Drought develops when a region receives less water than it normally gets for an extended time. It can begin quietly with weeks of below-normal rain or snow, then grow into a serious problem over months or years. Drought matters because it affects crops, drinking water, rivers, ecosystems, energy production, and local economies.
Understanding the stages helps people prepare before water shortages become severe.
A drought usually starts as meteorological drought, which means precipitation is lower than normal. If dry weather continues, soil moisture drops and plants become stressed, causing agricultural drought. Over longer periods, streams, lakes, reservoirs, and groundwater decline, creating hydrological drought.
When these water shortages affect jobs, food prices, health, and daily life, the drought has socioeconomic impacts.
Key Facts
- Meteorological drought means precipitation is below the long-term average for a region.
- Agricultural drought occurs when soil moisture is too low to support healthy crops and vegetation.
- Hydrological drought occurs when rivers, reservoirs, lakes, snowpack, or groundwater fall below normal levels.
- Water balance can be estimated as Change in storage = Precipitation - Evaporation - Runoff - Water use.
- Drought severity depends on precipitation, temperature, evaporation, soil type, vegetation, and human water demand.
- Drought can last for weeks, months, or years, and its impacts often appear later than the rainfall shortage.
Vocabulary
- Drought
- A drought is a long period of unusually low water supply compared with what is normal for a place.
- Precipitation
- Precipitation is water that falls from the atmosphere, including rain, snow, sleet, and hail.
- Soil moisture
- Soil moisture is the water held in soil that plants can use for growth.
- Groundwater
- Groundwater is water stored underground in the spaces between soil particles and rocks.
- Reservoir
- A reservoir is a natural or human-made lake used to store water for drinking, irrigation, energy, or flood control.
Common Mistakes to Avoid
- Thinking drought only means no rain at all. A drought can happen when rainfall is below normal, even if some rain still falls.
- Confusing weather with climate. A dry week is a weather event, but drought is a longer-term water shortage compared with normal conditions.
- Assuming drought affects all water sources at the same time. Soil moisture can drop quickly, while groundwater and reservoirs may decline more slowly.
- Ignoring human water use. High irrigation, industry, and household demand can make a natural dry period much more damaging.
Practice Questions
- 1 A town normally receives 80 mm of rain in April but receives only 35 mm this year. How many millimeters below normal is the rainfall, and what percent of normal rainfall did the town receive?
- 2 A small reservoir holds 120 million liters at the start of summer. During a dry month, 8 million liters enter from streams, 18 million liters evaporate, and people use 25 million liters. Using Change in storage = Inflow - Evaporation - Water use, what is the reservoir volume at the end of the month?
- 3 Explain why a region can enter agricultural drought before it enters hydrological drought. Include soil moisture, crops, and water stored in rivers or groundwater in your answer.