UPSC Mains 2026 GS1 Q14: model answer
Compare the Loo, Chinook and Foehn winds with respect to their regions of prevalence, their nature and climatic impacts.
What the question wants
A three-way comparison on region, origin/nature, and impact. A table fits well.
How to structure it
Intro: local winds. Body: comparison table plus short notes on mechanism. Conclusion: relevance (heatwaves, snowmelt).
- 1Comparison table plus short notes on mechanism
Model answer
Local winds arise from regional pressure differences and relief. The Loo is a hot continental wind; the Chinook and Foehn are warm, dry winds created when air descends the leeward side of mountains.
- 1Moist air rises on windward slope
- 2Cools, condenses, rains
- 3Crosses the crest dry
- 4Descends and warms at the dry rate
- 5Arrives warm and dry in the valley
| Feature | Loo | Chinook | Foehn |
|---|---|---|---|
| Region | North and north-west India, Pakistan plains | East slopes of the Rockies, USA and Canada | North slopes of the Alps, Switzerland and Austria |
| Season | May–June afternoons | Winter and early spring | Spring mostly |
| Origin | Heating of the land under clear skies, westerly flow from Thar | Pacific air rises, cools, drops moisture, then descends | Same mechanism over the Alps |
| Nature | Hot, very dry, dusty, 45°C+ | Warm, dry, sudden temperature rise | Warm, dry, gusty |
Mechanism of Chinook and Foehn: rising air cools at the wet adiabatic rate after condensation; descending air warms at the faster dry rate. So it reaches the valley warmer and drier than it started.
Climatic impacts
- Loo: heatstroke deaths, drying of crops and water bodies, power demand peaks.
- Chinook ('snow eater'): melts snow quickly, opens pastures for cattle, but can cause avalanches and fire risk.
- Foehn: ripens grapes and melts snow, but raises forest fire and avalanche risk.
With rising heatwaves, Loo days are lengthening. IMD's heat action plans, first tried in Ahmedabad (2013), are the practical response.
Keywords, cases and data to drop in
adiabatic warming leeward side snow eater heat action plan
Where most answers lose marks
- No table or structured comparison
- Mixing up Chinook and Foehn regions
Same theme in Prelims
Which of the following are the evidences of the phenomenon of continental drift?
- I. The belt of ancient rocks from Brazil coast matches with those from Western Africa.
- II. The gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side.
- III. The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere.
Select the correct answer using the code given below.
Answer (c) & explanation
All three are evidence for continental drift (c). Item I is right: the belt of ancient rocks on the coast of Brazil matches those of West Africa. Item II is right: Ghana's gold has no source rock in Ghana, but its source exists in the Brazil plateau, showing the two lands once lay side by side. Item III is right: India's Gondwana sediments have twins in six southern landmasses. So options (a), (b) and (d), which leave items out, fail.
Notice other proofs used by Alfred Wegener (1912): the "jig-saw fit" of coastlines, tillite from old glaciers, and fossils like Mesosaurus found on both sides of the Atlantic. His idea was later explained by sea-floor spreading and plate tectonics.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement I : The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions.
Statement II : Subtropical and temperate areas have less dry winds.
Which one of the following is correct in respect of the above statements?
Answer (c) & explanation
Statement I is correct, Statement II is wrong (c). Statement I is right: dust in the air is highest over the subtropical and temperate belts. Statement II is wrong, because it reverses the reason: these belts have more dry winds, not fewer, and those winds lift dust from deserts and dry land, such as the Sahara, Thar and Gobi. Near the equator, heavy rain washes dust out of the air, and in polar regions, ice and snow give little dust to lift. So options (a), (b) and (d) fail.
Notice why dust matters: it acts as hygroscopic nuclei around which water condenses into clouds and rain. It also scatters sunlight, giving red sunrises and sunsets. Saharan dust even feeds the Amazon with phosphorus.
Answer as per the official UPSC answer key.
Consider the following statements :
Statement I : In January, in the Northern Hemisphere, the isotherms bend equatorward while crossing the landmasses, and poleward while crossing the oceans.
Statement II : In January, the air over the oceans is warmer than that over the landmasses in the Northern Hemisphere.
Which one of the following is correct in respect of the above statements?
Answer (a) & explanation
Both are correct and Statement II explains Statement I (a). Statement II is right: in the northern winter (January), land loses heat fast, while the oceans stay warmer, because water heats and cools slowly. Statement I follows: a given temperature line, or isotherm, is pushed south (equatorward) over the cold land and north (poleward) over the warm ocean. Options (b), (c) and (d) miss this link.
Notice the reverse in July: land is hotter, so isotherms bend poleward over land. Warm currents like the Gulf Stream and North Atlantic Drift push isotherms further north, keeping Norway's ports ice-free. In the Southern Hemisphere, with more ocean, isotherms run fairly straight.
Answer as per the official UPSC answer key.
Learn the concept
Question text as printed in the official UPSC question paper: https://www.upsc.gov.in/sites/default/files/QP-CSM-26-010926-GENERAL%20STUDIES%20PAPER%20-%20I.pdf The model answer is original Battle IAS work; use it to learn structure, not to memorise.