Climate & Weather — Study Notes for UPSSSC PET

Overview

Climate and weather form a critical component of the Geography section in UPSSSC PET, with 3–5 direct questions typically appearing in the exam. Understanding the Indian monsoon system is particularly important since Uttar Pradesh's agriculture, water resources, and economy are directly tied to monsoon patterns. Beyond India, you must know the basic classification of world climate types and atmospheric phenomena like El Niño and La Niña that affect global weather patterns.

The key distinction to grasp: **weather** is the day-to-day atmospheric condition (temperature, humidity, rainfall on a given day), while **climate** is the average weather pattern over 30+ years for a region. Questions test your knowledge of monsoon mechanics, factors affecting Indian climate, major climatic zones in India and worldwide, and the impact of ocean-atmosphere interactions on weather.

Master the monsoon mechanism, Köppen climate classification basics, and the practical effects of El Niño/La Niña. These topics connect to agriculture, disasters, and current affairs, making them high-yield for PET preparation.

Key Concepts

• **Monsoon** derives from Arabic "mausim" (season); refers to seasonal reversal of wind direction. India receives 75–90% of annual rainfall during the southwest monsoon (June–September).

• **Indian climate is tropical monsoon type**, characterised by hot summers, moderate winters, and concentrated rainfall in 3–4 months. The Himalayas block cold Central Asian winds, while the Thar Desert creates low pressure attracting monsoon winds.

• **Four major seasons in India**: Winter (Jan–Feb), Pre-monsoon/Summer (Mar–May), Southwest Monsoon (Jun–Sep), Post-monsoon/Northeast Monsoon (Oct–Dec). Tamil Nadu receives most rain in the post-monsoon season.

• **Jet streams** are high-altitude westerly winds that influence monsoon onset and withdrawal. The subtropical westerly jet stream's northward shift in summer allows monsoon winds to enter India.

• **El Niño** is the warming of Pacific Ocean surface waters off South America, occurring every 2–7 years. It weakens the Indian monsoon, causing droughts. **La Niña** is the cooling phase, often bringing excess rainfall and floods to India.

• **Western Disturbances** are extratropical storms originating over the Mediterranean, bringing winter rainfall to North India (Punjab, Haryana, UP, Himalayas) — crucial for rabi crops.

• **Köppen Climate Classification** divides world climates into five major types: A (Tropical), B (Dry/Arid), C (Temperate), D (Continental), E (Polar). India has A, B, and C types across different regions.

• **Climatic regions of India**: Tropical wet (Western Ghats, Northeast), Tropical dry (Deccan interior), Semi-arid (Rajasthan fringe), Arid (Thar), Subtropical humid (Northern plains), Mountain climate (Himalayas).

Formulas / Key Facts

• **Southwest Monsoon period**: Early June to late September; accounts for 75% of India's annual rainfall.
• **Northeast Monsoon period**: October to December; Tamil Nadu receives 50–60% of its annual rain in this season.
• **Arabian Sea branch & Bay of Bengal branch**: The monsoon splits into two arms; Bay of Bengal branch is more powerful and brings heavy rain to Northeast and Eastern India first.
• **Normal monsoon onset date over Kerala**: June 1 (±7 days).
• **Mawsynram, Meghalaya**: Highest average annual rainfall in India (~11,872 mm) and world.
• **Western Disturbances**: Cause 15–20% of North India's annual rainfall, critical for wheat cultivation.
• **ITCZ (Inter-Tropical Convergence Zone)**: Low-pressure belt near the equator; its northward shift in summer draws monsoon winds into India.
• **Coriolis force**: Deflects winds; causes southwest direction of monsoon winds in Northern Hemisphere.
• **El Niño years in India**: 1987, 2002, 2009, 2015 saw drought or deficient monsoons.
• **La Niña correlation**: Often brings above-normal monsoon rainfall and cooler winters.
• **Tropical climate (Köppen A)**: Mean monthly temperature >18°C all year; found in peninsular India south of Tropic of Cancer.
• **Arid climate (Köppen B)**: Annual rainfall <25 cm; Jaisalmer, Barmer in Rajasthan.

Worked Examples

**Example 1: Monsoon Mechanism** *Question: Explain why the Indian monsoon reverses direction seasonally.*

**Solution:** In summer (April–May), intense heating of the Indian landmass creates a low-pressure area over North India. Simultaneously, the Indian Ocean remains relatively cooler, forming high pressure. Moisture-laden winds blow from high pressure (ocean) to low pressure (land), bringing the southwest monsoon.

In winter, the land cools rapidly, creating high pressure over Central Asia and North India. Winds reverse, blowing from land to sea (northeast monsoon). These are dry winds; only Tamil Nadu and adjoining areas receive rain due to picking up moisture while crossing the Bay of Bengal.

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**Example 2: El Niño Impact** *Question: How does El Niño affect Indian agriculture?*

**Solution:** El Niño warms the eastern equatorial Pacific Ocean, altering global atmospheric circulation. The Walker Circulation weakens, reducing moisture transport to the Indian subcontinent. This results in:

• Delayed monsoon onset or weak monsoon
• Below-normal rainfall (drought conditions)
• Reduced kharif crop yields (rice, cotton, sugarcane)
• Lower reservoir levels affecting rabi irrigation
• Increased food prices and rural distress

The 2015 El Niño caused two consecutive years of deficient monsoon, impacting GDP growth and farmer incomes.

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**Example 3: Climatic Region Identification** *Question: Which Köppen climate type is found in Rajasthan's Thar Desert?*

**Solution:** Rajasthan's Thar Desert falls under **Köppen BW (Arid Desert)** climate. Characteristics:

• Annual rainfall <25 cm
• High diurnal temperature range (hot days, cool nights)
• Sparse vegetation (xerophytic plants)
• Low humidity, high evaporation rates

Jaisalmer and Barmer districts are classic examples. The region experiences extreme summer temperatures (45–50°C) and mild winters.

Common Mistakes

• **Confusing weather and climate** → Weather is short-term (today's rain); climate is long-term average (monsoon pattern over decades). Exam questions use these terms precisely.

• **Thinking all of India gets monsoon rain simultaneously** → The monsoon progresses gradually. Kerala receives it first (June 1), North India by mid-June, and western Rajasthan last (mid-July). Know the progression pattern.

• **Mixing up El Niño and La Niña effects** → El Niño = warm Pacific waters = weak Indian monsoon = drought. La Niña = cool Pacific waters = strong monsoon = floods. They are opposite phenomena.

• **Ignoring the northeast monsoon** → Students focus only on southwest monsoon, but Tamil Nadu's main rainy season is October–December (northeast monsoon). This appears in questions about state-specific rainfall.

• **Assuming Western Disturbances bring summer rain** → Western Disturbances occur in winter (Dec–March) and are crucial for North India's rabi crops. They don't affect the summer monsoon.

Quick Reference

• **Indian monsoon = southwest (Jun–Sep) + northeast (Oct–Dec); 75% rainfall in SW monsoon.**
• **Mawsynram (Meghalaya) = wettest place in India; Jaisalmer (Rajasthan) = driest.**
• **El Niño = Pacific warming = Indian drought; La Niña = Pacific cooling = excess rain.**
• **Western Disturbances = winter extratropical storms = North India winter rain.**
• **ITCZ northward shift in summer = pulls monsoon winds into India.**
• **Köppen A (Tropical) = South India; B (Arid) = Rajasthan; C (Temperate) = Hills.**