By Sharat Karekaat*
All the great civilisations in the history of humankind have flourished alongside riverbanks. However, in recent years, India’s booming economy, rapid urbanisation and industrialisation have disturbed the ecology of our rivers. Divvying up the river water by building dams, diverting the flow of rivers for irrigation, deforestation, and exploitation of groundwater sources, has dramatically reduced the water flow in the rivers.
In a recent study, researchers from the Indian Institutes of Technology at Indore and Guwahati have uncovered how human activities affect the ability of river catchments to cope with climate change. The study, published in the journal Scientific Reports, has investigated the ability of these catchment areas to be resilient with disturbances in the natural water cycles. The team studied 55 catchment areas in peninsular India and found that more than 60% of them cannot cope with the changing climate, and may soon dry up.
Most rivers in peninsular India are rain-fed. The rainwater that discharges into the catchment areas feed these rivers. Besides, there is also a part of it that gets back into the atmosphere. “After falling on the ground, the rainwater gets divided into runoff and actual evapotranspiration—the amount of water that is transferred to the atmosphere via evaporation and transpiration”, notes Prof Manish Kumar Goyal from IIT Indore, who is an author of the study.
However, when a catchment becomes drier, a larger portion of the precipitation ends up as evapotranspiration, thus decreasing the runoff. River catchments can be affected by human activities and the changing climate. Unless rivers are resilient to these changes and bounce back to normal functioning, they get stuck in this cycle of becoming drier, eventually ebbing away.
The researchers of the current study analysed the influence of human activities and climate change on the resilience of 55 catchments areas from 17 river basins, including the Kaveri and Godavari. They examined the difference in the water that flows into a river (run-off) of these catchments between two periods to understand which of the two affect them more significantly. The first analysis was between 1988 and 1997 when there was less human activity in these regions, and again from 2001 to 2011, a period that witnessed a substantial rise in anthropogenic activities.
The researchers quantified the resilience of the river catchments in two ways. One, based on the deviation of the catchment’s response from its normal behaviour during the climate warming period. This period corresponds to the time where the annual temperature over India has increased by 0.22°C for every 10 years since 1971 compared to 0.05°C increase previously. The second approach was based on the catchment’s ability to maintain the partitioning between run-off water and evapotranspiration during the warming period in a way compatible with normal behaviour.
The results show that only 23 catchments are resilient to changes in climatic warming. Though none of them was seen to be completely resilient, more than 60% of those dominated by human settlements were not at all resilient. Almost all the catchments of river basins, like Baitarni, Brahmani, Godavari, Krishna, Mahi, Narmada, Sabarmati and Tapi, had a downward trend in their runoff generation.
“The annual runoff of many catchments have undergone downward trend, but their annual precipitations have shown an increasing rate, indicating that precipitation is not the sole reason for changes in the long-term runoff generation”, say the researchers.
On the contrary, around 60% of the catchments dominated by climatic changes are resilient, say the researchers. Most of these include regions from the eastern and upper southern part of India, whereas most of those in the western part were found to be non-resilient. All but ten catchments saw a decrease in the runoff generated during the period with increased human activities.
“Though the study considers climatic variability and human-induced distress on the catchment as independent of each other, the relationship between the two is very intricate and is never independent”, say the Prof Manish Kumar Goyal.
The researchers suggest that steps like planting grass, shrubs or trees to control soil erosion, water conservation techniques like roof water harvesting and harvesting ponds, and better management of forests are needed to mitigate the negative impact of human activities. “There should be guidelines to ensure sustainable extraction of water from rivers so that the rivers can maintain the flow that is key to sustain the aquatic ecosystem in it”, asserts Prof Goyal. In the next part of the study, the researchers hope to explore the influence of various human activities, such as pollution and deforestation of wetlands, on the catchment.