Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: Prolonged High Pressure Systems
High pressure systems, also known as anticyclones, play a crucial role in creating drought conditions around the world. When these systems become "stuck" or persistent over an area for weeks or even months, they can lead to serious environmental consequences.
Key Definitions:
High pressure systems form when air sinks toward the Earth's surface. As it descends, the air compresses and warms. This warming reduces the relative humidity, making cloud formation difficult. Without clouds, there's little chance of precipitation, creating perfect conditions for drought to develop.
Certain regions are more prone to persistent high pressure systems. These include subtropical areas around 30° latitude (where many of the world's deserts are located) and mid-latitude regions during certain seasons. Climate patterns like El Niño can influence where these systems develop and how long they persist.
Prolonged high pressure systems contribute to drought through several interconnected mechanisms that create a feedback loop of dry conditions:
The descending air in high pressure systems prevents cloud formation, leading to increased sunshine and higher temperatures. This increases evaporation from soil and water bodies.
The outward flow of air at the surface creates winds that can further dry out soils and vegetation. These winds can also prevent moisture-laden air from entering the region.
As soil dries out, less energy goes into evaporation and more into heating the air, creating a feedback loop that intensifies drought conditions and can lead to heatwaves.
Sometimes high pressure systems become "stuck" in place for extended periods. These are known as blocking patterns and are particularly important for understanding prolonged droughts.
Blocking occurs when the normal west-to-east flow of weather systems is disrupted. This happens when the jet stream (a fast-flowing air current in the upper atmosphere) develops large meanders or loops. When these loops cut off, they can create persistent high pressure regions that remain stationary for weeks.
During a blocking event:
In 2018, a persistent high pressure system remained over Northern Europe from May to August. This blocking pattern diverted rain-bearing weather systems away from the region, resulting in one of the most severe droughts in recent European history. Temperatures soared to record levels and rainfall was up to 80% below normal in some areas.
The impacts included:
Australia is particularly vulnerable to prolonged high pressure systems. The "Blocking High" over the Tasman Sea was a key factor in the devastating Millennium Drought (1996-2010) and more recent droughts. These systems prevent moist air from the Pacific from reaching inland areas, creating long periods without rainfall.
During California's 2012-2016 drought, meteorologists identified a persistent high pressure system over the northeastern Pacific Ocean that they nicknamed the "Ridiculously Resilient Ridge." This system blocked winter storms from reaching California for multiple years, leading to the state's worst drought in 1,200 years.
Research suggests that climate change may be affecting the frequency and persistence of high pressure systems in several ways:
These changes could lead to more frequent and severe droughts in regions not historically prone to them, creating new challenges for water management and agriculture.
The 2020-2022 drought in California and the wider Western United States was exacerbated by persistent high pressure systems that diverted rainfall away from the region for multiple consecutive winters. Scientists found that this drought was made approximately 20% more severe by human-caused climate change, which intensified the high pressure systems and increased temperatures.
Key impacts included:
Meteorologists use several tools to monitor and predict high pressure systems:
Satellites can track cloud patterns (or lack thereof) associated with high pressure systems and monitor their movement and persistence.
Weather maps showing isobars (lines of equal pressure) help identify the location and strength of high pressure systems.
Advanced computer models can predict the development and movement of high pressure systems, though long-term blocking events remain challenging to forecast accurately.
Understanding prolonged high pressure systems is crucial for environmental management, particularly for:
By monitoring atmospheric patterns and understanding the mechanisms behind prolonged high pressure systems, environmental managers can better prepare for and mitigate the impacts of drought conditions.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.