- The total estimated groundwater depletion in India is in the range of 122–199 billion metre cube.
- With 230 billion metre cube of groundwater drawn out each year for irrigating agriculture lands in India, many parts of the country are experiencing rapid depletion of groundwater.
- The Indo-Gangetic Plain, northwestern, central and western parts of India account for most intensive groundwater-based irrigation.
- And among these regions, western India and the Indo-Gangetic Plain have more than 90% of the area irrigated using groundwater.
- While districts with significant decrease in groundwater are located in the Indo-Gangetic Plain, northwest, and central (Maharashtra) regions, a few districts in Punjab show substantial decline in groundwater table.
- With depletion occurring at a rate of 91 cm per year, Punjab has been witnessing a steep decline in groundwater table since 1996.
- In northwestern India, the amount of groundwater extracted exceeds the total recharge leading to groundwater depletion
- In contrast, some districts in western India, east coast and peninsular India have witnessed an increase in groundwater levels.
- Low-intensity rainfall during the monsoon is responsible for groundwater recharge in northwest and northcentral India.
- The study also found that carbon dioxide emission from pumping groundwater and release of carbon dioxide into the atmosphere from the soil when groundwater is depleted is less than 2-7% of the total carbon dioxide emissions in India.
- If groundwater is depleted and the region experiences drought for two–three years consecutively, there will be serious challenges. Availability of even drinking water will be a huge problem.
- Natural recharge during monsoon may not help much if groundwater depletion becomes acute, as rainfall of past several years controls the current groundwater storage levels.
Groundwater management using Tensiometers
- More than 500 tensiometers to visually monitor soil moisture conditions in rice fields and irrigate the crops only when required were used in five districts in Punjab.
- Irrigation based on information provided by the tensiometers helped farmers in the five districts save 10–36% groundwater.
- Using groundwater to irrigate the field only when necessary led to a reduction in electricity consumption and greenhouse emissions.
- The tensiometer gives visual information about the availability of soil moisture conditions.
- Irrigating the field based on this information will help conserve groundwater.
- The tensiometer is 2–3 feet long and has a ceramic cup containing numerous tiny pores at the bottom.
- It is inserted up to 8 inches into the soil, which is beyond the root zone of rice.
- The water inside the tensiometer reaches equilibrium with soil moisture, and rises or falls depending on the amount of moisture in the soil.
- Farmers are advised not to irrigate the field when the water level in the tensiometer is in the green zone.
- When the soil gets dry the water level in the tensiometer drops and reaches the yellow zone in the device.
- Farmers should start irrigating the field at this time and never allow the water in the device to reach the red zone.
- The instrument is quite accurate in monitoring soil moisture.
- One device per farm would be sufficient, especially when the terrain is nearly flat.
- So far, over 22,000 tensiometers, manufactured by Punjab Agriculture University, have been given to rice farmers in Punjab.
- Since stopping or reducing the subsidy in electricity prices may not be possible, farmers in the regions where groundwater depletion has already occurred should consider cultivating less water-intensive crops, use better irrigation technologies and irrigate crops only when necessary.
Section : Environment & Ecolog