Tarim Basin: desert and oases, oil and gas, and ecological protection

Desert and oases

A basin ringed by mountains

• The Tarim Basin is in southern Xinjiang, north-west China. It is China's largest inland basin: rivers flow in and never reach the sea.
• Mountains surround it: Tianshan (north), Kunlun (south) and Pamir (west). The east is open and low.

The Taklamakan Desert

• About 330,000 sq km, the largest desert in China and one of the largest shifting-sand deserts in the world.
• Why so dry? The mountains block moist winds, so rain is under 100 mm a year (some places under 50 mm), while evaporation is far higher.
• Large temperature changes: very hot days, cold nights; winters are freezing. Sand dunes move with the wind.

Oases

• An oasis is a green patch in a dry area where water is available.
• Rivers fed by snow and glacier melt come down the mountains. Where they reach the foothills, farms and towns appear in a ring around the desert (Kashgar, Hotan, Aksu, Korla).
• Crops: long-staple cotton, wheat, maize, and sweet fruit (grapes, melons, pears, apricots, jujube). Long hours of sunshine make the fruit sweet.
• The old Silk Road paths passed along these oases on the desert's edge.

The Tarim River (about 2,100 km) is China's longest inland river. It runs along the north edge of the desert and ends in the dry east.

Oil and gas

• Layers of rock under the Taklamakan hold large amounts of oil and natural gas. Drilling is hard because the wells are deep and the sand moves.
• The Tarim oilfield is one of China's big energy bases.
• A long pipeline (the West-East Gas Pipeline, about 4,000 km) carries gas from the basin to cities in the east such as Shanghai.
• A road, the Tarim Desert Highway (about 520 km), crosses the sand to serve the oil wells. Rows of grass and shrubs along it hold the sand and are watered by drip pipes.
• Good point: the gas can replace coal in cities and cut smoke. Careful point: drilling must not harm the fragile desert plants and water.

Ecological protection

The problem

• Farms and towns on the upper river took more and more water. The lower Tarim River dried for many years and a lake at its end shrank.
• Without river water, the desert poplars (a tough tree that holds sand) died, and sand began to spread.

Solutions

• Share water fairly: send planned amounts of water down the lower river, including from a big lake upstream.
• Save water: drip irrigation and covering fields with thin plastic sheets lose less water than flooding a field.
• Shelterbelts: rows of trees and shrubs around fields, roads and the desert edge slow the wind and fix the sand.
• Protect natural trees and limit new farmland; plant crops that need less water.

Rule to remember: take only as much river water as the whole river system can spare.

Try it: make an oasis

1. Fill a tray with dry sand. Mark mountains at one end with a book.
2. Pour a little "snowmelt" water near the book. Where does it spread?
3. Plant two cress seeds where the sand is wet. Which grows?
4. Now pour more water on one side only. Does the other side dry? This is the lower river problem.

Key formulas and definitions

• Inland basin: a low area ringed by mountains where rivers never reach the sea
• Taklamakan: about 330,000 sq km of moving sand; rain under 100 mm a year
• Oasis: a green patch in a dry area where water is available
• Tarim River: about 2,100 km, China's longest inland river
• Snowmelt: mountain snow and ice melting into rivers
• Drip irrigation: dripping water at plant roots to save water
• Shelterbelt: a row of trees or shrubs that slows wind and fixes sand

Worked examples

Common mistakes

• Thinking a desert has no water at all. Snowmelt rivers and oases exist at its edge.
• Thinking the Tarim River reaches the sea. It is an inland river that ends in dry land.
• Thinking more farms upstream never hurt anyone. They can dry the lower river.
• Thinking the Taklamakan is cold everywhere. It has hot days and cold nights, and its edges are fed by cold mountains.