Climate’s ‘time bomb’ for world’s groundwater has some serious lessons for Indian cities

Extreme weather events such as droughts and heavy precipitation days are two of the major impacts of global warming. These events, whose frequency and intensities are increasing by the years, may make groundwater replenishment rate too slow in dry areas, a recent study published in Nature Climate Change says.

According to this study led by Dr Mark Cuthbert from Cardiff University UK, it could take more than a century – in more than half of the world’s groundwater systems – to completely respond to environmental changes. This is being described as a climate ‘time bomb’ as the slow recharge will make it difficult for groundwater reserves to replenish in the natural timeline and may affect billions of people. It is estimated that more than two billion people across the world rely on groundwater for drinking and irrigation purposes. Groundwater is the largest usable source of freshwater on the planet but is more vulnerable to climate change than surface water, confirms this study.

According to the lead researcher, groundwater systems take a lot longer to respond to climate change than surface water, with only half of the world’s groundwater flows responding fully within ‘human’ timescales of 100 years.

Climate science has already warned that changes in rainfall intensity are very significant for groundwater. According to this study it’s not just the overall amount of rainfall that is important; it is also how intense the rainfall is. The groundwater resources are predominantly recharged by rainfall. At the same time, water exits or discharged from groundwater resources into lakes, streams and oceans to maintain an overall balance. Evidences show that in arid areas, the recharge rate will be very slow under climate change conditions. In arid areas, this research found out, groundwater reserves took much longer – in some cases thousands of years – to respond to changes in climate when compared to those in humid areas of the world.  Giving example of the Sahara, the lead researcher maintained that portions of the groundwater underneath this region are still responding to climate change from ten thousand years ago when it was much wetter there. This research, as claimed by the team, has shown one of the “hidden” impacts of climate change and has called for unprecedented actions to ensure that the future generations are not impacted by the crisis.

Extreme rainfall events and droughts go hand in hand

A just concluded study by NASA warns that warming of the tropical oceans due to climate change could lead to a substantial increase in the frequency of extreme rain storms by the end of the century. This research found out extreme storms – those producing at least 0.12 inches (3 millimetres) of rain per hour over a 16-mile (25-kilometer) area – formed when the sea surface temperature was higher than about 82 degrees Fahrenheit (28 degrees Celsius). They also found that, based on the data, 21 percent more storms form for every 1.8 degrees Fahrenheit (1 degree Celsius) rise of ocean surface temperatures. The researchers for this study claim that their data provide the first quantitative estimate of how much the severe storms are going to increase in warmer oceans, at least for the tropical oceans. 

A study by researchers at the Indian Institute of Technology, Gandhinagar claims to have established the link between anthropogenic emissions and rising trend in extreme rainfall events in India.

The study finds out that such extreme events are on the rise due to anthropogenic warming, and this trend is likely to become more prominent by the mid-century, especially in southern and central India. 

This study says extreme rainfall events are on the rise in India and attributes the trend to man-made emissions – what scientists call anthropogenic warming. Not just this, the trend is likely to become more prominent by mid-century, particularly in southern and central India. Another study finds out that there has been a three-fold increase in widespread heavy rainfall events in the 66-year period between 1950 and 2015.  Even though there has been a general weakening of monsoon circulation, there has been a 10 to 30 percent increase in rainfall events over the region where more than 150 mm rainfall is registered in a day. 

Indian cities at severe risk, need to act fast

India is already witnessing an increase in both extreme precipitation events as well as droughts. The disturbed rainfall pattern across the nation makes many areas vulnerable to low groundwater recharge. A NITI Aayog report has waned that 21 Indian cities are expected to run out of groundwater just by next year i.e. 2020.  This will affect at least 100 million people. The report also warned that critical groundwater resources that account for 40 percent of India’s water supply are being depleted at unsustainable rates.

Our cities are becoming synonymous to concrete jungles.  They are developing at the cost of natural spaces squeezing thereby the chance of rainfall penetration into the ground reserves.

The natural sponges – in the form of surface water bodies, green vegetation cover and rivers, streams etc – are vanishing fast from our cityscapes. If they are serious about the scientific studies in discussion here and many more researches that have already established in clear terms that increased dry days and growing intensity of extreme rainfall days will make groundwater recharge further slow if we prevent the rainfall from percolating down the groundwater resources. 

Our cities must act fast and move towards an integrated approach of development that makes urban forestry and water harvesting, through natural ecosystem based systems, an integral part. We need to free the top soil from as much concrete as we can and replace the same with natural green and blue infrastructure. This will not only help our cities fight the severe water crisis they are already in, but also help them move towards water security in future as climate change impacts grow.  

This article was first published in Urban Update