Most of the Bihar comes under which of the following climate type?

Question

UnlockIAS · Accepted Answer

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.

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

Concept: 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.

State PCS 2025 Q120 — Geography PYQ with Answer

State PCS 2025 Q120 — Geography PYQ with Answer