Geography Grade 12 Global and Regional Systems Study Guide

Climate and Weather Fundamental Concepts

• Mid-latitude cyclone: An intense low-pressure system characterized by a cold front and a warm front, occurring between $30^{\circ} - 60^{\circ}\,\text{N/S}$.

• Polar front: A zone of separation that develops at $60^{\circ}\,\text{N/S}$ of the Equator, separating cold polar easterlies from warm tropical westerlies.

• Cold front: The leading edge of a cold air mass separating cold air from warm air.

• Warm front: The leading edge of a warm air mass separating warm air from cold air.

• Undercutting: The process where cold air moves beneath warm air, forcing it to rise rapidly.

• Cyclone: An intense low-pressure cell where air rises and clouds form.

• Polar easterlies: Cold air blowing from the poles to the sub-polar low ($90^{\circ} - 60^{\circ}\,\text{N/S}$ of the equator).

• Tropical westerlies: Warm air blowing from the Sub-tropical high-pressure belt to the sub-polar low ($30^{\circ} - 60^{\circ}\,\text{N/S}$ of the equator).

• Backing: A change of wind direction from north-west to south-west (anticlockwise) in a mid-latitude cyclone in the Southern Hemisphere.

• Veering: A change of wind direction in a clockwise circulation on a mid-latitude cyclone in the Northern Hemisphere.

• Ridge: Elongated isobars associated with a high-pressure cell.

• Trough: Elongated isobars associated with a low-pressure cell.

• Tropical cyclone: An intense low-pressure system associated with severe storms.

• Vortex: A spiral motion of air in the center of a tropical cyclone, drawing surrounding air toward its center.

• Eye wall: The area near or around the eye of a tropical cyclone where the highest wind speeds, heavy rain, and cumulonimbus clouds occur.

• Latent heat: Heat released during condensation which contributes to unstable air and convection.

• Adiabatic heating: An increase in the temperature of descending air at a rate of $1\,^{\circ}\text{C}/100\,\text{m}$.

• Storm surge: An abnormal rise in sea level along a coast caused by onshore winds and the intense low pressure of a severe cyclone.

• Dangerous semi-circle: The south-western part of the tropical cyclone when it moves westerly.

• Temperature inversion: An increase in temperature with an increase in height/altitude.

• Local climate: The climate of a small-scale area.

• Katabatic winds: Cold, dense, and heavy air which blows from mountains to valleys due to gravity, typically during winter nights.

• Anabatic winds: Upslope warm and light winds which blow from the valley during the day.

• Inversion layer: A layer of warm air trapped between cold air masses.

• Thermal belt: An area in a valley where warm air is trapped between layers of cold air.

• Radiation fog: Fog formed when air in the valley cools to below the dew point temperature.

• Aspect: The direction a slope faces in relation to the sun's rays.

• Line thunderstorms: Thunderstorms arranged in a line along a trough of low pressure from North-West to South-East over the interior during summer.

• Moisture front: A boundary between two air masses with different moisture content and temperatures.

• Berg winds: Hot, dry, and gusty winds blowing from the interior down the escarpment to the coast in winter.

• Urban heat island: Higher temperatures over a city compared to the lower temperatures of surrounding rural areas.

• Pollution dome: A mass concentration of pollutants hanging above a city.

Mid-Latitude Cyclones (Frontal Depressions or Extra-Tropical Cyclones)

• Definition: Intense low-pressure systems with cold and warm fronts occurring between $30^{\circ} - 60^{\circ}\,\text{N/S}$.

• General Characteristics:     * Occur as a pair of fronts (warm and cold).     * Reach South Africa primarily in winter as pressure belts and wind systems move north.     * Move from West to East, steered by the westerlies.     * Air rotates clockwise around the low-pressure center in the Southern Hemisphere.     * Have a diameter of approximately $1000\,\text{km}$.

• Social Impacts:     * Positive: Winter rainfall provides water for irrigation, domestic, industrial, and agricultural use; snow in mountains attracts tourists.     * Negative: Heavy rain causes poor visibility and traffic accidents; strong winds and high seas pose hazards to fishermen in the South-Western Cape; extreme cold leads to power cuts and disrupted human activities; loss of human lives and livestock.

• Environmental Impacts:     * Positive: Melting snow replenishes dams, rivers, and underground water; potential rainfall for dry areas.     * Negative: Destruction of biodiversity and food chains; silting of dams; soil erosion from heavy rains; coastal flooding and landslides in mountain areas.

• Economic Impacts:     * Positive: Tourism boost from snowfall; winter crop production benefits the GDP; frost can kill off harmful organisms in the soil.     * Negative: Frost damages crops and livestock; floods damage property and reduce farmer income; high insurance claims; increased food prices due to storm surges destroying fishing tanks.

• Management Strategies:     * Avoid constructing infrastructure in low-lying areas.     * Minimize driving during low visibility and remain indoors.     * Shelter livestock in kraals or sheds during snowfall.     * Stock up on essentials (batteries, food, fuel, medication) before storms.

Tropical Cyclones

• Definition: Intense low-pressure systems developing in the easterly wind belt between $5^{\circ}\,\text{N/S}$ and $30^{\circ}\,\text{N/S}$.

• General Characteristics:     * Move from East to West, driven by tropical easterlies.     * Occur in late summer and early autumn.     * Average diameter is $500\,\text{km}$.     * The center is called the "Eye."     * Named alphabetically.     * Require sea surface temperatures of at least $26.5\,^{\circ}\text{C}$.     * Dissipate over land due to friction, lack of moisture, and lower temperatures.

• Associated Weather Conditions:     * Strong winds and torrential rainfall.     * Storm surges ($972\text{ to }978\,\text{hPa}$ isobaric readings typical).     * Towering cumulonimbus clouds around the eye.

• Case Study: Tropical Cyclone Eloise (2021):     * Made landfall on January $23$, $2021$, $20\,\text{km}$ south of Beira, Mozambique.     * Category $2$ cyclone with wind speeds up to $160\,\text{km/h}$.     * Recorded $250\,\text{mm}$ of rain in $24\,\text{hours}$.     * Affecting $441,686$ people, displacing $42,327$, causing $7$ deaths and destroying $20,798$ houses.

• Impact Categories:     * Social: Deaths, injuries, homelessness, and water-borne diseases.     * Economic: Loss of crops, business destruction, infrastructure damage, and trade disturbance.     * Environmental: Soil erosion, landslides, uprooting of trees, and destruction of biodiversity.

• Precautionary Measures:     * Evacuate low-lying areas.     * Build sea walls.     * Maintain electricity backups.

Subtropical Anticyclones and Local Wind Systems

• Definition: High-pressure systems found around $30^{\circ}$ latitude, associated with subsiding air and clear skies.

• Main Cells in Southern Africa:     1. South Atlantic High: Located over the Atlantic Ocean.     2. South Indian High: Located over the Indian Ocean.     3. Kalahari High: Located over the interior plateau.

• Seasonal Movement:     * Summer: ITCZ shifts south; South Atlantic and South Indian Highs move south; Kalahari High weakens, replaced by a thermal low, bringing summer rain to the interior.     * Winter: ITCZ shifts north; Kalahari High dominates, bringing dry stable weather; South Atlantic and South Indian Highs move north.

• Line Thunderstorms:     * Develop on the eastern side of a moisture front in summer.     * Cold, dry SW air from the South Atlantic High undercuts warm, moist NE air from the South Indian High.     * Forces warm air to rise rapidly, forming tall cumulonimbus clouds, heavy rain, hail, and lightning.

• Berg Winds:     * Hot, dry winds blowing from the plateau to the coast in winter.     * Air descends from the Kalahari High to a Coastal Low, heating at the dry adiabatic lapse rate ($1\,^{\circ}\text{C}/100\,\text{m}$).     * Create high fire risks (veld fires) and respiratory issues.

Geomorphology: Drainage Patterns and Landforms

• Drainage Patterns:     * Dendritic: Tree-like branches; tributaries at acute angles; uniform rock resistance (horizontal sedimentary or massive igneous).     * Trellis: Parallel main streams; tributaries join at right angles; alternating hard and soft folded rock.     * Rectangular: Main streams and tributaries have right-angle bends; following joints and faults in sedimentary rock.     * Radial: Streams radiate from a central highland (dome/volcano).     * Centripetal: Rivers flow toward a central depression or swamp.     * Deranged: Haphazard pattern; main rivers meander across floodplains; associated with melting glaciers.     * Parallel: Streams follow the slope of steep folded bedrock or major faults.

• Fluvial Landforms:     * Meanders: Bends in a river channel. Erosion occurs at the outer bank (cut-bank); deposition at the inner bank (point bar/slip-off slope).     * Oxbow Lake: A cut-off meander loop filled with water.     * Braided Stream: River splits into smaller channels as it deposits its load on its own bed.     * Flood Plain: Flat land on river banks formed by repeated flooding and deposition.     * Natural Levees: Raised banks formed by sediment deposition during floods.     * Deltas: Landforms at the mouth of a river where it splits into distributaries and deposits its load as velocity decreases.

• River Grading:     * Graded Profile: A smooth concave longitudinal profile where erosion and deposition are in balance.     * Ungraded Profile: Contains knickpoints (waterfalls/rapids).     * Base Levels: Ultimate base level is sea level; temporary base levels include dams, lakes, or waterfalls.

• River Rejuvenation: Occurs when a river gains energy (e.g., due to land uplift or sea-level drop), causing vertical erosion.     * Features: Knickpoints, terraces, incised/entrenched meanders, and valleys-within-valleys.

• River Capture (Stream Piracy):     * Process where an energetic river (captor) intercepts the headwaters of a less energetic river (captured).     * Features: Misfit stream (too little water), elbow of capture (right-angle bend), and wind gap (dry valley).

Settlement Geography

• Classification:     * Rural: Uni-functional (primary activities like farming); low population; can be dispersed (scattered) or nucleated (clustered).     * Urban: Multi-functional (secondary and tertiary activities); high population; nucleated.

• Site and Situation:     * Site: Exact piece of land where a settlement is built (influenced by soil, water, relief, fuel).     * Situation: Location relative to the environment (proximity to markets, roads, airports).

• Shapes:     * Linear: Along a feature like a road or river.     * Round/Circular: Around a central point like a church or well.     * T-shaped/Crossroads: At major intersections.

• Land Reform in South Africa:     * Pillars: Land Redistribution (providing land access), Land Restitution (compensating for past forced removals), and Land Tenure Reform (securing rights for residents on others' land).     * The Expropriation Act of 2024: Provides a framework for the state to acquire land for public purpose/interest, allowing for nil compensation in specific cases.

• Urban Structure:     * CBD (Central Business District): High land value, tallest buildings, grid-iron street pattern.     * Transition Zone: Mixed functions, dilapidated buildings (urban blight), expansion zone for CBD.     * Rural-Urban Fringe: Mixture of rural and urban functions (airports, golf courses, shopping malls).

• Urban Issues:     * Urban Sprawl: Uncontrollable expansion.     * Informal Settlements: Illegally built on land with cheap materials; lack basic services; subject to fires and disease.

Structure of the Economy

• Sectors:     * Primary: Extraction of raw materials (mining, fishing, agriculture).     * Secondary: Processing raw materials (manufacturing, industries, construction).     * Tertiary: Service industry (trade, transport, education).     * Quaternary: Specialised professional services (research, administration).

• Case Study: Sugarcane Farming:     * Main provinces: KwaZulu-Natal and Mpumalanga.     * Challenges: Electricity rates increase ($12.7\%$ in $2025/26$), sugar tax (levied at $2.1\,\text{cents}$ per gram of sugar exceeding $4\,\text{g}/100\,\text{ml}$), and climate variability.

• Case Study: Gold Mining:     * South Africa has $90$ gold mines, mainly in Gauteng, Free State, and Northwest.     * Production: Reported at $100,000,000\,\text{kg}$ in December $2024$ (down from $104,000,000\,\text{kg}$ in $2023$).     * Estimated exhaustion of resources in $33\,\text{years}$.

• Industrial Regions:     * PWV (Gauteng): Largest core; chemical, iron, and steel industries.     * Durban-Pinetown: Second largest; export-oriented; shipbuilding, textiles, and chemicals.

• Development Strategies:     * RDP (Reconstruction and Development Programme): Launched in $1994$ to address apartheid inequalities.     * GEAR (Growth, Employment and Redistribution): Macroeconomic policy from $1996$ focusing on fiscal discipline and trade liberalization.     * IDZ (Industrial Development Zones): Export-oriented estates (e.g., Dube Trade Port near King Shaka International Airport).     * SDI (Spatial Development Initiatives): Targeted geographic development (e.g., Maputo Development Corridor between Gauteng and Mozambique).

• Urbanization and Trade:     * South Africa's GDP is significantly bolstered by manufacturing ($15.2\%$) and finance/real estate ($21.5\%$).     * The informal food sector accounts for $40\%$ of the food market, valued at approximately $R404\,\text{billion}$.

Oxbow Lake Formation:

• Definition: An oxbow lake is a U-shaped body of water formed when a meander from a river gets cut off.

• Formation Process:

  1. Erosion and Deposition: Rivers often flow in curves called meanders. As the river bends, the outer bank experiences erosion while the inner bank accumulates sediment (deposition).

  2. Narrowing of Meander Neck: Over time, as erosion continues, the neck of the meander narrows due to the continuous flow of water and cutting processes.

  3. Cut-off Occurrence: Eventually, during a flood or high water event, the river may achieve sufficient force to cut through the narrow neck, creating a new straighter river channel.

  4. Isolation of Oxbow Lake: The old meander loop is left isolated from the main river flow, forming an oxbow lake. It often becomes shallower and may eventually silt up or become a wetland.

Tropical Cyclones:

• Definition: An intense low-pressure system developing in the easterly wind belt between $5^{ ext{N}}$ and $30^{ ext{N}}$.

• General Characteristics:

  • Move from East to West, driven by tropical easterlies.

  • Most prevalent during late summer and early autumn when sea surface temperatures are highest, requiring temperatures of at least $26.5^{ ext{C}}$.

  • The storm exhibits strong winds, torrential rainfall, and the characteristic "eye" at its center.

• Associated Weather Conditions:

  • High winds, storm surges, and significant cloud formation, particularly cumulonimbus around the eye, leading to severe weather impacts.