away, as happened during the Dust Bowl in the United States in the 1930s. Forests may be lost, dust storms may become common, and wildlife are disturbed. Wildfires become much more common during times of 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.

Explore More

Use these resources to answer the questions that follow.


  1. What is the difference between record breaking heat waves in the past and now?
  2. Between 2000 and 2009 in the U.S., how did heat waves stack up against cold events?
  3. What evidence is indisputable?
  4. How does Professor Demming figure out what the cause of the heat is?
  5. When was carbon dioxide last as high in the atmosphere?
  6. Where does the carbon dioxide come from?
  7. Why does carbon dioxide increase Earth's temperature?
  8. How much warmer has the world gotten in the past 140 years?


  1. How is a heat wave defined?
  2. How is a drought defined?
  3. How does the position of the jet stream cause a heat wave?




A long period of lower than normal rainfall for a particular region.
heat wave

heat wave

A period of prolonged excessively hot weather for a particular region.

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Difficulty Level:

At Grade


Date Created:

Feb 24, 2012

Last Modified:

Jan 30, 2016
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