BPSC 69th CCE Prelims General Studies · Question 82 of 144

Correct — D, Neither 1 nor 2. Both numbers in the stem are genuine India Meteorological Department figures, but they have been attached to the wrong terrain. IMD's Weather FAQ answers 'What is heat wave?' with a definition and then a rule: the definition is 'a continuous spell of abnormally hot weather', and the rule is that 'Heat wave need not be considered till maximum temperature of a station reaches at least 40º C for Plains and at least 30º C for Hilly regions.' NDMA's heat-wave page reproduces the same criteria word for word, prefacing them with its own description of the phenomenon as 'a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India', typically between March and June. So the plains threshold is 40 °C, not the 30 °C of statement 1, and the hill threshold is 30 °C, not the 40 °C of statement 2 — the two have simply been exchanged, which makes both statements false and (d) the answer. It is worth seeing what the threshold actually does, because that is the part a summary usually drops: it is only a floor, a temperature below which IMD will not even begin to consider a heat wave. The declaration itself then rests on departure from the station's own normal. Where the normal maximum is 40 °C or below, a departure of 5 to 6 °C is a heat wave and 7 °C or more a severe heat wave; where the normal maximum is above 40 °C the bands tighten to 4 to 5 °C and 6 °C or more. Above all of this sits an absolute override: 'When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave should be declared.' And because heat is an area phenomenon rather than a station one, the FAQ adds that 'Heat wave/ Cold Wave and hot Day/ Cold Day are area specific phenomena. Therefore they may be described for a Met. Sub-division or a part thereof, when at least two stations satisfy the criteria.' Note also what the source does not contain. The FAQ writes special criteria for coastal stations only under cold wave and cold day, where the 10 °C minimum-temperature threshold is rarely reached and a wind chill temperature is substituted; there is no coastal heat-wave threshold in it at all, and none on NDMA's page either. The heat-wave rule as published is binary — plains and hills — which is exactly the pair the stem has inverted.

• (a)Both 1 and 2 — This accepts both halves of the swap at once. It would mean IMD calls 30 °C a heat wave on the Gangetic plain, where a Bihar station is already past 30 °C on ordinary March afternoons and would therefore be under a standing heat-wave declaration for most of the hot-weather season, and simultaneously refuses to call one in the hills until 40 °C. Two rules that between them would flood the plains with false alarms and silence the hills entirely cannot both be the published criteria of a working forecasting agency.
• (b)Only 1 — Keeps the plains figure at 30 °C and correctly rejects the hill figure, so this is the answer of a candidate who has spotted half the swap. But 30 °C is the hill-station threshold: on the plains a station has to reach at least 40 °C before IMD will consider a heat wave at all, and even then it must run 5 to 6 °C above its own normal, or hit 45 °C outright. Bihar's plains cross 30 °C by early March without any heat warning being issued, which is the everyday observation that disproves statement 1.
• (c)Only 2 — Keeps the hill figure at 40 °C. This is the self-defeating half of the swap: hill stations such as Shimla or Ranikhet seldom or never record 40 °C, so on this reading they could not register a heat wave in any year, and IMD's separate 30 °C hill threshold would have no work to do. A criterion that can never be met is not a criterion, and that test alone is enough to reject statement 2 without recalling either number.

The India Meteorological Department, founded in 1875 and now under the Ministry of Earth Sciences, is the authority that defines and declares India's extreme-temperature events, and its definitions are numerical rather than descriptive. A heat wave in IMD's scheme has two limbs. The first is an absolute floor that varies with terrain — at least 40 °C for the plains and at least 30 °C for hilly regions — below which no heat wave is considered however unusual the reading. The second is a departure test measured against that station's own normal maximum, with a straight override at an actual maximum of 45 °C. The same architecture governs the mirror events, and seeing the whole family at once is what makes the heat-wave numbers stick. A cold wave is defined as 'a rapid fall in temperature within 24 hours to a level requiring substantially increased protection to agriculture, industry, commerce, and social activities', and is then pegged to departure from the normal MINIMUM: -5 to -6 °C where the normal minimum is 10 °C or more, -4 to -5 °C where it is below 10 °C, with a cold wave declared outright when the wind chill temperature WCTn falls to 0 °C or less. For coastal stations, where a 10 °C minimum is rarely reached, IMD substitutes that wind chill temperature and allows a 'cold day' on a minimum-temperature departure of -5 °C or less irrespective of the 10 °C threshold, with cold wave taking priority if both criteria are met. The 'hot day' concept was added for a situation the wave criteria miss: in the northern plains, dust in suspension keeps minimum temperatures far above normal while maxima stay near normal, so nights never cool. IMD's rule is 'whenever, the maximum temperature remains 40ºC or more and minimum temperature is 5º C or more above normal'. Every one of these is a two-part test — a floor plus a departure — and the floor is the part that changes with terrain.

The reliable way through a swapped-pair question is to test each number for physical sense rather than to hunt for the memory. Hill stations are cooler than plains stations by definition, so whatever thresholds exist, the hill figure has to be the lower of the two. Statement 2 asks a hill station to reach 40 °C, a temperature many of them have never recorded, which would make heat waves impossible in the hills; that alone tells you the pair is inverted, and once inverted statement 1 falls with it. Notice that this reasoning needs no memorised number — it needs only the direction of the inequality, which is why it survives exam pressure better than recall does. The second discriminating point is that the threshold is a floor, not the definition. A Bihar plains station crossing 40 °C is not automatically in a heat wave: it must also run 5 to 6 °C above its own normal, or hit 45 °C outright, and a second station in the same meteorological sub-division must satisfy the criteria before IMD describes a heat wave for the area. That departure-from-normal design is also why a heat wave is not the same thing as the hottest day of the year — a station whose normal maximum is already very high needs a smaller excursion (4 to 5 °C) than a station whose normal is moderate (5 to 6 °C), because the criterion measures abnormality, not heat. Note finally the exam-craft signal: when a two-statement question offers mirror-image figures for two categories, 'Neither 1 nor 2' is a live answer far more often than candidates assume, because inverting a real pair is the cheapest way for a setter to build two false statements out of one true fact — and a candidate who half-remembers the fact is more likely to be trapped than one who never learnt it.

• IMD's Weather FAQ defines a heat wave as 'a continuous spell of abnormally hot weather' and states, verbatim: 'Heat wave need not be considered till maximum temperature of a station reaches at least 40º C for Plains and at least 30º C for Hilly regions' — NDMA's heat-wave page reproduces the same criteria
• NDMA describes a heat wave as 'a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India', typically between March and June and in rare cases extending into July
• Where a station's normal maximum temperature is 40 °C or less, IMD calls a heat wave on a departure from normal of 5 to 6 °C, and a severe heat wave at 7 °C or more
• Where the normal maximum exceeds 40 °C the bands narrow to a departure of 4 to 5 °C for a heat wave and 6 °C or more for a severe heat wave
• Regardless of the normal, 'when actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave should be declared'
• Heat wave, cold wave, hot day and cold day are area-specific phenomena: IMD describes them for a meteorological sub-division or a part of one when at least two stations satisfy the criteria
• The 'hot day' criterion covers the dust-laden northern-plains spell in which nights fail to cool: 'whenever, the maximum temperature remains 40ºC or more and minimum temperature is 5º C or more above normal'
• The cold wave rule is built the same way but on minimum temperature: where a station's normal minimum is 10 °C or more, a departure of -5 to -6 °C is a cold wave and -7 °C or less a severe cold wave; below a 10 °C normal minimum the bands are -4 to -5 °C and -6 °C or less, and a cold wave is declared outright when the wind chill temperature WCTn is 0 °C or less
• IMD's FAQ writes coastal-station criteria only for cold wave and cold day, substituting the wind chill temperature for the rarely-reached 10 °C minimum; it prescribes no coastal heat-wave threshold, and neither does NDMA's page — the published heat-wave rule is plains-versus-hills only

• Recalling the two numbers correctly but attaching each to the wrong terrain — exactly the swap this question is built on
• Believing a single station crossing the threshold triggers a declaration; IMD needs at least two stations in a meteorological sub-division
• Treating the 40 °C plains figure as the definition of a heat wave rather than as the floor below which one is not even considered — the declaration turns on departure from that station's own normal

BPSC takes a published numerical criterion from a Government of India agency, splits it into two mirror statements and inverts them, so the mark depends on having read the definition at source rather than in a summary — and the correct response is often the 'neither' option, which candidates under-select. UPSC approaches heat from the consequence end: wet-bulb temperature and the failure of perspiration, or what the absence of the Himalayas would do to India's cold waves. The same syllabus line is therefore tested as a threshold table by BPSC and as physiology and climatology by UPSC, and the IMD FAQ is the single document that serves both.

No directly related past PYQ was found.

• practice — not a real PYQ

  According to IMD, a heat wave is declared irrespective of a station's normal maximum temperature when its actual maximum temperature remains at least

  • (a)40 °C
  • (b)42 °C
  • (c)45 °C
  • (d)47 °C

  Answer(c) 45 °C — IMD's criterion is that 'when actual maximum temperature remains 45 °C or more irrespective of normal maximum temperature, heat wave should be declared'.

• practice — not a real PYQ

  IMD describes a heat wave for a meteorological sub-division only when the criteria are satisfied at a minimum of how many stations?

  • (a)One
  • (b)Two
  • (c)Three
  • (d)All stations in the sub-division

  Answer(b) Two — heat wave and cold wave are area-specific phenomena and IMD describes them for a sub-division, or part of one, when at least two stations satisfy the criteria.