What is a drought?

Drought (Hugh Harris)

 

What is a drought? Droughts are not very easy to define. A drought is not just a lack of water for a significant period. It is difficult to come up with a single definition as drought varies from place to place. A severe drought in the Indian monsoon, such as that during the 2002 season, can be caused by just a few weeks of deficit rainfall. In south-east Australia, rainfall amounts have been below normal for about a decade, leading to an extended drought which has affected farming practices and has led to a series of wildfires in populated areas. In the UK people say there is a hose-pipe ban if it doesn’t rain for 14 days! In fact, there are a whole range of types of drought including; agricultural (farming), meteorological (weather), hydrological (surface water) and socio-economic (ones which affect humans). 

Agricultural drought This is a drought which affects how farmers can use their land. An agricultural drought usually means there is not enough water for the crops to grow as there is a lack of soil moisture. It can also affect livestock such as cows and sheep.

Hydrological drought Hydrological droughts are ones which there is a lack of water at the surface of the earth, resulting in less water in streams, lakes and reservoirs and can impact on the use of water for houses and industry.

Meteorological drought This is usually simply defined as a period where there has been less rain recorded. Rainfall amounts can vary by duration (i.e. time the rain fell for) and the intensity of rainfall (how hard it was raining). Meteorological drought is usually recorded in the time there has been little or no rain for e.g. months or years.

Socio-economic drought A Socioeconomic drought is when physical water shortages affects the lives of people; such as their health and quality of life. It can also affect the supply of food and materials and so affect the economy.

Did you know …

Large areas of ‘blocking’ high pressure over the UK can lead to long dry spells and can lead to a drought period as in 1976.  In 1976 rain was less than 60% of normal across the whole of the UK and the countryside turned brown! In South Wales, some homes had their water turned off for over 17 hours a day!

If climate change, greenhouse gases and global warming increase then the UK will experience more droughts especially in the south-east of the country. Even when we have normal amounts of rain, the high population density in England and Wales means there is less water available per person than in some Mediterranean countries who receive much less rain (EnvironmentAgency, 2009)

Defra (Department for Environment Food and Rural Affairs) manage droughts in England.

A heatwave lasted from June 22nd to July 16th in 1976 with temperatures reaching over 27C in many places in the UK.

Droughts can even happen at the poles where much of the precipitation falls as snow not rain!

 

Take home message …

Extreme weather, like a drought, is the type of rarely occurring event which hits the headlines, impacts on people’s livelihoods and sometimes leads to widespread loss of life and are more difficult to forecast by the very fact of its relative rarity.

Sources:

  • Peter Inness, “Understand the Weather”, 2010. Teach yourself (Hodder Headline).
  • The Met Office, “British Weather”, 2010. David & Charles
  • www.metlink.org 

 

HH@Metlink