Welcome to SNM IAS Academy for IAS Coaching in Chandigarh. Check out the Knowledge Center for latest Blogs, Articles and Current Affairs Tests

  • Call

    0172-4665252
  • Email

    snmeducation2011@gmail.com

29 January – GROWING IMPACT OF CLIMATE CHANGE: LOWERWATER LEVELS IN HIMALAYAN RIVER BASINS

Rising temperatures are changing the water cycle, scientists have found, with less water being stored in crucial river basins

As the world warms, less water is replenishing major river basins, a new study has found. This could impact water availability, with big implications for future water security.

The river basins of the Himalayas are among those experiencing the largest changes.

Water availability depends on how much water is stored on the surface or underground in lakes, rivers and groundwater, including soil moisture, snow and ice. The movement of water into these catchment areas is called ‘water recharge’.

But rising temperatures mean more water is being lost through evaporation and absorbed by plants. At the same time, less water is entering river basins from rain and snowfall as weather patterns change.

The result is lower levels of water in the basins, a trend which is expected to continue with the growing impact of climate change.

Climate change worsens water crisis in Indus-Ganga-Brahmaputra basins.

Spring-fed rivers in the Indian Himalayas drying up.

The researchers from the Indian Institute of Science and the University of New South Wales in Australia studied 31 river basins.

They calculated that the replenishment of the Irrawaddy basin fell by 39% with each degree rise in temperature, the Indus by 24%, Mekong by 15% and Ganga-Brahmaputra by 14%.

15 of the 31 river basins assessed in global study of the impact of rising temperatures on water recharge.

For 23 of the 31 river basins, the researchers found a decrease in recharge corresponded to an increase in temperature.



METHODOLOGY



CALCULATING WATER RECHARGE

To analyse the effect of temperature on water recharge, the researchers used satellite data to work out “terrestrial water recharge” (TWR) – the total amount of water entering all surface and subsurface storages annually. Taking into account various rates of rain and snowfall (precipitation) in different areas, the researchers then calculated the “relative recharge” rates. They studied data between April 2002 and January 2017, comparing the relative recharge of each basin with the annual temperature.

Basins with distinct seasonal dry and wet cycles were selected, as they had clear high and low water recharge periods. For example, in India in the Ganga-Brahmaputra river basin, the dry season is between March and May, and the wet season is from June to September – when the basin is recharged.

In areas that predominantly have snowfall, recharge occurs in the winter months.

Glacial lakes become more deadly as Himalayan ice melts.



A WARNING FOR SOUTH ASIA

These calculations are a cautionary message for South Asia because use of water is high and increasing due to agriculture and urbanisation.

South Asian rivers depend on monsoon rainfall and it is uncertain how climate change will affect monsoon rainfall patterns.

But this study shows, quite simply, that in a hotter climate more water will be lost to evaporation and less will be left to replenish rivers, lakes and underground water.

India, Pakistan and Bangladesh, together with north China, account for more than half of the world’s annual use of groundwater.

 The recharging of water in these countries’ river basins is crucial for agriculture, regional economies and development.

The Indus and Ganga-Brahmaputra basins support two of the world’s largest agricultural regions, but are already experiencing high groundwater stress.

In the Indian state of Uttar Pradesh, in the Ganga basin, more than 70% of its replenishable groundwater has been extracted to date, as the state is densely populated and intensely farmed.

Similarly Indian Punjab, in the Indus basin, extracts more than 150% of its replenishable groundwater.

Water-thirsty crops  have been grown in these river basins, which will be affected by the warming-induced decline in recharge predicted by this study.

Rice is one of these thirsty crops. The world’s major rice-growing areas are in Asian river basins, including the Irrawaddy basin, most of which lies in Myanmar.

Groundwater irrigation is becoming important in the lower Irrawaddy basin, especially for growing dry-season crops. Lower recharge rates in the basin could be a cause for concern.

Groundwater recharge rates in the dry zone of central Myanmar are lower than other parts of the basin. More than 10 million people live in the country’s most water-stressed region.



IMPENDING URBAN CRISIS

Analysis of water recharge data is important for developing sustainable groundwater management policies.

It is very important for Indian cities, which overwhelmingly depend on groundwater for meeting their needs – this study shows climate change may affect natural recharge processes.

A recent WWF report identified about 80 Asian cities, including 30 in India, as facing severe water scarcity by 2050. Kolkata, in the Ganga-Brahmaputra basin, is one of the cities at high risk.

Kolkata, surrounded by the Ganga on one side and containing wetlands and water bodies, already has the natural infrastructure for water recharge – as do many other cities.

One only needs to recognisethe role of wetlands and numerous water bodies within the cities, and manage them sustainably.



IMPACT ON VEGETATION

The researchers also looked at the effect of temperature-induced reduction in water recharge on vegetation growth. They selected 20 river basins where natural vegetation covered 50% or more of the area, with little snow coverage.

During dry years, there was significant reduction in vegetation growth in 18 river basins.

Vegetation growth reduction (%) per centimetre reduction in terrestrial water recharge.

The Ganga-Brahmaputra and Indus basins were excluded from this analysis as they are intensively farmed or settled, but other Asian river basins like the Irrawaddy, Mekong and Amu Darya show declines in vegetation growth due to reduced water availability, raising concerns for biodiversity and agriculture.

The researchers warned of the “loss of essential ecosystem services provided by natural vegetation” due to reduced recharge.

With some scientists projecting temperatures to rise by as much as 5C above preindustrial levels by 2100, challenges lie ahead for water availability.

The burgeoning cities in these basins need to conserve and harvest rainwater through ecological planning, investing in wastewater treatment, and countering the urban heat island effect through nature-based solutions.

Call Us
Directions
Whatsapp
Enquiry