A 51-year analysis of 563 Indian districts showed that just 1°C of warming slashes national average crop yields by about 8%.
This erases years of productivity gains.
Heat and rainfall shocks hit key staples like rice, wheat, maize and pearl millet especially hard.
Some districts suffered yield losses of up to 39%.
A single degree Celsius (°C) of warming reduces the national average yield across all crops by around 8 per cent, a new analysis found. This highlights how rising temperatures and erratic rainfall are erasing years’ worth of agricultural progress in the world’s second largest agricultural producer.
The study, titled Climate Change and Crop Yields in India, based on data from 1966 to 2016, found that both heat and rainfall shocks have large and persistent effects on agricultural productivity, with some crops suffering far steeper losses than the national average. Yields of pearl millet declined by as much as 19 per cent under a 1°C rise in temperature, while maize yields fell by more than 16 per cent, the data showed. And in the worst-affected individual districts, yields can fell by as much as 39 per cent.
The analysis by researchers at Centre for Study of Science, Technology, and Policy and the Centre for Social and Economic Progress in India and Monash University, Australia is one of the largest of its kind for India. It tracked yields across 10 major crops in 563 districts (out of 663 in 2017) over five decades, drawing on roughly 12.6 million daily weather observations.
The 10 crops studied were rice, wheat, sorghum, maize, pearl millet, chickpea, pigeonpea, groundnut, sugarcane and cotton. These account for two-thirds of India’s total gross cropped area and about two-fifths of total value-added by India’s crop sector.
The paper centres its analysis on two specific climate scenarios: A 20 per cent reduction in rainfall and a 1°C rise in temperature. Both have effects of near-identical magnitude: A 20 per cent rainfall deficit reduces national average yields across all crops by 8.2 per cent, while a 1°C temperature increase produces a 7.8 per cent reduction.
Neither shock spares any major crop category. For the rainfall scenario, five of the 10 crops suffer losses steeper than the national average: Sorghum (14.1 per cent), cotton (11.4 per cent), rice (11.2 per cent), pearl millet (10.6 per cent) and groundnut (9 per cent). For the temperature scenario, sugarcane (9.4 per cent), maize (16.2 per cent), pigeonpea (9.3 per cent), pearl millet (19.1 per cent) and sorghum (9.4 per cent) bear the heaviest burden.
The evidence indicates that the significant effects of both positive or negative temperature anomalies are always yield-reducing.
“In no case do we find evidence of a significant positive effect of hotter or cooler than normal temperatures on crop yields,” the authors said.
One of the study’s most important findings was that the immediate impact of a climate shock tells only part of the story. For all 10 crops, the long-run yield losses are significantly larger than what is observed in the year the shock occurs — and for many crops, the gap is substantial. For rice, wheat, chickpea, pigeonpea, sugarcane and cotton, the long-run impact is between 35 and 66 per cent higher than the short-run figure.
The damage also accumulates quickly. For all crops, more than 80 per cent of the total long-run loss is realised within two years of a shock and more than 90 per cent within three years. By year five, nearly the entire long-run impact has set in, leaving little time for recovery before the next weather event arrives.
Even in the short run, data revealed widespread and significant damage across nearly every crop and climate scenario studied. A one standard deviation shortfall in rainfall produced significant adverse yield impacts for nine of the 10 crops studied, with sugarcane the only exception. The short-run losses ranged from 4 per cent for wheat to 14 per cent for both sorghum and pearl millet. Rice, India’s most widely consumed staple, suffered a 9 per cent short-run decline, while groundnut, a major cash crop, fell by 10 per cent.
Temperature tells a similarly story. Hotter than normal conditions produced significant short-run yield losses for eight of the 10 crops — rice, wheat, sorghum, maize, pearl millet, chickpea, pigeonpea and sugarcane — with impacts ranging from 2 per cent for wheat to 10 per cent for pearl millet. But cooler than normal conditions offered no relief either. Significant adverse effects from below-average temperatures are recorded for five crops — rice, wheat, maize, pearl millet and sugarcane.
Further, using historical yield growth rates over the last 25 years as a yardstick, the researchers calculated that a 1°C rise in temperature was equivalent to wiping out around four years of accumulated productivity gains for both rice and wheat. For maize and pearl millet, the loss amounted to six years of growth and for sugarcane, eight. The magnitude of these impacts essentially represent real reductions in farm incomes and upward pressure on food prices for hundreds of millions of people.
According to earlier research, crop production would need to increase by 56 per cent (from 13,100 to 20,500 trillion kilocalories per year over 2010-2050) to meet the growing demand for food fuelled by population growth and richer diets. And the challenge of raising production is predominantly a challenge of raising crop yields as the country has essentially run out of new land to farm.
India’s national average annual yield growth varies from 0.4 per cent for pigeonpea and 0.9 per cent for chickpea and sugarcane to 2.9 per cent for cotton; the average yield growth for rice and wheat are 2.1 per cent and 2.3 per cent, respectively.
The study explained that over a 50-year period, these growth rates translated into large increments in yields for many crops; for instance, they imply an approximate tripling of yields for rice and wheat.
“Our findings also have implications for higher food prices contributing to inflationary pressures in the economy. Persistent high inflation erodes purchasing power, disproportionately impacts low-income households, destabilises inflation expectations and complicates monetary policy,” the researchers wrote in the report.