Winter rainfall received by the Mediterranean region is the result of

Question

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Correct — option (2). The Mediterranean climate is defined by an inversion that Indian candidates find counter-intuitive: the summer is the dry season and the rain comes in winter. The cause is the seasonal migration of the global pressure and wind belts, which follow the apparent movement of the overhead sun north and south through the year. In the northern summer the belts shift northward, and the sub-tropical high pressure belt comes to lie over the Mediterranean basin. Air in a high pressure cell subsides, warms as it descends and diverges at the surface, and subsiding warm air is the enemy of condensation, so the summer there is hot, cloudless and rainless. In the northern winter the sun moves south and the whole system of belts moves south with it. The sub-tropical high withdraws off the basin, and the Mediterranean is left under the belt of the westerlies and the low pressure conditions that travel with them, along which temperate cyclones move eastward across the sea bringing cloud, wind and rain. The winter rainfall is therefore the direct result of a low pressure regime coming to sit over the region, and that regime arrives because the belts have shifted. That is precisely the sentence printed as option (2), which states both the shift and what the shift brings, and it is why option (2) rather than option (1) is the answer even though option (1) is not false. The stem asks what the winter rainfall is the RESULT of, and a result has to be traced to the condition that produces it. A shift of pressure belts happens at every longitude on the Earth and produces summer rain at some latitudes, winter rain at others and permanent drought at others still; naming the shift alone does not say which. Option (2) closes the chain by naming the condition the shift creates over this particular region, and that condition is what actually delivers the rain.

Why the other options are wrong — (a) This option is true as far as it goes, and that is exactly what makes it dangerous: it names the mechanism and then stops before the mechanism does any work. The seasonal migration of the pressure belts is a global phenomenon and its consequences differ entirely with latitude — it gives the savanna lands their summer rain, leaves the hot deserts under permanent high pressure, and gives the Mediterranean lands their winter rain. To say that the winter rainfall results from the shifting of pressure belts is to give the cause of the cause while leaving out the condition that actually produces rain, namely the low pressure and the travelling depressions that occupy the basin once the sub-tropical high has moved away. Options (1) and (2) are nested, the second containing the first, and when an option set is built that way the shorter member is generally placed there to collect a candidate who recognises a familiar phrase and stops reading.  (c) This describes a source of moisture rather than a cause of a season, and it fails a test that is worth applying to every explanation of a seasonal pattern: a factor that does not change with the season cannot explain something that does. The Mediterranean Sea lies where it is all year round, so onshore flow across it, by itself, cannot account for rain in December and drought in July. What changes between the two seasons is the pressure regime overhead, and it is that change which decides whether air rises and condenses or subsides and dries. There is a grain of truth buried in the option, since the westerlies of winter do cross the sea and pick up moisture from it, and that moisture is what falls as rain; but the sea supplies the water, while the shift of the belts supplies the lift, and the stem is asking for the cause of the regime, not the origin of the vapour.  (d) The Alps lie to the north of the Mediterranean basin, so orographic rainfall on their windward slopes is rain that falls on the mountains rather than on the Mediterranean lands whose climate the question is about. The option also fails the same seasonal test as option (3): a mountain range is a permanent feature and cannot by itself create a rainfall maximum in one season and a drought in the other. Relief genuinely does shape how much rain a place receives, since a moist wind forced to rise will cool and condense, and within the Mediterranean region the totals vary sharply between windward and leeward slopes for exactly that reason. But relief can only modify a rainfall that is already being delivered by the wind system, and the question is about why the rain-bearing wind system is present in winter and absent in summer.

Concept: The Earth carries a set of latitudinal pressure belts — the equatorial low, the sub-tropical highs near 30 degrees, the sub-polar lows near 60 degrees and the polar highs — and between them lie the planetary winds, the trades, the westerlies and the polar easterlies. These belts are not fixed. They migrate north and south with the apparent movement of the overhead sun, and the migration is what gives most of the world's climates their seasonal rhythm. Places that stay within one belt all year have a uniform regime: the equatorial belt has rain throughout the year, and the hot deserts, sitting permanently beneath the sub-tropical high, have almost none. Places that lie at the boundary of two belts pass alternately under each, and take their seasons from that alternation. The savanna lands swing between the equatorial low in the high-sun season, which brings rain, and the trade winds in the low-sun season, which bring drought. The Mediterranean lands do the opposite: they lie between the sub-tropical high and the westerlies, so they get the high pressure and its drought in summer and the westerlies with their travelling depressions, and therefore their rain, in winter. This is why the Mediterranean type is found only on the western margins of continents between roughly 30 and 40 degrees of latitude, and why it recurs so far from the Mediterranean itself — in central California, central Chile, the Cape region of South Africa, and southern and south-western Australia.

State PCS 2023 Q28 — Geography PYQ with Answer

State PCS 2023 Q28 — Geography PYQ with Answer