Climatology UPSC: Comprehensive Guide for UPSC Aspirants

• Climatology is the science of climate: the study of the long-term state of the atmosphere, its spatial patterns, the processes that produce them, and their changes and uses.
  • The word comes from the Greek klima (inclination, that is, of the Sun’s rays) and logos (study).
• It is the geographical sister of meteorology:
  • Meteorology explains the physics of the atmosphere and forecasts day-to-day weather.
  • Climatology generalises weather over decades and asks where and why climates differ.
• In Geography Optional, climatology forms a core unit of Paper I (Physical Geography). Its ideas run through the Indian climate and monsoon in Paper II and through environmental geography.

Weather and Climate

• Climate is therefore not just an average: it includes variability, seasonality and the frequency of extremes, such as cyclone tracks and drought return periods.

Elements of Weather and Climate

• Temperature
• Air pressure
• Wind (speed and direction)
• Humidity
• Clouds
• Precipitation
• Sunshine and solar radiation
• Visibility
• Pressure and wind act as the links: they move heat and moisture and so control the temperature and precipitation that define climatic types.

Controls of Climate

• Latitude: sets the angle of the Sun’s rays and day length, hence insolation. Temperature falls poleward, from the temperature belts of the torrid zone to the frigid zones.
• Altitude: temperature falls about 6.5 °C per km, so Shimla and Ooty are far cooler than the plains at their latitude.
• Distribution of land and water:
  • Water heats and cools slowly, so coasts have maritime climates and interiors continental ones.
  • Mumbai has a small annual range of temperature; Delhi has a large one.
• Ocean currents: warm currents warm the coasts they wash (north-west Europe), while cold currents chill them and create coastal deserts (Atacama, Namib).
• Pressure belts and winds:
  • Pressure belts and the planetary winds carry heat and moisture.
  • Onshore winds bring rain and offshore winds bring dryness.
• Mountain barriers:
  • The Himalaya shields India from Central Asian cold.
  • The Western Ghats produce heavy windward rain and a rain-shadow on the Deccan.
• Air masses, fronts and storms: cyclones and western disturbances bring much of the variability of weather.
• Local factors:
  • slope aspect
  • soil and vegetation
  • cities, which create heat islands

Branches and Scales

• Physical (thermal) climatology: energy and heat exchanges.
• Dynamic climatology: atmospheric motion and circulation.
• Synoptic climatology: weather types and pressure patterns.
• Regional climatology: classification and description of climatic regions.
• Applied climatology: climate for agriculture, health, buildings, cities.
• Palaeoclimatology: past climates.
• Scales:
  • microclimate: a field, street or slope
  • mesoclimate: a valley or city
  • macroclimate: a region or continent

The Climate System

• Climate is produced by the interaction of five components:
  • the atmosphere
  • the hydrosphere (oceans, lakes)
  • the cryosphere (ice and snow)
  • the lithosphere (land surface)
  • the biosphere (plants, animals, humans)
• Energy from the Sun drives the system; exchanges of heat, water and carbon among the components create feedbacks, which explain both variability (El Niño) and long-term climatic change.

The Climatology Unit at a Glance

• The UPSC syllabus lists:
  • temperature and pressure belts; heat budget; atmospheric circulation; stability and instability
  • planetary and local winds; monsoons and jet streams
  • air masses and frontogenesis; temperate and tropical cyclones
  • types and distribution of precipitation; weather and climate
  • Köppen’s, Thornthwaite’s and Trewartha’s classifications; hydrological cycle
  • global climatic change and the role and response of man; applied climatology and urban climate
• The topics below follow the logical order of study: energy → temperature → pressure and wind → moisture → disturbances → classification → change and application.

The Atmosphere and Its Energy

• Origin of the atmosphere:
  • The atmosphere evolved from a primordial hydrogen–helium envelope, through volcanic outgassing, to an oxygen-rich air built by photosynthesis.
• Composition and structure:
  • Nitrogen, oxygen, argon and the variable gases (water vapour, CO2, ozone) make up the air.
  • The atmosphere is layered into the troposphere, stratosphere, mesosphere and thermosphere.
• Heat budget:
  • Incoming insolation is balanced by outgoing terrestrial radiation in the heat budget of the Earth.
  • A tropical surplus and polar deficit drive the winds and ocean currents.
• Aurora: the polar lights mark the meeting of the solar wind with the upper atmosphere.

Temperature

• Temperature belts: world temperature depends on latitude, land and sea, currents and relief, shown by isotherms and annual ranges.
• Temperature inversion: layers where temperature rises with height trap fog, frost and smog.
• Stability and instability: comparing lapse rates decides whether air rises into clouds and storms or stays stable.

Pressure, Winds and Circulation

• Pressure belts: the pressure belts are the equatorial low, subtropical highs, subpolar lows and polar highs, which shift with the Sun.
• Forces and winds:
  • The pressure gradient, Coriolis force and friction shape the winds.
  • Winds are classed as planetary, periodic and local, such as the loo, foehn and mistral.
• General circulation: the Hadley, Ferrel and polar cells and Rossby waves move heat poleward.
• Jet streams: fast upper-air westerly and easterly jets steer storms and influence the monsoon.
• Monsoons:
  • Monsoons are explained by thermal, dynamic, jet-stream and ENSO theories.
  • The Indian monsoon is the classic case.

Moisture and Precipitation

• Humidity, evaporation and condensation: humidity is measured as absolute, relative or specific; condensation produces dew, frost, fog and clouds.
• Clouds: high, middle and low cloud types, and clouds of vertical development such as cumulonimbus.
• Precipitation:
  • Raindrops form by the Bergeron ice-crystal and collision–coalescence processes.
  • Rain is convectional, orographic or cyclonic, and its world distribution follows from these causes.
• Hydrological cycle: water circulates among ocean, air, land and ice.

Air Masses, Fronts and Storms

• Air masses: large bodies of uniform air, classified by their source regions (cP, mT and others) and modified as they travel.
• Fronts:
  • Fronts are the warm, cold, stationary and occluded boundaries between air masses.
  • Frontogenesis and frontolysis describe their birth and decay.
• Cyclones and anticyclones:
  • Low- and high-pressure systems have contrasting winds and weather.
  • The temperate cyclone forms on the polar front; the tropical cyclone draws on warm seas.
• Thunderstorms and tornadoes: convective storms pass through cumulus, mature and dissipating stages, and violent vortices form within them.

Classification of Climates

• Köppen: an empirical scheme based on vegetation, temperature and rainfall (A, B, C, D, E).
• Thornthwaite: a scheme based on precipitation effectiveness and potential evapotranspiration.
• Trewartha: a modified Köppen scheme that adds a subtropical group and highland climates.
• Climatic regions: the world’s climatic types, from equatorial to tundra, with their vegetation and economy.

Climatic Change and Applied Climatology

• Climatic change:
  • Evidence of past climates comes from ice cores, sediments, pollen and tree rings, through the Quaternary glaciations and the Little Ice Age.
  • Causes include orbital, solar, volcanic and tectonic factors, greenhouse gases and feedbacks.
• Role and response of man: greenhouse gases and aerosols drive present warming; the response runs through the UNFCCC, Paris and India’s NDCs and missions.
• Applied climatology and urban climate: climate is applied to agriculture, health, comfort and architecture; cities create heat islands, pollution domes and urban rainfall, met by heat action plans.