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MapMaker: Drought Index

MapMaker: Drought Index

A drought is a natural hazard and a normal part of climate variability characterized by an extended period of dryness or a deficiency or lack of precipitation. Use MapMaker to explore this event with the Global Precipitation Climatology Centre Drought Index.

Grades

5 - 12+

Subjects

Conservation, Earth Science, Climatology, Meteorology, Geography, Geographic Information Systems (GIS), Human Geography, Physical Geography

Image

Global Drought Index

National Geographic

A drought is a natural hazard that is characterized by an extended period of dryness or a deficiency or lack of precipitation. Droughts are normal for many climate zones and are a natural part of climate variability. They may last for weeks, months, or even years. There are four types of drought.

  1. An agricultural drought occurs when there is not enough soil moisture to grow crops. This can be due to a lack of precipitation or reduced groundwater or reservoir levels needed to maintain irrigation.
  2. A hydrological drought occurs when surface or groundwater levels decrease. This could be due to reduced precipitation totals or overuse.
  3. A meteorological drought occurs when a place receives less precipitation than normal.
  4. A socioeconomic drought occurs when the demand for a good exceeds the supply due to a weather-related deficit in water.

Drought has many different, interconnected impacts. One of the most obvious are those influencing the agriculture industry. Without enough water, crops fail which, results in food shortages for humans and livestock. This drives up prices causing some families to go without the goods impacted by the dry spell. While irrigation from surface or groundwater sources may be able to alleviate the issue in the short term, these have their own drawbacks. For example, pumping groundwater at a faster rate than it can be replenished (if it can be replenished) will lead to land subsidence which can damage critical infrastructure or make room for seawater intrusion in coastal regions killing salt intolerant species–including crops–or causing contamination of drinking water.

Humans are not the only organisms affected by drought. Without water, native plants may wither and animals may have to travel long distances to access water or die of thirst. The lack of water can lead to local extinction events or landscape or ecosystem changes in favor of species with lower water needs. Dry vegetation can also become fuel for wildfires sparked by lightning or human activity.

Life cannot exist without water, which is perhaps why the first cities formed along rivers. As with all natural resources, rules and regulations have been created surrounding the use and protection of this vital commodity. One of the most infamous and influential in the United States is the Colorado River Compact of 1922. The Compact was written during a noted wet period in history and allotted amounts of water from the Colorado River to the U.S. states of Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. This is the document regional water rights and laws have since been built upon. In spite of not taking into consideration, the water needs of Native Americans forced onto regional reservations or Mexico, each state was permitted to take a designated amount from the river. Mexico was eventually allotted water in a treaty signed in 1944, although the Colorado River runs dry before it reaches the Gulf of California.

Droughts have played an important role throughout history. They are suspected to have spurred human migration out of Africa and ended civilizations such as the Mayan Empire. The Dust Bowl hit the Great Plains region of the United States from 1930 to 1936. This displaced an estimated two million people and led to disease outbreaks that hit people weakened by malnutrition as a result of crop failures due to poor land management practices in the prior decades, topsoil erosion, and a severe drought.

As Earth’s climate continues to warm, models show dry places are likely to become drier. Rising temperatures facilitate quicker evaporation, increasing drought risk or prolonging ongoing droughts.

It is important to practice water conservation whether your region is experiencing a drought or not. On a larger scale, you can advocate for water conservation legislation by writing, calling, or voting for leaders who are working toward systemic change. Here are some things you can implement on a personal level.

  • Capture water you use while you are washing your hands or waiting for the shower to get warm and use that water to water plants or your garden.
  • Fix or call a plumber to repair any leaks in your plumbing or faucets.
  • Install low-flow fixtures or appliances, low-volume toilets, or retrofit existing faucets with flow restrictors.
  • Compost food scraps rather than putting them in the garbage disposal.
  • Plant native or drought-tolerant plants on your property.
  • Harvest rainwater.
  • Water plants and gardens by hand or choose water-efficient irrigation systems with a smart, weather-based controller and check the systems regularly to be sure they are watering plants and not pavement.
  • Reduce the amount of fertilizer you use as it increases the amount of water needed.
  • Mow your lawn at three inches or higher to encourage grass to root more deeply and hold soil moisture.
  • Mulch your garden to help the soil retain moisture and keep weeds at bay which would compete with your plants for water.
  • Keep your pool covered to minimize water evaporation.
  • Take shorter showers.
  • Only use the laundry machine or dishwasher when they are full, and use water-saving features if available.
  • Wash your car at a car wash that recycles water or wash it less often or not at all.


We chose to use the Global Precipitation Climatology Centre Drought Index (GPCC-DI) to represent global drought. This is an index dataset that combines several different measures of drought. This drought index is a combination of the Standardized Precipitation Index from Deutscher Wetterdienst (SPI-DWD), the Standardized Precipitation Evapotranspiration Index (SPEI), precipitation data from the Global Precipitation Climatology Centre, and temperature data from NOAA’s Climate Prediction Center in a one-degree grid. The advantage of a drought index is that it accommodates more than one type of drought. The GPCC-DI shows both meteorologic and hydrologic droughts.

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Writer
Sarah Appleton, National Geographic Society, National Geographic Society
GIS Specialist
Zoë Lieb, National Geographic Society
Last Updated

February 21, 2024

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