Maps, Graphs, and Data

Hurricane Harvey's Effect on Soil Moisture

Symbol map of Hurricane Harvey's effect on soil moisture around Houston Texas.

Hurricane Harvey dropped record-breaking amounts of rainfall, particularly around Houston, Texas on August 25, 2017. Have your students analyze the legend below and this proportional symbol map of Hurricane Harvey to answer the questions below.  Note:  Soil moisture is expressed in volumetric terms, water by volume/volume of soil.

Scale for Map


Harvey Map


Mini Lesson

Student Activity Sheet
  1. What does the size of the dot represent? The rate of change in the amount of moisture in the soil

  2. What does the color represent? The quantity of moisture per cm cubed per cm cubed

  3. What area was the most impacted by Hurricane Harvey? How do you know? North West of Houston because it has the largest and darkest hexagons.

  4. Why do you think there was not a change in soil moisture in the city of Houston? The surface of a city is mainly impermeable so the water isn’t able to soak into the soil but rather runs off into its watershed

  5. What is one question you have when looking at this map? Answers can vary but examples are; why did the East side of Houston not have as drastic soil moisture change compared to the west side of the city; what was the path the storm took; how much water dumped onto the city?