BPSC 71st CCE Prelims General Studies · Question 120 of 150

Correct — A, Subtropical Monsoon. Bihar lies entirely within the subtropical belt, north of the Tropic of Cancer, and its climate is the humid subtropical monsoon type — Cwa in the Köppen scheme, where C marks the mesothermal or warm-temperate group, w a dry winter and a a hot summer whose warmest month averages above 22 °C. Every element of the state's weather fits that label. The year runs in three clear parts: a hot, dry summer running from March into early June, with mean daily maxima climbing from about 32 °C in March to 37 °C in April and May; the south-west monsoon from about mid-June to the end of September, which delivers roughly four-fifths of the year's rain; and a cool, almost rainless winter. On the normals for the Bihar plain, July brings about 325 mm of rain and August about 276 mm, while November and December bring around 6 mm each — a wet-summer, dry-winter regime that is the definition of the monsoon type and the reason for the 'w' in Cwa. Annual rainfall averages roughly 1,200 mm, but it is very unevenly spread across the state, falling from over 1,800 mm at Kishanganj in the north-east to under 1,000 mm in Kaimur and Rohtas in the south-west, as the Bay of Bengal branch of the monsoon weakens westward. The temperature record is what fixes the word 'subtropical' rather than 'tropical': January on the plain averages a 24 °C day against a 9 °C night, a monthly mean near 16 °C, which is below the 18 °C floor that a Köppen tropical climate requires in every month of the year.

• (b)Tropical savannah — The serious rival, because savannah (Köppen Aw) shares Bihar's defining rhythm — a wet summer and a pronounced dry winter. The break comes on temperature, not rain. A tropical 'A' climate requires every month to average at least 18 °C, and Bihar's cold-season nights drop to 9–10 °C, pulling the January mean to about 16 °C. India's savannah belt lies in the peninsular interior south of the Tropic of Cancer; the whole of Bihar lies north of it.
• (c)Hot and dry — This describes the arid west — western Rajasthan and Kachchh, where annual rainfall falls below about 250 mm and evaporation exceeds it. Bihar receives roughly 1,200 mm and its recurring problem is the exact opposite of drought: the Ganga, Gandak, Bagmati and Kosi flood parts of the plain most years. A state that has to be embanked against its rivers cannot be classified hot and dry.
• (d)Hot and Semi Arid — Semi-arid (Köppen BSh) is the transition belt between the desert and the humid zone — interior Deccan, parts of Gujarat and southern Haryana — where rainfall runs a few hundred millimetres and is unreliable. Bihar's rainfall is four to five times that and is concentrated in a dependable monsoon season, so the state fails the aridity test on which the entire B group is defined.

The Köppen classification, which every Indian textbook uses behind the words in this question, sorts climates first by temperature and only then by rainfall, and remembering that order settles most exam items on the subject. The A group is tropical and is defined by the coldest month averaging at least 18 °C. The B group is dry and is defined by rainfall too low for the temperature, split into arid BW and semi-arid BS. The C group is warm-temperate or subtropical, with the coldest month between about 0 °C and 18 °C. Within a group the second letter reports the rainfall regime — w for a dry winter, s for a dry summer, f for rain through the year — and the third reports summer heat. Bihar comes out Cwa: warm-temperate, winter-dry, hot-summer, which is exactly what 'subtropical monsoon' means in plain English. The monsoon element is the seasonal reversal of winds: in summer the heated landmass draws moist air in from the ocean, and in winter the flow reverses off a cold continent, which is why the rain arrives in a single concentrated spell. Bihar's own geography then modulates it. The state covers 94,163 sq km at an average elevation of about 53 m, landlocked between Nepal, Jharkhand, West Bengal and Uttar Pradesh, and the Ganga splits it into North and South Bihar. The Bay of Bengal current of the monsoon enters from the east and loses moisture as it travels inland, which is why the north-east of the state is far wetter than the south-west.

Take the options in two passes and the question resolves without hesitation. The first pass is on rainfall. Options (c) 'Hot and dry' and (d) 'Hot and Semi Arid' both belong to Köppen's dry B group, which exists only where precipitation is too low for the temperature — under about 250 mm for the desert, a few hundred millimetres for the semi-arid belt. Bihar averages roughly 1,200 mm, and its permanent public problem is flood management on the Kosi, Gandak and Bagmati rather than drought. Both go, and half the paper's candidates have already secured the mark. The second pass is the hard one, between 'Subtropical Monsoon' and 'Tropical savannah', because both are wet-summer, dry-winter regimes and a candidate reasoning only from the rainfall graph cannot separate them. The discriminator is temperature: a tropical climate in the Köppen sense allows no month below an 18 °C mean, and Bihar's January runs near 16 °C, with minima of 9–10 °C on the plain. Anchor it geographically and it becomes unforgettable — the Tropic of Cancer passes through Jharkhand to Bihar's south and does not touch Bihar at all, so the state is subtropical by position as well as by thermometer. India's true savannah country lies in the peninsular interior, well south of that line.

• Bihar's climate is humid subtropical monsoon, Köppen Cwa — C for the warm-temperate group, w for a dry winter, a for a hot summer with the warmest month above 22 °C; the state lies wholly north of the Tropic of Cancer, which crosses Jharkhand to its south.
• Annual rainfall averages about 1,200 mm and roughly four-fifths of it falls in the south-west monsoon between mid-June and the end of September; on the plain's normals July brings about 325 mm and August about 276 mm against roughly 6 mm each in November and December.
• Rainfall declines sharply from north-east to south-west as the Bay of Bengal branch of the monsoon moves inland — over 1,800 mm at Kishanganj against under 1,000 mm in Kaimur and Rohtas, a near-doubling across a single state.
• The temperature test that excludes tropical savannah: a Köppen 'A' climate needs every month to average at least 18 °C, and January on the Bihar plain averages a 24 °C day against a 9 °C night — a monthly mean of about 16 °C, which places Bihar in the C group.
• Bihar covers 94,163 sq km at an average elevation of about 53 m, is landlocked by Nepal, Jharkhand, West Bengal and Uttar Pradesh, and is divided by the Ganga into North and South Bihar; the Gandak and Koshi rise in the Nepal Himalaya and the Bagmati in the Kathmandu valley, and together they flood parts of the plain most years.

• Reading 'monsoon' as automatically tropical — the monsoon rhythm describes the rainfall regime, while tropical versus subtropical is settled by the coldest month's temperature
• Choosing 'tropical savannah' because Bihar has a marked dry season; India's savannah belt lies in the peninsular interior south of the Tropic of Cancer, which does not cross Bihar at all
• Treating Bihar's rainfall as uniform — Kishanganj in the north-east receives more than 1,800 mm while Kaimur and Rohtas in the south-west receive under 1,000 mm, so 'most of Bihar' in the stem is doing real work

BPSC asks the state-level label directly — name Bihar's climate type, name its rainfall gradient, name the wettest district — and expects the textbook phrase rather than a Köppen code. UPSC almost never names a state: it hands you a set of characteristics, a temperature-and-rainfall table or a verbal description and asks which climate type they describe, or it tests one defining property in isolation, such as which regime is marked by a seasonal reversal of winds or by a definite wet and dry season. The BPSC form rewards the label; the UPSC form rewards knowing which single property defines each label.

• practice — not a real PYQ

  In the Köppen classification of climates, most of Bihar falls under which of the following types?

  • (a)Aw
  • (b)Cwa
  • (c)BSh
  • (d)Am

  Answer(b) Cwa — warm-temperate with a dry winter and a hot summer, the humid subtropical monsoon type. Aw is the tropical savannah of the peninsular interior, BSh the hot semi-arid belt, and Am the tropical monsoon type of the west coast and parts of the north-east.

• practice — not a real PYQ

  The average annual rainfall in Bihar generally decreases in which of the following directions?

  • (a)From north-east to south-west
  • (b)From south to north
  • (c)From west to east
  • (d)From north-west to south-east

  Answer(a) From north-east to south-west — Kishanganj in the north-east receives over 1,800 mm while Kaimur and Rohtas in the south-west receive under 1,000 mm, because the Bay of Bengal branch of the monsoon enters from the east and loses moisture as it moves inland.