Consider the following statements regarding ‘heat wave’ :
1. Heat wave is considered if the maximum temperature of a station reaches at least 30 °C or more for plains.
2. Heat wave is considered if th

Question

Consider the following statements regarding ‘heat wave’ :
1. Heat wave is considered if the maximum temperature of a station reaches at least 30 °C or more for plains.
2. Heat wave is considered if the maximum temperature of a station reaches at least 40 °C or more for hilly regions.
Which of the above statements is/are correct?

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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.

Why the other options are wrong — (a) 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) 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) 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.

Concept: 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.

State PCS 2023 Q82 — Geography PYQ with Answer

State PCS 2023 Q82 — Geography PYQ with Answer