Tuesday, 12 June 2012

Monsoons

Hello everyone!!! I suspect the nerves are starting to kick in so good luck to everyone doing the AQA A2 Unit 3 Geography exam! This is a rather late request from quite a few people so I thought I would quickly write it - last minute cramming always helps right.....

MONSOON = a large scale seasonal reversal in wind direction

This wind reversal is experienced in regions across the world but the most significant is the South East Asian Monsoon (this is our example of a climate in a tropical region) and is influenced by three main factors:-
1. Movement of the ITCZ - moves with regards to season as point of maximum insolation changes due to the 23.5 degree tilt of the Earth so ITCZ moves north of equator during northern hemisphere summer
2. Differential heating of land and sea which initiates pressure differences - land masses heat and cool quicker and to more extremes in relation to smaller heat changes over nearby seas; these differences are responsible for strength and direction of winds
3. Himalayas, which are high enough ot influence the general atmospheric circulation in the region

Summer: SW Monsoon = June - September
  • ITCZ dragged north
  • Low pressure over India
  • Land warmer than ocean
  • Coriolis deflects northerly winds to the east
  • Heavy rains move north along west and east coast
  • East rains deflected west due to Himalayas
  • Pattern of rainfall in summer monsoon is altered by topography. Western Ghats create rainshadow in central India, whilst Himalayas have same effect for central India
  • Some areas of SE India and Sri Lanka recieve rainfall in winter as winds pass over Bay of Bengal and gain moisture
Winter: NE Monsoon = October - May
  • ITCZ dragged south
  • High pressure over central Asia
  • Land cools rapidly
  • Coriolis deflects southerly winds to the west
  • Dry air dries further as it moves over Tibetan Plateau
  • Air warms as ut descends to the Indian Plains
- Monsoon in both retreat and arrival is stepped so Sri Lanka gets rainfall in early May whereas Pakistan in July. Retreat begins in September but does not reach Southern India until late November

Couple of facts.....
- 40C in May - average temperature is 30-35C year round
- 13000mm rain per year in Cherrapunji (well its spelt something like that!)
- 80% rain falls between June and September

Positives : )
- Very predictable!
- Relief from hot season as monsoon cools areas that reach 45C so cities have powershortages
- Reservoirs topped up
- Crop growth = stable diet is rice and Indian agriculture built around monsoons
- Monsoon clears out dust and pollution and rejunventates vegetation

Negatives : (
- Temperature restricts tourist season
- Droughts and issues with water supplies
- Flooding increases spread of water bourne diseases
- Restricts agricultural productivity
- 500 died in 1994 flash flood in Bangladesh

Monsoons and Global Climate Change
  • Half of global population rely on annual monsoon to bring water for agriculture
  • Variations of timing and intensity will affect billions of people
  • Frequency has increased 10% since 1950s and severe rains have doubled
  • Impacts of heavy rains i.e flash floods/landslides which then impact agriculture
  • Temperature increase of 3C means some areas get more rain, others droughts
  • Increase in malaria and cholera
Well I think that is about it for monsoons, well atleast I hope so as I don't think I really know anymore and the exam is tomorrow afternoon.

Good luck everyone!

P.S after unit 3 is out the way I will try and write some stuff for 4B at the weekend but remember all the skills stuff is already on here from January!

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