CDS (II) 2020 General Knowledge · Question 6 of 120

Correct — B, Leh. Leh is a cold desert. It sits at about 3,500 m on the Indus in Ladakh, behind the Greater Himalaya and the Zanskar range, so the south-west monsoon is wrung dry long before it can reach the valley. India Meteorological Department normals for the Leh station give roughly 35 mm of precipitation a year on fewer than four wet days; even the compilations that add the water equivalent of snow put the total near 100 mm. Jodhpur, the option most candidates reach for because the Thar is the obvious desert, records about 406 mm a year on the same kind of normals — more than ten times Leh's figure — because it still lies in the path of a weakened monsoon current. New Delhi and Bengaluru are wetter again.

• (a)Jodhpur — The tempting answer, because Jodhpur is the gateway to the Thar. But a hot desert on the monsoon's flank still collects about 406 mm a year, an order of magnitude more than Leh.
• (c)New Delhi — Delhi lies on the plain where the monsoon trough swings north, and receives several hundred millimetres in the season alone, plus a little winter rain from western disturbances.
• (d)Bengaluru — The wettest of the four. Bengaluru sits on the Deccan plateau and draws rain from both the south-west and the retreating north-east monsoon, which is why its rainfall is spread across a long season.

Rainfall in India is governed less by latitude than by position relative to moisture-bearing winds and to mountain barriers. Windward slopes are wet, leeward slopes and enclosed basins are dry. A cold desert like Ladakh is dry for the same reason as a hot desert, namely lack of moisture supply, but the cause is a rain shadow rather than subsiding high-pressure air, and the temperatures are freezing instead of scorching.

The trap is the word desert. Candidates map minimum rainfall onto the Thar and pick Jodhpur, which is genuinely arid but is not the driest place on the list. The way to reason it is to ask which of these four places the monsoon simply cannot reach. Delhi and Bengaluru are plainly in monsoon India; Jodhpur is on its dry margin; Leh is on the far side of two mountain systems from it. A useful cross-check is the vegetation: Ladakh supports almost no natural tree cover and its agriculture depends entirely on meltwater channels, which is not true of the Jodhpur countryside.

• India Meteorological Department normals for Leh, at 34 degrees 09 minutes North and 3,513 m above sea level, give about 35 mm of precipitation a year on about 3.8 wet days.
• Jodhpur's corresponding normals give about 406 mm a year on about 21 rainy days.
• Ladakh is a cold desert: dry because the Greater Himalaya and the Zanskar range block the monsoon, not because of subtropical high pressure.
• Farming in the Leh valley depends on glacier and snow meltwater led along channels, since precipitation alone cannot support a crop.
• Mawsynram and Cherrapunji in Meghalaya are at the other end of the Indian range, with annual totals of the order of 11,000 mm.

• Equating the word desert with the Thar and choosing Jodhpur.
• Assuming a place that is high and snowy must be wet. Snow on the ground says nothing about how much falls in a year.
• Forgetting that Bengaluru gets rain from the retreating monsoon as well as the south-west monsoon, so its season is long rather than short.

As a minimum or maximum rainfall comparison across four Indian cities, or as a reason question on why Ladakh is called a cold desert.

No directly related past PYQ was found.

• practice — not a real PYQ

  Ladakh is described as a cold desert mainly because of which one of the following?

  • (a)It lies within the subtropical high pressure belt
  • (b)It lies in the rain shadow of the Greater Himalaya and the Zanskar range
  • (c)Its soils cannot retain moisture
  • (d)It is too far from the sea for any winds to reach it

  Answer(b) It lies in the rain shadow of the Greater Himalaya and the Zanskar range — the monsoon current has lost its moisture on the southern slopes before it can cross into the Indus valley.

• practice — not a real PYQ

  Which one of the following pairs of places represents the two extremes of annual rainfall in India?

  • (a)Leh and Mawsynram
  • (b)Jodhpur and Chennai
  • (c)Shimla and Nagpur
  • (d)Amritsar and Bhopal

  Answer(a) Leh and Mawsynram — a few tens of millimetres a year in the Ladakh cold desert against totals of the order of 11,000 mm on the Meghalaya plateau.