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Heat Waves and Droughts

Heat waves and droughts are more extreme versions of normal weather; a heat wave occurs when a warm high pressure sits over a region.

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California Drought

California Drought

These two images were taken on January 18. That date in 2013 was a dry year, but that’s the image with the snow. January 18, 2014 depicts the same region with virtually no snow, the driest January on record.

News You Can Use

  • The 2013 image shows snow in the Sierra Nevada and into the state of Nevada, with a bit in the northern Coast Range. The large lake in the Sierra Nevada is Lake Tahoe.
  • The 2013 image also has greener trees in the Coast Range and greener fields in the Central Valley, where much of our food is grown.
  • The Tuolumne River basin is the water source for 2.6 million residents in the San Francisco Bay Area.
  • The Pacific Decadal Oscillation occurs north of the equator, unlike ENSO, which occurs right around the equator.

Can You Apply It?

With the links below, learn more about the California drought. Then answer the following questions.

  • ScienceAtNASA, ScienceCasts, California Drought (video):


  1. What are instruments being flown above the Sierra snowpack measuring? What will these measurements be used to calculate?
  2. What is the Pacific Decadal Oscillation? How could the PDO cause the drought?
  3. How could the drought end suddenly?
  4. What is the evidence that this drought is caused or exacerbated by climate change?
  5. What is the evidence that this drought is not caused or exacerbated by climate change?
  6. How could the drought be caused both by natural variability and climate change?

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