The tracking of a prehistoric river along the Thar can serve a fresh note on prospects of a similar dry-up in the future.
This week, an international journal brought out a study about a river that ran through northwest India’s Thar Desert 172,000 years ago before it dried up, ending its possible role as a lifeline to Palaeolithic populations in the subcontinent.
This extinct water-body, that meandered during the Old Stone Age along what is now Rajasthan, comes across as the oldest directly-dated phase of a river activity in Central Thar. The new findings, at a quarry in the village of Nal near Bikaner, are published in Quaternary Science Reviews. They predate any evidence for activity in modern river courses across the Thar Desert as well as the course of the intermittent Ghaggar-Hakra River (which flows in a part of India and Pakistan only during the monsoon).
The prehistoric river was active at a time when the monsoon was much weaker than it is in the region now, points out the study. That time, its people lived in a “distinctly different Thar Desert landscape than we encounter today”, adding, the river might have been “potentially an important corridor for migrations”.
Causes of disappearance
Rivers dry up for reasons ranging from just one to multiple reasons:
The dramatic alterations in climate, chiefly owing to a sustained rise in global temperature, augment evaporation of river water. Also, rainfalls become erratic and unpredictable, which in turn may lead to prolonged dry seasons. Glacier-fed rivers, over the decades, tend to shrink.
Spread of farms
Ever-increasing population warrants a consistent rise in the demand of food. As the need for farmlands increase, riverbanks turn more and more into agricultural fields. This also leads to higher consumption of river water for irrigation purposes.
Hydropower plants lead to building of dams down the course of rivers, checking the normal course of water-flow. Such electricity projects dry up downstream stretches of rivers, which has been the pattern across the world since the 20th century.
Sand found on river beds are half-processed and of high-quality. This has put the rivers in a dangerous state amid a flurry of construction in the modern era. Unregulated sand mining is altering the river bed, forcing a change in the course of flow, erosion of banks as well as sudden flooding. All these contribute to the eventual death of a river.
Cities expand often with bad planning, choking canals and channels leading to rivers, and drastically reducing their inflow. Coupled with massive industrialisation that requires factories to draw more water, a rising urban population adds to use of the resource. As the groundwater table falls, the volume of water in the adjacent rivers, too, goes down.
Mixture of challenges
Besides the above reasons, salinity, erosion, blue-green algal blooms, slump in the water quality and proliferation of invasive species can accentuate the death of a river.
Saraswati and others
India has for the past half a century been embroiled in a controversy about the reality of an ancient river that finds mentions in Hindu mythology. Whether the Saraswati upcountry actually flowed once upon a time has become a subject of animated discussions with political overtones since the 1970s. The debate apart, the river, linked to the Vedic Age, is widely believed to have disappeared around 4,200 years ago. The most-cited reasons include a disruption of the westerlies, coupled with a slump in the monsoons.
Contemporary studies hint also at the shrinkage of the Ganga, another major northern river, portending its disappearance in a distant future. This possibility applies to a clutch of other rivers in the upcountry, experts say.
The trend isn’t just Indian. In 2013, China said its 2011 census showed a decline of rivers to 22,909 from what was earlier estimated to be around 50,000. The sharp slump is partly attributed to “inflated figures” in past records, yet fact remains that the country is facing a major ecological issue.
Recent studies list quite a few rivers across the world that may disappear in 100 years. These include Los Angeles, Colorado (USA), Yellow (China), Indus (Afghanistan, Pakistan, China and India), Rio Grande (Mexico & America) and Murray (Australia), Teesta (India and Bangladesh), Niger (West Africa).
The results of disappearing rivers wouldn’t just be limited to water scarcity. The phenomenon can impact the world’s climate.
For instance, oceans could be saltier with lesser inflow of freshwater. This can alter temperature-driven ocean circulation patterns in ways that can be dangerous for human existence.
Desertification of lands is a recipe for famine compelling humans to migrate.
To prevent drying up of rivers and subsequent devastating consequences, experts have, from time to time, suggested several measures. Some of them are
- Map free-flowing rivers
- Ensure waters in rivers are in the right quantity, quality and that at the right time
- Reconsider current water-allocating policies
- Go for better management of water footprint across sectors – domestic, urban, agriculture, industrial and energy
- Incentivise good practices starting from the individual level: such as reuse and recycling water and dis-incentivise harmful ones such as pollution
Here’s a short documentary on the consequences of drying up of rivers: