Impacts of Climate Change and Tropical Revolving Storms (AQA A-Level Geography): Revision Notes

Impacts of Climate Change and Tropical Revolving Storms

Understanding tropical revolving storms

Tropical revolving storms are powerful, rotating weather systems that develop over warm tropical oceans. These storms are known by different names depending on where they occur in the world, but they all share similar characteristics and formation processes. Understanding where they form, how strong they can become, and how climate change is affecting them is essential for predicting their future behaviour and preparing communities.

Distribution of tropical revolving storms

These powerful weather systems develop in specific tropical regions between 5° and 20° latitude on both sides of the Equator. Once they form, they typically move westward and reach their most destructive force in particular areas.

Regional names and locations

Different parts of the world use different names for these storms:

• Hurricanes form in the Caribbean Sea and Gulf of Mexico region, accounting for 11% of all tropical revolving storms globally
• Hurricanes also develop on the western side of Central America in the eastern Pacific Ocean (17% of all storms)
• Cyclones occur in the Arabian Sea and Bay of Bengal area (8% of all storms)
• Typhoons develop off southeast Asia, representing the largest proportion at one-third of all storms occurring worldwide each year
• Cyclones also form near Madagascar in the southeast African region (11% of storms)
• Willy-willies is the local name given to storms in the north-western and north-eastern regions of Australia (20% of global storms)

Seasonal patterns

Each region experiences these storms during specific seasons. For example, hurricanes in the Caribbean typically occur from August to October, while typhoons in East Asia happen between May and December. These seasonal patterns are linked to when ocean temperatures are warmest in each region.

Magnitude and classification

Understanding the strength of tropical revolving storms is crucial for warning systems and emergency preparations.

The Saffir-Simpson scale

Tropical revolving storms are measured using the Saffir-Simpson scale, which classifies storms into five categories based solely on wind speed. This scale helps authorities and communities understand the potential danger of an approaching storm.

The five categories range from:

• Category One (least intense): wind speeds of 119-153 kph
• Category Two: wind speeds of 154-177 kph
• Category Three: wind speeds of 178-208 kph
• Category Four: wind speeds of 209-251 kph
• Category Five (most intense): wind speeds of 252 kph or greater

Limitations of the scale

There is ongoing debate about whether the Saffir-Simpson scale should be revised or replaced. The scale only measures wind damage, but research shows that nearly 90% of deaths from tropical storms in the United States result from water-related hazards rather than wind. These water hazards include storm surges, extreme rainfall, and inland flooding, which the current scale does not directly measure.

The impacts of climate change on tropical revolving storms

Climate change is altering the behaviour and characteristics of tropical revolving storms in significant ways. Research has provided important insights into how these changes are occurring and what we might expect in the future.

Evidence of changes since 1970

In 2005, researchers published findings examining changes in tropical cyclone patterns since 1970, when reliable satellite data became available. Their analysis revealed important trends:

• Overall, the total number of cyclones globally has decreased
• However, in the North Atlantic Ocean specifically, there has been a significant increase in both the number and proportion of very strong cyclones
• The intensity of storms in certain regions has increased notably

Why is climate change affecting storms?

The increase in ocean temperatures caused by climate change creates conditions that lead to more intense storms. Here's how this process works:

Increased ocean warming leads to:

1. Higher air temperatures above the warmer water surfaces
2. Enhanced uplift (rising of warm, moist air) which lowers atmospheric pressure at the surface
3. Greater oceanic evaporation, which increases the amount of water vapour in the atmosphere

These factors then work together in a feedback process. When parcels of very moist air rise and cool at higher altitudes, they release enormous amounts of latent heat through condensation. This further strengthens the uplift process, creating more powerful storm systems.

Predictions for 2100

Scientists have used climate models to predict how tropical storms might change by the year 2100. While predictions vary between different models, the general consensus suggests:

• An increase of 2-11% in the average intensity of storms
• A decrease of between 6% and 34% in the total number of tropical storms
• A substantial increase in the frequency of the most intense storms (Categories 4 and 5)

This means that while we might see fewer storms overall, the ones that do form are likely to be significantly more powerful and destructive.

Slow-moving storms

A study published in 2017 identified another concerning trend: tropical storms are slowing down. As polar regions warm due to climate change, there is less difference in atmospheric pressure between the poles and the tropics. This reduced pressure gradient means the winds that normally push storms along are becoming weaker, causing storms to move more slowly across the landscape.

Why slower storms are more dangerous:

Slow-moving storms can produce significantly more rainfall because they remain over the same area for longer periods. Research suggests there could be a 20% increase in precipitation falling within 100 km of a storm's centre. This enhanced rainfall is further amplified by the greater amount of water vapour carried in the warmer atmosphere. Additionally, slower storms increase wind damage simply because strong winds affect areas for longer periods. They also create larger walls of seawater (storm surges) in front of them, increasing the potential for devastating coastal flooding.

Case study: Hurricane Florence (2018)

Hurricane Florence provides a clear example of how climate change is influencing storm impacts. This Category 1 hurricane moved very slowly after making landfall in North Carolina, USA, in September 2018. The storm remained nearly stationary for several days, causing widespread and prolonged flooding.

The impacts of tropical revolving storms

The damage and disruption caused by tropical revolving storms depend on multiple interconnected factors. Understanding these helps explain why some storms cause much more damage than others, even when they have similar wind speeds.

Factors affecting vulnerability

Several factors determine how vulnerable a location is to storm damage:

• Storm intensity (Categories 1-5 on the Saffir-Simpson scale)
• Speed of movement - slower storms cause more damage as they affect areas for longer
• Distance from the sea - areas further inland typically experience less severe impacts
• Physical geography - the width of coastal plains, presence of river deltas, and location of mountain ranges all influence impact severity
• Community preparations - whether adequate warning systems, evacuation plans, and protective infrastructure exist
• Warning and response - how quickly authorities issue warnings and how effectively communities respond

Primary impacts

Tropical revolving storms create three main types of direct impact, each capable of causing severe damage and loss of life.

Winds

The powerful winds associated with these storms can often exceed 150 km/hr, with Category 5 events experiencing winds over 250 km/hr. These extreme winds cause several types of damage:

• Structural damage to buildings, with winds strong enough to cause buildings to collapse entirely
• Destruction of roads, bridges, and other infrastructure
• Bringing down electricity transmission lines, leaving areas without power for extended periods
• Devastating agricultural areas by destroying crops and farm buildings
• Creating dangerous flying debris that poses a serious threat to people and property

The massive amounts of debris flung about by the winds create additional hazards, damaging anything in their path.

Heavy rainfall

Tropical storms bring intense rainfall that commonly ranges from 200mm to 300mm, though higher amounts frequently occur. This extreme precipitation causes multiple problems:

• Severe flooding across wide areas, both near the coast and inland
• Landslides on steep terrain where heavy rain saturates the soil
• Mudslides in areas with loose soil or deforested slopes

In coastal areas with high relief (elevation), rainfall amounts can increase dramatically to over 500mm per day. This is particularly dangerous as it combines with other storm impacts to create compound disasters.

Storm surges

Storm surges occur when strong winds push ocean water towards the coast, causing sea levels to rise dramatically as a result of lower atmospheric pressure in the storm. These surges create walls of water that surge inland.

Storm surges have a particularly devastating effect on low-lying coastal areas. River deltas are especially vulnerable because flooding can extend far inland along river channels. During major storm events, agricultural areas near the coast can suffer damage for extended periods as the soil becomes contaminated by sea water, making it unsuitable for farming until the salt can be washed away or broken down naturally.

Responses to storm hazards

Modern technology and scientific understanding have greatly improved our ability to predict and prepare for tropical storms.

Preparedness

Advances in data collection and analysis mean that tropical storm prediction has become increasingly sophisticated and accurate. This improved forecasting gives communities more time to prepare and potentially save lives.

Modern forecasting systems:

Weather bureaus, such as the National Hurricane Centre in Florida, USA, use multiple data sources to track and predict storms:

• Weather satellites provide real-time views of storm location, track, size, and strength from space
• Specialised aircraft fly directly into hurricanes to investigate their structure and gather detailed measurements
• Weather balloons collect atmospheric data at different heights
• Powerful supercomputers analyse all this data from different sources to predict storm paths and intensity changes

These forecasting systems allow authorities to issue timely warnings to communities in the path of approaching storms, giving people time to evacuate to safer areas or secure their property. The more accurate the predictions, the more effective the preparations can be.