High Atmospheric Pressure and Its Role in Drought
Drought often begins when an area experiences an extended period of high atmospheric pressure. High pressure systems cause air to descend, which suppresses cloud formation because descending air warms and dries out. Without clouds, there is little chance of rainfall. For example, a region under a persistent high-pressure system for several weeks may see clear skies but no precipitation, leading to soil moisture depletion and water shortages.
This mechanism explains why some droughts can last for months; the stability of the high-pressure system prevents the usual weather fronts and storms from bringing rain. The lack of rainfall reduces river flows and groundwater recharge, affecting agriculture and water supply.
- High pressure causes descending air that warms and dries, inhibiting cloud formation.
- Persistent high pressure leads to prolonged dry conditions and drought.
- Example: A summer with a stationary high-pressure system over southern Europe can cause drought conditions.
Influence of ENSO and La Niña on Sea Surface Temperatures and Rainfall
The El Niño Southern Oscillation (ENSO) is a natural climate cycle involving periodic warming (El Niño) and cooling (La Niña) of sea surface temperatures in the central and eastern Pacific Ocean. These changes affect global atmospheric circulation and rainfall patterns.
During El Niño events, warmer sea surface temperatures increase evaporation, but the altered atmospheric circulation can suppress rainfall in some regions, such as parts of Australia and Southeast Asia, causing drought. Conversely, La Niña events feature cooler sea surface temperatures, which can enhance rainfall in some areas but cause drought in others, like the southwestern United States.
For example, the 2015-2016 El Niño contributed to severe drought in Indonesia by disrupting the usual monsoon rains. This shows how ocean temperature anomalies influence evaporation rates and atmospheric moisture, which in turn affect drought occurrence worldwide.
- ENSO includes El Niño (warm phase) and La Niña (cool phase) affecting Pacific sea temperatures.
- Changes in sea temperatures alter evaporation and atmospheric moisture.
- El Niño can reduce rainfall in some regions, causing drought; La Niña can have opposite or regionally variable effects.
- Example: 2015-2016 El Niño caused drought in Indonesia by disrupting monsoon rains.
Climate Change and Its Impact on Drought Frequency and Severity
Climate change refers to long-term shifts in global or regional climate patterns, largely driven by increased greenhouse gas emissions. It affects drought by altering temperature, evaporation rates, and atmospheric circulation.
Higher global temperatures increase evaporation from soils and water bodies, drying out the land faster. This can intensify drought conditions even if rainfall amounts remain similar. Additionally, climate change can shift weather patterns, making some regions drier and increasing the frequency or severity of droughts.
For instance, parts of southern Africa have experienced more frequent droughts in recent decades, linked to changing climate patterns. This demonstrates that climate change does not just cause drought by reducing rainfall but also by increasing water loss and changing atmospheric dynamics.
- Rising temperatures increase evaporation, drying soils faster.
- Climate change shifts weather patterns, potentially reducing rainfall in some areas.
- This can increase drought frequency and severity beyond natural variability.
- Example: Increased drought frequency in southern Africa linked to climate change.
Interconnections and Examples
These factors often interact. For example, a persistent high-pressure system may coincide with an El Niño event, compounding drought severity. Climate change may increase the likelihood of such combinations by altering atmospheric circulation patterns.
An example is the 2010 Russian drought, where a strong high-pressure system blocked rain and was influenced by broader climate variability. Understanding these links helps predict drought risk and informs water management strategies.
Recognising the combined effects of atmospheric pressure, oceanic cycles, and climate change is essential for managing drought impacts effectively.
- High pressure, ENSO events, and climate change can combine to worsen drought.
- Example: 2010 Russian drought involved persistent high pressure and climate variability.
- Integrated understanding aids drought prediction and management.
At-a-glance summary
Comparison table
| Step | Detail | Example | Exam Use |
|---|---|---|---|
| Identify atmospheric conditions | Recognise prolonged high pressure suppressing rainfall | Stationary high pressure over southern Europe in summer | Explain how descending air prevents cloud formation, reducing rain |
| Understand oceanic influences | Describe ENSO and La Niña effects on sea temperatures and evaporation | 2015-2016 El Niño causing drought in Indonesia | Link sea temperature changes to altered rainfall patterns |
| Explain climate change effects | Discuss increased evaporation and shifting weather patterns | More frequent droughts in southern Africa | Analyse how warming intensifies drought beyond natural cycles |
| Integrate factors | Show how atmospheric, oceanic, and climate factors combine | 2010 Russian drought with high pressure and climate variability | Explain combined causes to demonstrate complex drought origins |
Active recall
Quick check
1. How does high atmospheric pressure lead to drought?
High atmospheric pressure causes air to descend and warm, preventing cloud formation and reducing rainfall, which leads to drought.
2. What are ENSO and La Niña, and how do they affect drought?
ENSO is a climate cycle with El Niño (warm phase) and La Niña (cool phase) that change sea surface temperatures, affecting evaporation and rainfall patterns; these changes can cause drought in some regions.
3. In what ways does climate change influence drought?
Climate change raises temperatures, increasing evaporation and drying soils faster, and shifts weather patterns, which can increase drought frequency and severity.
4. Can drought be caused by a single factor?
Drought usually results from a combination of factors like high pressure, ENSO events, and climate change interacting to reduce rainfall and increase evaporation.