Climate
1.1 Definitions
- Weather
- State of atmosphere at any particular place at any particular time.
- Atmosphere
- Thin layer of gases around the earth surface
- Climate
- Average weather conditions at any particular place for a long period of time at least for 30 years
- Elements of Weather
- Temperature
- Rainfall
- Air Pressure
- Humidity
- Wind Speed
- Wind Direction
- Cloud Cover
- Most important are temperature and rainfall
- Climatic Zone
- A large continuous area with almost same type of climatic conditions
1.2 Climatic Zones Present in Pakistan
- Highland Zone
- In all the mountains of Pakistan, and the high areas of Balochistan
- Low Land Zone
- In the Indus plain excluding the deserts
- Arid Zone
- In the deserts
- Coastal Zone
- In the narrow coastal strip of Pakistan
1.3 Factors Affecting Temperature
- Altitude’s effect on temperature
- It is the height from the earth’s surface
- As we move up, temperature decreases
- The dust particles that absorb and trap heat are present in the surface at the low areas
- However these gases and dust particles are only present to the height of 12 miles (7 km) from the earth’s surface
- THEY REDUCE as we move higher, so less heat is trapped
- HOWEVER, if a sunny day comes out in a high area, such as in mountains, its extremely hot
- Because the gases that can block direct heat are not present
- Generally, lower temperature in high areas due to less dust particles and less gases to trap heat
- Distance from the equator
- Equator is the imaginary line at 0 degree of latitude that divides the earth into two hemispheres, the northern hemisphere and the southern hemisphere
- This is the area that is directly struck by suns’ rays very often
- These rays are the strongest over the equator
- However, the shape and intensity of these rays decrease as we travel away from the equator.
- Thus, as we travel towards either the north or south from the equator, temperature generally decreases.
1.4 Features of Climatic Zones of Pakistan
- Highland Climatic Zone
- Temperature conditions remain cold to very cold during winters
- Temperature conditions remain cool to moderate during summers
- In the Western Highlands, temperature remains cool to cold during winters and in summers the temperature remains warm to moderate
- Northern mountains receive almost every type of rainfall
- Ins ummers, there is monsoon and relief rainfall
- In winter, there are western depressions
- In spring and autumn, there is conventional current rainfall
- Western mountains receive mainly western depression rainfalls during winters
- Winters are long but summer sare short
- Precipitation in the form of snowfall during winters
- Lowland climatic zone
- Temperature conditions remain cool to cold during winters
- Temperature conditions remain hot during summers
- Lowland zone receives monsoon rain during summers, western depressions during winters and convectional current during spring and autumn with thunderstorm and hailing.
- Eastern part receives most rain during summers and western part receives most rain during winters
- Rainfall gradually decreases moving from north to south
- Features of coastal climatic zone
- Temperature remains moderate throughout the year due to sea breezes (the concept of monsoon rainfall but on small scale)
- Humidity level remains high especially during summer due to more evaporation from the sea
- Eastern cast receives more rain during summers from monsoon and western coast receives more rain during winters from western depressions
- Cyclonic rain during summers
- Arid climatic zone
- Temperature remains hot to very hot during summers
- Dust storms are common in summers
- Very less rainfall throughout the year
- Eastern desert receives little rain during summers from monsoon, and western deserts receive little rain during winters from western depressions
1.5 Types of Rainfall
- Monsoon
- Land becomes warm/cold quickly compared to the sea water
- Any area with high temperature will have low air pressure
- So land has lower air pressure compared to the sea and ocean during summers as it gets hot faster than the sea or ocean
- Winds always move form high air pressure areas (ocean and sea) toward low air pressure areas (land)
- Mid-July to Lid of September
- These winds enter Pakistan from three areas
- Directly from Arabian Sea form the south of Pakistan
- Mostly such monsoon occurs in coastal areas
- From the Bay of Bengal in India and Bangladesh
- These winds enter Bangladesh and India from Indian Ocean
- Winds move west towards Pakistan, entering Pakistan from Northern Mountains area (MAINLY HIMALAYAS, DON’T FORGET TO MENTION THIS)
- From arabian sea near rajasthan desert in India.
- However, very less winds from here as India has many hills and high places on this coast which blocks the winds
- Most important type of rainfall for the water resource of Pakistan
- Rainfall gradually decreases while moving from North to South
- Directly from Arabian Sea form the south of Pakistan
- These winds enter Pakistan from three areas
- Relief Rainfall
- As we studied in previous class, relief or topography refers to the natural physical features of land
- Mainly in Himalayas
- Process
- The warm and moist wind reaches a mountain or hill from one side
- We know that warm winds rise, while cold winds descend
- As the wind rises, it becomes cool and forms cloud
- So while still rising, many of these cloud start raining.
- This side from which the wind is rising is called windward side, where most of the rainfall is
- As the winds reach the peak, all of the form clouds and rains
- Then, the left over, now cold, winds start to descend on the OTHER SIDE
- This other side is called LEEWARD side
- IT HAS NO RAINFALL
- As no moisture is left to form clouds
- Thus, there is a rain shadow on leeward side
- Rain shadow means an area with no rain
- The cool and dry air descends on the leeward side
- The warm and moist wind reaches a mountain or hill from one side
- Convectional Current Rainfall
- Process
- The water evaporates from rivers and streams (water sources on the ground)
- Water transpired from the plants and trees
- Transpiration is the natural process were trees and plants lose their moisture
- As the warm air with this evaporated and transpired moisture rises
- It cools and forms clouds
- The clouds then cause rainfall
- Occurs between March – April
- And between October- November
- Hailing
- Thunderstorm
- Heavy rainfall
- High speed winds
- Upper and central Punjab, as well as lower Himalayas
- No Conventional Current Rainfall in Coastal Areas
- There is the concept of temperature inversion layer
- Usually, in other areas
- Temperature reduces as height increases (explained before)
- However, in coastal areas
- Land gets warned faster than sea
- So even at higher altitudes, there is high temperature
- The reason is that the hot air rises, but is trapped in the land-sea cycle
- So the higher temperature at higher areas mean that the moist warm air that is rising cannot form clouds as no coldness
- Even if clouds form, they scatter completely
- So there is no proper process of convectional current (warm air rising, cooling, and then rainfall) in coastal areas
- Process
- Cyclonic Rainfall
- How cyclones form
- In the ocean
- The warm winds rise from the ocean surface, and the lower area is replaced by colder winds (winds move from high pressure to low pressure)
- When this process happens again and again winds start to circle around this center area VERY FAST
- Also, they form clouds on the sides of this center area with heavy rainfall.
- Interestingly, there is no rainfall or any speedy wind in the center area
- The winds also start to move slowly towards the land
- Again high air pressure to low air pressure
- Summers
- Temperature required is 27 Degree Celsius
- Heavy rainfall
- Wind speed goes up to 120 km/h
- 10 kms high waves
- It happens only in coastal areas
- Coast se takra gaya cyclone
- Diameter of cyclones is between 200-300 kms
- How cyclones form
- Western Depression
- Cold winds from the Mediterranean sea
- Winters
- Dec-March
- After crossing Iran, Iraq and Afghanistan, these winds enter the western part of Pakistan
- More rain from these are in the Western parts of Pakistan
1.6 River Floods
- Water escaping the banks of the river
- Reasons
- Natural Reasons
- Melting of snow and glaciers during summers
- Heavy monsoon rainfall
- Especially in northern Punjab
- Human Reasons
- Deforestation on the foothills
- It increases erosion
- The soil is not held together by tree roots anymore
- As a result, the heavy rainfall can easily escape on the sides
- Also, the flow of water coming from mountains is not slowed down
- Embankments of rivers are not strengthened
- Their heights are not increased
- Dam failure
- Dams do not have the required capacity to store extra water
- Dam spills – major leakage in dams
- Deforestation on the foothills
- Natural Reasons
- How to reduce the flood risk
- Afforestation and reforestation
- Water flow reduces
- Less erosion
- River channel widened
- So water does not escape
- Embankments on side of river increased
- Extra channels build to contain the water during floods
- Take the water away from residential areas
- Reservoirs built to control river water and peak discharge
- Avoiding construction in commonly flooded areas
- Warnings issued to people through television, newspapers and radio
- If flood happens
- Evacuate people
- Rehabilitation facilities
- Afforestation and reforestation
- Explain how different groups of people are affected by floods and how their precautions
- Farmers
- Land becomes unusable till water removed
- Crops destroyed
- Food supplies lost
- High water table can damage future crops
- Can result in salination and waterlogging
- POSITIVE POINT
- Lands become alluvium rich
- Livestock and precious belongings can be moved to higher and safer places during flood season
- Local Residents
- Services cut off
- Mud houses broken
- Water borne diseases spread
- Precautions
- Higher places
- Alternative arrangements
- Transport Authorities
- Transport system destroyed (roads and railways)
- Routes are damaged
- Precautions
- Alternative plan for transport
- Repairment done urgently
- Farmers
- Flood benefits
- Nutrients back to soil
- Alluvium spread over large area
- Soil fertility improves
- Wetlands of Indus Delta stay healthy
- Overflow at upstream saves damage downstream
- Fish production in Arabian Sea increases
- Nutrients are brought from rivers
- Inland fish production and prawn species increases
- Nutrients from flooding
- Groundwater supplies replenished
- Water table increases
- Water table is height of water below earth
- Nutrients back to soil
1. 7 Droughts
- It is the severe lack of rainfall that results in complete destruction of most crips, and extreme water shortages. As a result, there is famine, disease and death on LARGE SCALE
- Types of Droughts
- Permanent Drought
- Crop cultivation is completely impossible if there is no irrigation
- Thal desert, Cholistan desert, Chagai area in Western Balochistan
- Seasonal Drought
- Well-defined rainy and dry spells
- Potwar Plateau and Southern Punjab
- Invisible Drought
- Water deficiency
- Crop yields (production per land area) reduces
- BUT not destroyed completely
- Unpredictable drought
- Abnormally low rainfall
- In an area where there is usually a humid climate
- Most dangerous
- For example, it occured in Murree area years ago
- Abnormally low rainfall
- Permanent Drought
- Causes of Droughts
- Natural Causes
- Monsoon winds are unreliable in some areas
- Moisture is reduced in sandy soil due to dry and hot weather
- Global climate constantly changing
- Pakistan’s climate affected
- Natural Causes
- Human causes
- Deforestation
- Soil erosion increases
- Rainfall reduces
- LESS transpiration
- Mismanagement of water resources
- Unlined canals
- No proper dams
- Will study in water resource chapter
- Unfair distribution of water between provinces
- Can lead to drought in some provinces
- Overgrazing of land due to nomadic herding etc.
- Soil infertility
- Lesser crop production
- Soil erosion
- No plants to hold soil together
- Global Warming increases due to human activities
- Causes climate changes
- Soil infertility
- Deforestation
- Effects of Droughts on natural (physical environment)
- Desertification
- Process where land that is previously not desert turns into one
- REMEMBER desertification is connected or overall rainfall pattern changing.
- Reasons
- Soil erosion
- Dust storms
- Desert areas extend
- Loss of vegetation
- Extinction of species (EXTREME OUTCOME)
- Rise in temperature
- Drying up of rivers, lakes and streams
- Fisheries and aquatic life harmed
- Algae grows in warm temperature in shallow waters
- This algea makes water unusable for humans
- Stops the growth of plankton
- Which is food for fish
- Fish die
- Drinking water unsafe
- Drop in water table
- Less water for plants (naturally) and for irrigation for humans
- Also less water for human use from groundwater sources
- Effects of droughts on human environment
- Population
- Widespread famine (food not available)
- Malnutrition, health deteriorates and starvation
- Deaths
- It cases anarchy
- Can lead to lawlessness
- Migration from drought areas
- Rural set-up breaks
- More pressure on city areas
- Nomadic lifestyle
- Difficult to provide services
- Widespread famine (food not available)
- Population
- Economy
- Crop failure
- Death of livestock
- Trade reduces
- Raw material reduces
- Industry is affected
- Exports reduce
- Imports of food increase
- Imports of other products increase
- Balance of payment negatively affected
- Economy is destroyed
- Crop failure
- Drought management
- Water storage schemes
- More reservoirs of dams and tanks
- Make irrigation canals to provide water for crop growing
- Afforestation and reforestation
- Use of new technology
- Desalination (removing of salt from sea water)
- Very expensive
- Reclaiming wastewater
- Water treatment
- Chemicals needed
- Expense
- Drought resistant crop varieties
- The crops that can survive in low water and rainfall, and can survive in high temperatures
- Genetically engineered varieties
- Lining canals to avoid absorption
- Planning of water resources
- Water conservation to avoid shortage
- Domestically using water less and carefully
- Setting priorities in allocation of water
- Use more water in activities that are most important
- Water conservation to avoid shortage
- The crops that can survive in low water and rainfall, and can survive in high temperatures
- Desalination (removing of salt from sea water)
- Water storage schemes
Lesson Tags
Climate | Weahter | Climatic Zones | Rainfall | Detailed Notes For Preparation & Revision | O Level Pakistan Studies 2059/02 and IGCSE Pakistan Studies 0448/02 | The Environment of Pakistan
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