Climate change will likely increase crop water demand; farmers may adapt by applying more irrigation
The rate of depletion of groundwater in India during 2041-2080 will be thrice the current rate with global warming, according to a new report.
As the country becomes warmer, people will draw more water from underground, leading to faster depletion, the researchers wrote in the paper published in Science Advances open access multidisciplinary journal September 1.
The situation can occur despite the projected increases in precipitation and possible decreases in irrigation use as groundwater tables fall, the authors noted.
The report stated:
The projection that continued warming may triple groundwater depletion rates over the coming decades was made under a business-as-usual scenario. This is critical, given that more than 60 per cent of the nation’s irrigated agriculture depends on groundwater and portions of India are already facing severe groundwater depletion.
To date, no study accounted for the potential increase in depletion caused by warming-induced increases in irrigation in India, the authors claimed.
Across climate change scenarios, the researchers found that their estimate of groundwater level (GWL) declines from 2041 to 2080 is 3.26 times current depletion rates on average (from 1.62-4.45 times) depending on the climate model and Representative Concentration Pathway (RCP) scenario.
RCPs are a method for capturing those assumptions within a set of scenarios. The conditions of each scenario are used in the process of modelling possible future climate evolution.
Using historical data on groundwater levels, climate and crop water stress, the study researchers found that farmers have adapted to warming temperatures by intensifying groundwater withdrawals, substantially accelerating groundwater depletion rates in India.
The study findings revealed that warming temperatures have accelerated groundwater depletion as farmers have increased the amount of irrigation used to meet growing crop water demand.
While increasing irrigation use successfully minimises the negative impacts of warming temperatures on crop water stress, the resulting groundwater depletion can reduce farmers’ abilities to irrigate over decadal time scales, the report argued.
This previously unquantified cost of adapting to warming temperatures will likely further threaten India’s food and water security over the coming decades, the authors added.
“Historically, farmers have been able to maintain groundwater irrigation as water tables fall largely because of policies that facilitated groundwater extraction and a largely ungoverned groundwater irrigation economy. Increased access to borewells, free or subsidised electricity and a lack of electricity metering have allowed farmers to withdraw groundwater on demand, leading to overexploitation,” the authors of the report suggested.
To reduce this overexploitation, they recommended that effective policies are needed for rationing the power supply, metering electricity usage, regional water resource development and allocation, rewarding farmers that invest in groundwater recharge and reducing or removing energy subsidies.
In addition, groundwater-saving interventions such as the use of efficient irrigation technologies (drip or sprinkler irrigation), cultivation of less water-intensive crops and supplemental irrigation through canals may also be needed, the experts suggested.
Previous work had shown that a portfolio of such policies can enhance groundwater conservation, they observed.
While challenges remain in implementing new regulations and interventions across the hundreds of millions of households that face groundwater depletion, without such measures, the study results suggest that groundwater depletion rates will likely accelerate under climate change.
“Warming-induced groundwater pumping will also likely increase the area facing groundwater overexploitation in the future. Currently, most overexploitation of aquifers is concentrated in the northwest and south India, but the study results further suggest overexploitation may expand to include aquifers in the southwest, the southern peninsula, and central India by 2050,” the report stated.
Such an expansion, the research stresses, is of concern because south and central India have hard rock aquifers that are more difficult to recharge and have less storage capacity against the alluvial aquifers found in northwest India.
“It is therefore more likely that farmers in these systems will lose their ability to irrigate if aquifers become overexploited. Consequently, water-saving policies and interventions that are currently focused on northwest India need to consider south and central India,” the researchers noted.
Targeting water-saving policies and interventions to these regions before substantial groundwater depletion occurs could help farmers maintain their ability to irrigate and cope with warming temperatures over the coming decades, the research further recommended.
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