Short-lived climate pollutants-SLCPs have had significant impact on crop yields in India in recent decades. UP, the main wheat-producing state has been hit especially hard while rice-producing states in the heavily polluted northern Indo Gangetic Plains have also been significantly negatively affected

Tropospheric ozone and black carbon (BC), the two potent short-lived climate pollutants (SLCPs), have severely affected wheat and rice production in India over the past three decades. According to a study, averaged over India, yields in 2010 were up to 36% lower for wheat than they otherwise would have been, absent climate and pollutant emissions trends, with some densely populated states experiencing 50% relative yield losses.

The study by Jennifer Burneya and V Ramanathanb is published in PNAS journal

It says, between 1980 and 2010, emissions of black carbon and ozone precursors have risen dramatically in India that has directly affected agriculture production. The main sources of BC in India are domestic biofuels—wood, dung, and crop residues for cooking—and fossil fuels.

It says, "Yields for wheat and rice in India have recently begun to level off or even drop in some states. This trend, particularly for wheat, counters decades of increasing yields driven by technological innovation. At the same time, growing season temperature trends have been positive for major wheat and rice- producing Indian states. Studies have shown that these climate trends have had a negative impact on Indian agriculture, reducing relative yields by several percent. However, although temperature and precipitation changes have and will continue to impact future yields, these two variables alone do not tell the entire story of India’s changing crop yields."

There is substantial variation in relative impacts of climate and SLCPs across states. Some of the most dramatic impacts for both wheat and rice have occurred in Uttar Pradesh and Uttaranchal (UP). UP, India’s most populous state is the largest producer of both wheat and rice in the country, providing over one-third of India’s wheat and 14% of India’s rice. In particular, wheat yields for UP are about 50% lower than they otherwise would have been absent climate and pollution trends, and over two-thirds of that relative yield change (RYC) is attributable to SLCP emissions trends.

Rajasthan, although producing a lower percentage of India’s wheat, shows the greatest overall wheat RYC of more than 50%. The relatively large climate affects wheat in both UP and Rajasthan, which are driven by temperature, as the two states have had the largest increases in growing season temperature since 1980, 0.87° for Rajasthan and 0.52° for UP.

Four of the main wheat-producing states—UP, Rajasthan, Madhya Pradesh and Chhattisgarh, and Bihar and Jharkhand—have large negative SLCP impacts, whereas Punjab and Haryana show little to no impact of either SLCPs or climate not statistically significant at 90%.

Moreover, the uncertainties in Punjab and Haryana are greater than for other states, and across alternative models specifications. Two factors likely explain these differences. First, Punjab and Haryana are the most technologically advanced wheat-producing states in India, with the highest yields and the greatest yield gains over the period; they also feature some of the lowest estimated crop yield gaps in India and the world, meaning they have been closest to achieving biological potential despite climate and emissions changes. However, in addition, the intricacies of ozone production likely explain the SLCP impact differences.

For rice, the overall climate and pollution impacts are lower, and the state-by-state variation is less than for wheat. Most notably, the south-eastern states of Tamil Nadu and Andhra Pradesh show higher relative climate impacts; these are two of the least-polluted states in the study region; they have also featured significant growing season temperature increases.

The states of the heavily polluted northern and eastern Indo Gangetic Plains (UP, Bihar and Jharkhand, West Bengal) all exhibit SLCP RYC of about 5% or more. Haryana and Punjab, the two states with the smallest SLCP impacts in wheat, do not diverge from the other states in rice impacts. The difference in SLCP impacts between the two crops for Punjab and Haryana is likely dominated by differences in rates of ozone formation in the two states between the two seasons.

"Our results nevertheless indicate that SLCPs have had significant impact on crop yields in India in recent decades. The main wheat-producing state (UP) has been hit especially hard; rice-producing states in the heavily polluted northern Indo-Gangetic Plains have also been significantly negatively affected. For context, the yield loss for wheat attributable to SLCPs alone in 2010 (-18.9%) corresponds to over 24 million tons of wheat: around four times India’s wheat imports before the 2007–2008 food price crisis and a value of about $5 billion. Mitigation of SLCP emissions in India could thus have important food security impacts both domestically and internationally," the study concludes.