Find out why drought occurs and how you can help by using water wisely.
What is drought?
There is no single definition of drought. Whilst a drought will be caused by shortage of rainfall, the nature, timing and impacts vary according to location and the different sectors affected such as public water supply, agriculture and industry.
A long drought in winter may not be obvious as the weather is cold, but it can cause problems for public supply if groundwater and reservoirs don't refill. A short drought in summer may be very visible as soil and small streams dry out, affecting farmers and the environment first.
Why do we still get floods during a drought?
Heavy rain can cause flooding at any time, including during a drought.
In a drought soil dries out and may harden, so heavy rain quickly runs off the top into rivers and streams, causing flooding downstream.
During a drought, rain benefits the environment in the short term, but in the summer much of the rain is taken up by plants or evaporates. This means that water may not seep through the soil to the underground aquifers.
So when dry weather returns there is not enough water stored and drought conditions remain.
Across England and Wales we apply these three categories relating to drought:
Temporary use restrictions
Water company drought plans have required them to implement restrictions such as hosepipe bans to help conserve supplies. Farmers, other abstractors and the environment are also likely to be adversely affected. Groundwater stores will not be replenished by short-lived periods of rainfall.
Environmental stress due to rainfall deficit
Farmers, other abstractors and the environment are at risk of adverse effects from long-term, significantly below average rainfall. Rivers and lakes may show short term responses due to rainfall but groundwater stores remain in deficit.
We class low groundwater as sites that are notably or exceptionally low for the time of year. Groundwater takes longer to respond to rainfall than rivers and reservoirs, and sometimes it may not respond as moisture is taken up by plants or evaporates as temperatures rise.
How does the Environment Agency determine drought categories?
- We consider a range of hydrological and environmental triggers across the different sectors and the geographic area affected
- We look at water resource prospects and how likely it is the situation will get worse. This will include the timing and season
- We assess the level of actions we and water companies are taking or are about to take in line with our drought plans
- We consider the extent of public and media interest so that people are well informed and can help - for example by saving water
The decision to move to drought or other status is an expert judgement based on all these factors.
The main aspects of drought and the impacts, risks and triggers we monitor are set out in our drought plans. They include the following aspects and will tend to occur in the order below:
- Meteorological - shortage of rainfall and actual evaporation
- Hydrological - reduced river flows and low groundwater levels
- Environmental - dry soils, stress on habitats and wildlife
- Agricultural - dry soils, need for irrigation and stress on plants
- Public supply - low reservoir storage, high demands, customer appeals and restrictions, and drought permits and orders
Find out more about the different kinds of drought and their effects: