Climate & Weather

Learning Objective: Distinguish between weather and climate and explain Nepal's climate zones

Why Kathmandu Feels Different from Biratnagar

If you have traveled from the Terai to Kathmandu -- or from Kathmandu to Namche Bazaar -- you have experienced Nepal's extraordinary climate diversity firsthand. In a single day of driving, you can move from tropical heat to alpine cold. This is because Nepal, despite its small size, spans a vast range of elevations, creating climate zones found nowhere else within such a compact area.

Weather vs. Climate

These two terms are often confused:

• Weather is the day-to-day condition of the atmosphere at a specific place and time (e.g., "It is raining in Pokhara today").
• Climate is the average weather pattern of an area over a long period, usually 30 years or more (e.g., "Pokhara has a subtropical climate with heavy monsoon rainfall").

A simple way to remember: weather is what you wear today; climate is what clothes are in your wardrobe.

Layers of the Atmosphere

The Earth's atmosphere has five main layers:

1. Troposphere (0--12 km) -- where all weather occurs; temperature decreases with altitude
2. Stratosphere (12--50 km) -- contains the ozone layer that protects us from UV radiation
3. Mesosphere (50--80 km) -- where meteors burn up
4. Thermosphere (80--700 km) -- extremely hot, where auroras occur
5. Exosphere (700+ km) -- the outermost layer, transitioning into space

Elements of Weather

Weather is determined by several measurable factors:

• Temperature -- how hot or cold the air is
• Precipitation -- rain, snow, sleet, or hail
• Humidity -- the amount of moisture in the air
• Air pressure -- the weight of the atmosphere; changes in pressure cause wind
• Wind -- the horizontal movement of air from high-pressure to low-pressure areas

Nepal's Climate Zones

Nepal's dramatic elevation change -- from 60 meters in the Terai to 8,849 meters at Sagarmatha -- creates five distinct climate zones within a horizontal distance of less than 200 km:

1. Tropical Zone (below 1,000 m) -- The Terai and lower Siwalik hills. Hot summers (up to 45 degrees Celsius in places like Nepalgunj), mild winters. Heavy monsoon rainfall. This is Nepal's rice-growing belt.

2. Subtropical Zone (1,000--2,000 m) -- Middle hills, including Kathmandu Valley (1,350 m). Pleasant temperatures, moderate rainfall. Kathmandu's average annual temperature is about 18 degrees Celsius.

3. Temperate Zone (2,000--3,000 m) -- Upper hills and lower mountains. Cool temperatures, forests of oak and rhododendron (Nepal's national flower).

4. Subalpine/Alpine Zone (3,000--5,000 m) -- Sparse vegetation, cold winters, snow. Home to yak herders and communities like the Sherpas of Solukhumbu.

5. Arctic/Nival Zone (above 5,000 m) -- Perpetual snow and ice. No permanent human settlement. Includes the world's highest peaks.

The Monsoon: Nepal's Lifeline

The South Asian monsoon dominates Nepal's climate. From June to September, moisture-laden winds from the Bay of Bengal bring approximately 80% of Nepal's annual rainfall. Agriculture, hydropower, and water supply all depend on the monsoon. Too little rain causes drought; too much causes devastating floods and landslides -- both increasingly common due to climate change.

Nepal is one of the world's most vulnerable countries to climate change. Glacial lakes in the Himalayas are expanding due to melting glaciers, creating the risk of Glacial Lake Outburst Floods (GLOFs).

Think Critically

Nepal contributes less than 0.1% of global greenhouse gas emissions, yet it faces some of the worst impacts of climate change. Is this fair? What should Nepal's approach be in international climate negotiations?

Summary

• Weather is short-term atmospheric conditions; climate is the long-term average.
• The atmosphere has five layers, with all weather occurring in the troposphere.
• Nepal has five climate zones -- from tropical to arctic -- due to its extreme elevation range.
• The monsoon (June--September) provides 80% of Nepal's annual rainfall.
• Nepal is highly vulnerable to climate change, facing risks like GLOFs and changing monsoon patterns.