The definition and impact of droughts

Droughts are extended periods of significantly reduced rainfall, leading to conditions where there is insufficient water to meet the needs of people, agriculture, and the environment.

The global distribution of drought events

Droughts occur across various regions of the world, often affecting areas with already dry climates more severely. Their distribution is influenced by geographical and climatic factors, with some regions experiencing more frequent events than others.

Regions prone to drought

• Arid climates - Areas with naturally low rainfall, such as parts of Australia, the southwestern United States, and certain regions of China, are highly susceptible when rainfall drops below normal levels.
• Conflict-affected zones - The Sahel region in Africa and parts of the Middle East, already stressed by war and instability, have faced intense drought events.
• Unexpected locations - Even typically wet areas can experience drought, such as the Amazon Basin in South America, where a significant drought impacted rainforest between 2002 and 2005.

The frequency of drought disasters varies globally, with some regions recording more events than others based on historical data.

Physical and human causes of droughts

Droughts result from a combination of natural processes and human activities that disrupt the water cycle or exacerbate dry conditions.

Physical factors contributing to droughts

• High-pressure weather systems - Dry, stable air masses prevent cloud formation and rainfall, creating prolonged dry spells.
• El Niño effects - This climate phenomenon brings high pressure and descending air over regions like Australasia, reducing rainfall and triggering drought conditions.
• Rising global temperatures - Increased heat leads to higher evaporation rates from land and water surfaces, depleting moisture reserves.
• Intertropical convergence zone (ITCZ) shifts - The ITCZ, a low-pressure belt near the Equator where trade winds meet, can fail to migrate as expected seasonally, depriving areas like parts of Africa of vital rains.

Human factors contributing to droughts

• Excessive irrigation - Overuse of water for agriculture depletes local water sources, worsening dryness in surrounding areas.
• Deforestation - Removing trees reduces transpiration, which can decrease local rainfall.
• Overgrazing - Livestock overgrazing exposes soil to erosion by wind, reducing the land's ability to retain moisture.
• Dam construction - Building dams can limit water flow to downstream regions, creating water scarcity in those areas.
• Intensive farming practices - Unsustainable agricultural methods exhaust soil moisture and degrade land, increasing vulnerability to drought.

Predictions on the frequency of droughts over time

Climate change and global warming are expected to influence the occurrence and intensity of droughts in the future. Scientific predictions highlight a trend towards more frequent and severe dry periods in many parts of the world.

Future trends in drought frequency

• Impact of warmer temperatures - Research from organisations like NASA indicates that rising global temperatures could lead to decreased rainfall and increasing drought occurrences.
• Regional projections - In the UK, forecasts from the Met Office suggest that extreme droughts might occur as often as once every decade in the future.
• Global implications - As climate patterns shift, areas already prone to dryness may face even harsher conditions, while new regions could become susceptible to drought events.