~ By Satvik Parashar
Cropping intensity is defined as the number of seasons in which crops are planted in a single year. An increase in tubewell construction since the 1960s has largely increased cropping intensity across India, but this has caused intense extraction of water, which has resulted in the rapid depletion of aquifers across much of India. A recent study by an interdisciplinary group of researchers estimates the association between groundwater use, crop production and groundwater depletion. This would be crucial to assess the potential production losses that may occur due to overexploitation of groundwater. The focus of the study is on winter cropped areas because winter agriculture is primarily dependent on groundwater for irrigation. The analyses is at the national level with important take-aways for central India.
Figure 1 in study: Mean winter cropped area from 2000–2001 to 2015–2016 Cropped area is shown (A) across India, (B) in a highly cropped region in Punjab, and (C) in a medium-intensity cropped region in Bihar. Pixels that were never cropped are highlighted in white, pixels that were 100% cropped across all 16 years are highlighted in dark green, and pixels for which cropped area information was not found are highlighted in gray.
India’s winter crop irrigation is facilitated by three main irrigation infrastructures: i) Dug wells (dug or sunk wells that primarily draw water from shallow depths <30 m), ii) Tube wells (drilled bore holes that primarily draw water from deeper depths >30 m), and iii) Canals (man-made delivery channels of diverted surface water). The study used high-resolution data on irrigation and agricultural production to find the association of crop production with the three given irrigation infrastructures. Linear regression analyses were restricted to the villages that had only one type of irrigation source to isolate its effects on agriculture.
It was found that tube well irrigation use is associated with a higher likelihood of winter cropping and a higher proportion of winter cropped area. Also, lower variation in the cropped area and less sensitivity to monsoon rainfall variability was observed with tube well use, when compared to dug wells and canals. For Canal irrigation, it was found that cropped area varies with respect to the distance from the canal and there was greater sensitivity to rainfall in the villages using canal irrigation. This states that canal irrigation would cause inequity in cropped area distribution.
Fig. 2 in study. Association between irrigation source and cropping intensity. Exponentiated regression coefficients and confidence intervals when estimating the percent difference compared with tube well irrigation in (A) the probability of ever having a winter crop, (B) persistent cropped area (mean from 2000–2001 to 2015–2016),(C) the coefficient of variation of cropped area, and (D) sensitivity of cropped area to interannual rainfall variability (per mm/day of rainfall) when using dug or canal well irrigation. (E to H) Exponentiated regression coefficients and confidence intervals when estimating the percent difference compared with dug well irrigation for these same metrics. Significant coefficients (P < 0.05) are highlighted in black, and nonsignificant coefficients are highlighted in light gray.
The study next took into account critically depleted regions, which are regions with a steady decline in groundwater depths and are likely to be under acute water stress in 2025. These regions include Northern Maharashtra, and parts of Madhya Pradesh and Chhattisgarh in Central India. It was found that villages in critically depleted regions would lose 68% of the cropped area if farmers lost access to all groundwater in these regions. While on a national scale, loss of all groundwater might mean a 20% reduction in the winter cropped area.
The study simulated the effects of replacing wells with canals, with the most optimistic assumption that there would be no structural limitation to expand canal irrigation to all the fields currently irrigated by groundwater. It was found that if wells are replaced with canals for irrigation, winter cropped area may decrease by 24 % in critically depleted regions and by around 7% if considered at the nationwide level. The results vary greatly across the country with northwest and Central India likely to incur the greatest amount of loss, while some regions in South India even show gains in winter crop production by switching to canal irrigation. Overall, this doesn’t make up for losses because South India contributes to only a fraction of winter crop production in India, while the entirety of India’s wheat is planted in Central and North India during the winter growing season. The study results indicate that canal irrigation might partially relieve the water stress caused due to the loss of critically depleted regions, but they cannot match the production levels achieved using well irrigation.
Fig. 4 in study. State-by-state winter cropped area loss estimates due to groundwater depletion with and without replacement with canals. Maps showing state-specific estimates of winter cropped area loss (in red) and gain (in blue) (A) if all critically depleted groundwater is lost with no replacement, (B) if groundwater irrigation is replaced with canals (using national-level regression coefficients), and (C) if groundwater irrigation is replaced with canals (using state-level regression coefficients).
India is one of the largest agricultural producers worldwide, with over 600 million farmers dependent on Indian agriculture as a primary source of livelihood. Groundwater depletion would severely affect agriculture in regions projected to have low groundwater availability by 2025. The study highlights the importance of groundwater for Indian agriculture and suggests that policy interventions and additional adaptations are needed along with canal irrigation to mitigate potential agricultural impacts. Policies that promote less water-intensive crops, water-saving technologies and efficient canal irrigation could help prevent agriculture losses. Identifying such interventions would help India maintain production losses in the face of groundwater depletion.
Original Paper: Jain, M., Fishman, R., Mondal, P., Galford, G.L., Bhattarai, N., Naeem, S., Lall, U., Balwinder-Singh and DeFries, R.S., 2021. Groundwater depletion will reduce cropping intensity in India. Science advances, 7(9), p.eabd2849.
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