Climate

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Lesson Objectives

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

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Lesson Objectives

• 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

• 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

• 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

• 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

• 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

• 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

• 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

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

• 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

  • 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

• 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

  • 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

• 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