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How does a drought happen?

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Quick answer

A drought happens when a region receives much less rain or snow than normal for weeks, months, or years. Soil dries, rivers and reservoirs shrink, and plants struggle. High temperatures make it worse by speeding evaporation. It ends only when steady rain returns and refills water supplies.

A drought develops when an area receives far less rain or snow than usual over months or years, drying out soil and reducing rivers and reservoirs. It worsens when high temperatures and strong evaporation remove remaining moisture, and it ends only when steady rainfall returns.

Step by step

  1. A region normally receives a predictable amount of rain or snow each season, which keeps soil and rivers supplied.
  2. When that precipitation is much lower than usual for an extended period, the water cycle in that area is disrupted.
  3. Soil moisture evaporates into the air, leaving plants without enough water to grow or survive.
  4. Streams and rivers shrink because they rely on runoff from rain and on groundwater that is no longer replenished.
  5. Reservoirs and wells drop as people continue to draw water for drinking, farming, and industry.
  6. The drought ends only when regular rainfall returns and steadily refills soil, streams, and reservoirs.

Key things to understand

  1. Drought begins when a region gets significantly less precipitation than its long-term average over weeks or months.
  2. Without regular rain, soil moisture evaporates and plants can no longer draw enough water through their roots.
  3. Streams, rivers, and reservoirs shrink because they depend on runoff from rain and on groundwater seeping in.
  4. Higher-than-normal temperatures increase evaporation, so the same shortfall of rain dries the land even faster.
  5. A drought ends only when sustained rainfall refills soil, streams, and reservoirs, which can take many months.

Labelled diagram

  1. Normal rainfall

    Regular rain or snow keeps soil moist and rivers flowing at usual levels.

  2. Rainfall deficit

    Precipitation drops well below average for weeks or months, starting the drought.

  3. Soil dries

    Without water, soil moisture evaporates and plants can no longer get enough water.

  4. Rivers shrink

    Streams and reservoirs fall because runoff and groundwater recharge stop.

  5. Heat speeds drying

    Higher temperatures increase evaporation, making the dry conditions worse.

  6. Rain returns

    Sustained rainfall refills soil, streams, and reservoirs, ending the drought.

How a drought develops and ends

Real-world examples

  • The Sahel region of Africa has suffered repeated multi-year droughts, causing crops to fail and livestock to die.
  • California experienced a severe drought from 2012 to 2016, forcing statewide water restrictions and shrinking reservoirs.
  • Australia's Millennium Drought lasted from 1997 to 2009, devastating agriculture in the Murray-Darling Basin.
  • Cape Town, South Africa, came close to running out of water in 2018 after three years of extremely low rainfall.

Common mistake

✗ Myth: A drought is just a long period of hot, sunny weather.

✓ Fact: Drought is defined by a shortage of water, not by temperature. A region can have a drought during cool weather if it simply does not receive enough rain or snow over a long period.

People also ask

What causes a drought?
Drought is caused by a prolonged shortage of precipitation, often when weather patterns shift and keep rain away. High temperatures increase evaporation, drying the land further. In some regions, ocean temperature changes like El Niño or La Niña alter wind and rain patterns, leading to months or years of unusually dry conditions.
How do droughts affect people?
Droughts reduce drinking water supplies, lower crop yields, and can cause food shortages and higher prices. Farmers may lose income, and cities may impose water restrictions. In severe cases, people are forced to leave their homes. Drought also increases the risk of wildfires and can damage ecosystems.
Can droughts be predicted?
Scientists can forecast drought risk weeks to months ahead by monitoring rainfall, soil moisture, and ocean conditions like El Niño. Long-term predictions are harder because many factors interact. Seasonal forecasts help farmers and water managers prepare, but the exact timing and severity of a drought remain uncertain.
What is the difference between a drought and a heatwave?
A heatwave is a period of unusually high temperatures, while a drought is a prolonged shortage of water. They often occur together because heat increases evaporation, but a drought can happen in cool weather if rain simply stops for a long time.
Can a drought happen in a rainforest?
Yes, even wet regions can experience drought if seasonal rains fail. The Amazon rainforest has had severe droughts when ocean temperature patterns shifted, reducing rainfall enough to stress trees and lower river levels.
How long does a drought last?
Droughts can last from a few months to several years, depending on the climate and the cause. A short dry spell may end with one rainy season, but a multi-year drought requires repeated seasons of above-average rain to fully recover.
What is a flash drought?
A flash drought is a rapid onset of drought conditions, often within weeks, driven by unusually high temperatures and strong winds that dry out soil quickly. It can catch farmers off guard because it develops much faster than a typical drought.

Part of the guide: Water & Weather Phenomena →