Climate
Def|n|t|ons
Climateisa generalization of the day to day weather conditions over a long period of time,
usually over 30 years.
e Weather refers to the atmospheric conditions e.g. temperature, humidity, rainfall and pressure
of any place for a short period of time. It is often localized.
e Humidity
is the amount of water vapor present in air.
e Condensation is the conversion of water vapors into liquid due to which clouds are formed.
Temperature key
40°C and above (very hot)
e 31°C - 39°C (hot)
e 21°C - 30°C (warm)
e 10°C - 20°C (mild)
e 03°C - 09°C (cool)
e -5°C-02°C (cold)
e Below -5°C (very cold)
Climate zones
e Highland climate
e Lowland climate (semi — arid)
e Coastal climate (humid)
* Arid climate (arid)
Highland climate
Northern mountains
e Cold/very cold winters
* Mild summers.
e Rainfall in all seasons (mainly in the form of snow in winter)
e Largedaily range
Western mountains
e Cold winters
e Warm summers
e Winter rainfall/western depression
e Largedaily range
Semi — arid/lowland climate (UIP + LIP + Potowar Plateau)
e Cool/cold winters
e Hot summers
e They receive high monsoon rainfall
e Dryness/aridity increases from north to south
e Largedaily range
Humid/coastal climate
Karachi coast
* Mild winters
e Warm summers
e Monsoon rainfall (Arabian sea)
e Tropical cyclones
e Short daily range
Makran coast
* Mild winters
e Warm summers
e Rainfall from winter depressions (from Iran)
e Tropical cyclones
e Short daily range
Arid climate (Deserts e.g. Thar and Kharan)
* Mild winters
e Hot/very hot summers
e Extreme aridity due to little rainfall
e Llarge daily range
e Dust storms
Factors influencing temperature
® Latitude
o Altitude
e Distance from sea
Latitude/angle of sun
e Temperatures are very high near the equator
e As we move down/up the equator towards the north or south pole, temperature decreases
e Thisis because rays spread over a larger area due to the low angle of the sun
Altitude/height of land
e As heightincreases, temperature decreases
® .. Asairisless dense so holds less heat
® Heat radiated from the surface decreases from height
e Fall of 5°C for every 500m in height in dry or arid air like of Pakistan
Distance from sea
Maritime influence (sea)
e Climate influenced by sea giving low range of temperature between summer and winter
® Places near coast are cooled by sea in summer and warmed by it in winter as water absorbs and
releases heat slowly
Conditional influence (land)
® Landis not under sea influence i.e. are too far from sea
e Inthese inland areas, temperature is high in summer as land heats up rapidly
e Butin winter, land gives off heat rapidly and so locations experience colder winters
Sources of rainfall in Pakistan
* Monsoon winds
e Western depression
e Convectional currents (causing thunderstorm)
e Tropical cyclones
* Relief
Monsoon winds
e Moisture bearing winds carrying rain
e Blow from Bay of Bengal and move from East to West
e After crossing Bangladesh and northern India, the tail end of the winds enter northern Pakistan
® Across UIP towards northern areas
e ..due to low pressure there
® Rise overland
® Moisture condenses
e So clouds are formed therefore heavy rainfall
* Some monsoon winds blow blow across south — east Pakistan from the Arabian Sea
® These are weak winds and have little effect
e However, sometimes an over
— active monsoon system brings heavy monsoon rainfall in Karachi
Causes of monsoon at Karachi
e Low pressure develops over land
e Draws in wind from high pressure are:-
o From the Arabian Sea
* Moisture bearing/wet winds carrying rain/humid
e Rise over land
e Cools
* Moisture condenses
Importance of monsoon rainfall to people of urban areas
e Cooler
— better working and living conditions due to pleasant climate
e Fresher —less air pollution, cleaner air
e Water supply for drinking, factories, market and gardens
Q: Explain why the lack of monsoon rainfall in southern Punjab and Sindh causes
problems for farmers.
e Poor crop growth
e Low profit/income
e Little or no other source of rain e.g. no western depressions, relief rainfall, etc.
e High evaporation/evapotranspiration
o Due to high temperatures
e Need for irrigation which is expensive
e Poor farmers cannot afford tubewells and other irrigation methods
e Can be soil erosion through blowing
Western depressions
These are the cyclones that originate in the Mediterranean Sea
They travel across Afghanistan and Iran
They then reach western areas of Pakistan
Bring monsoon
Rise over land
Clouds causing condensation
So clouds are formed
This rainfall occurs during December to March
Quetta receives most of its rainfall through western depressions (coming from Iran)
Advantages and disadvantages of winter rainfall in northern Pakistan
Advantages
o Fills reservoirs and rivers — so more storage
Water available for HEP production
O
Water for Barani crops
0
Water for rabi/winter crops/fruit trees
0
Water when everything else is frozen in northern areas
0
Lighter form of rain — can suck in therefore more ground water
0
o Snow for tourism due to scenic beauty
Disadvantages
o Many fall as snow so of little use
This is because rivers/lakes are frozen
0 o0 O
00
Damage to environment — landslides, avalanches, etc.
Damage to roads —blockage, slippery, etc.
Silt collects in reservoirs/dams
Difficulty meaning farmers must do transhumance orthey are to live a nomadic life
Convectional currents
At the start and end of summer due to high temperatures
Moisture evaporates from rivers/lakes/vegetation, etc.
(moist) air rises
Air cools as it rises
Causes condensation of moaisture
... which causes rainfall often as thunderstorms
Northern and north — western areas get this rainfall mainly in Peshawar and Rawalpindi
They are caused from April
to June
They are also caused from September
to November
Tropical cyclones
e These may bring a few hours of very heavy rainfall with destructive winds to the coastal areas
e Originate from Arabian Sea quite often but rarely reach coastal areas of Pakistan
e They are caused from April
to June
e They are also caused from September
to November
Q: Explain how storms such as these may effect industry and communications in
urban areas.
* Flooding/heavy rain
e Strong winds
e Lightning strikes
e Damage or closure of buildings, roads, bridges and airports
® Lack of deliveries
® Loss of production/work stops
e Labor cannot get to work
e Lack of experts/investors linked to airports being closed
® Loss of telecommunication
e Loss of power (electricity)
Relief rainfall
e Relates to height of a land
e Itoccurs where moist unstable air moves up after striking against a mountain side — so it rises
e Itis chilled on reaching a certain height
e This chilling causes heavy condensation and precipitation on the ‘wind ward’ side
e The leeward side (the other side of the mountain) receives sinking warm air and a dry rain
shadow area is usually formed
e Areas having high altitude receive this rainfall e.g. northern mountains
Q: Feasibility of improving water supply to farmers in Punjab and Sindh
e Advantages
o Rainfall in monsoon season can be stored
Snow melt from mountains
0
Indus river system brings water from highlands
0
Can make more storage of reservoirs of dams and barrages
o o0
Can build more canals
o Can use ground water and therefore more tubewells can be built
e Disadvantages
o Cost of reservoirs or canals
Cost of tubewells
O
Lack of reservoirs and barrages
000 O0O0O0
Indus Water Treaty limits supply
Lower water table restricts ground water
Water logging and salinity problems
Cost of power supplies for pumps
Other constraints e.g. education, wastage and conflict between users, etc.
Effects of climate on highland zones
e Innorthern areas, temperature falls below freezing point/very cold in winter which:-
o Stops growth of trees
Makes farming impossible
o
Transhumance farming is also practiced
o o0 o0
Landslides and avalanches
People are forced to stay indoors so cottage industry is practiced
Effects of climate on lowland zones (semi —
arid) (Punjab, Sindh, etc.)
Crops can be grown in both summer and winter due to arid/hot summers and cool winters
e Densely populated due to extreme summer and winter temperature
e Monsoon rainfall suitable for Barani crops
e Monsoon rainfall provides enough water
to river/canals for irrigation
e Flooding in AFP and OFP which is dangerous
Effects of climate on arid zones
e Very hot in summer and dry (very low precipitation) so not ideal for cultivation
e ...and habitation
* Nomadic life...
e Karez system is practiced due to high evapotranspiration in Kharan desert
e People wear thick clothes to protect themselves from hot winds
e Frequent dust storms make work difficult
e Less drinking water
Hazards
Causes of floods
Natural
e Melting of snow in summer
e Heavy monsoon rainfall
Human
e Cutting of trees on foothills increases surface run — off
e Failure to strengthen or heighten embankments along river sides
e Lack of storage facilities e.g. dams and barrages
o Siltation is caused
Effects of flooding
Positive
e More fertility of land through fresh alluvium
e Floods also recharge ground water supply
e More fishin rivers/lakes
Negative
e Farmers cannot practice agriculture until water drains away
® Lossof lives
e Destruction of crops
e Loss of food supplies
e Mud houses and huts may be severely damaged
e Spread of water —born diseases e.g. cholera
e Roads and bridges wash away
® Loss of livestock
e Expensive to reconstruct the infrastructure e.g. roads, bridges, etc.
Precaution
e Planting trees on foothills to check the flow of running water
e Enlarging river channels so that they can hold more water
e Building embankments on river sides to reduce overflow
e Building reservoirs on rivers to store water
e Preventing building in areas where flooding is common e.g. AFP
e Publicizing flood warnings through media
e Timely evacuation of people from flooded areas
Droughts
Types
e Permanent: exists when crop cultivation is not possible e.g. Thal desert
e Seasonal: areas with well defined rainy and dry seasons e.g. Potowar Plateau
e Invisible: is the result of a water deficiency that reduces crop yield but is not severe enough to
destroy them
e Unpredictable: is the result of abnormally low rainfall in areas which have humid climates
Effects of drought
e Shortage of water
e Shortage of grazing grounds for livestock
e Crops may fail
e This may lead to food shortages
e More import of food like wheat
® Loss of lives due to starvation and thirst
® Loss of livestock
e Weak animals with low outputs
e Diseases e.g. of skin
e More rural
— urban migration
e May cause soil erosion through flooding
Solutions
® More reservoirs to store water
e Desalination of salty water
to increase the amount of fresh water for agriculture, etc.
* More plantations to reduce soil erosion
e ...and for more moisture in air for rainfall
