Globally, free-flowing rivers, particularly those moving over a distance of more
than 1,000 Km are increasingly rare. Only 21 (12%) of the world’s 177 longest rivers run freely from source to sea, and the Salween is the last large free-flowing river in SE Asia. We know that free-flowing rivers provide water purification, sediment flux transportation and deposition, coastal and coral reef support, and cultural and aesthetic services which benefit people. Still, our understanding of the contributions they make to the global ecosystem is limited.
Two rivers whose natural flow has been interrupted over the millennia, are the Ganges and the Indus. Both depend on the Himalayan Glaciers for water and have supported millions of people and their livelihood over the ages. ( about 1/2 a Bil.in 2009)
Ganges Water suffers with Over-extraction, combined with climate change, this could spell disater for >200 Million people who depend on it ..
Ganges River Basin
Length: 2,507 Km
Basin size: 1,016,124 Km2
Population: roughly 200 million people Population density: average 401 people/ Km2 Key economic activity: agriculture
Key threats: water extraction, 14 proposed large dams since 2004. Other threat: climate change
Water withdrawal poses a serious threat to the Ganges. In India, barrages control all of the tributaries to the Ganges and divert roughly 60% of river flow to large scale irrigation . India controls the flow of the Ganges into Bangladesh
with over 30 upstream water diversions. The largest, the Farraka Barrage, 18 Km from the border of Bangladesh, reduced the average monthly discharge of the Ganges from 2,213 m3/s to a low of 316m3/s [14%]
The Indus is even more sensitive to climate change. The Himalayan glaciers provide the Indus with 70-80% of its water,the highest proportion of any river in Asia. This is double the proportion of water that they provide the Ganges (30%-40%).
Indus River Basin
Length: 2,900 Km Basin size: 1,081,718 Km2
Population: 178,483,470 people
Population density: 165 people/ Km2
Key economic activity: agriculture
Key threat: climate change
Other threats: water extraction, agricultural pollution, water infrastructure,
6 proposed large dams
The Indus river basin spans parts of four countries (Afghanistan, Pakistan, India and China) in an area that is more than 30% arid,and much drier than the nearby Ganges river basin.
The Indus River is critical for Pakistan’s 160 million people, and irrigates 80% of its 21.5 million ha of agricultural land.
The Indus River is extremely sensitive to climate change due to the high portion of its flow derived from glaciers. Temperature controls the rate of glacier melt, which in turn, provides more water in dry, warm years and less water in cool years. River catchments with a large portion of glacial melt water experience less variability in water flows. With climate warming, many glaciers will no longer exist to moderate the flow of these rivers. Thus communities which depend on glacier water will face more severe water shortages, variability and potentially greater flooding too.
The Indus basin is already suffering from severe water scarcity due to over extraction for agriculture, causing salt water intrusion in the delta. In 1995, the Indus River already supplied much less water per person than the minimum recommended by the United Nations and by 2025 is predicted to suffer even more severe water scarcity.
