🌦️ Impacts of Climate Change on Indian Agriculture

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Impacts of Climate Change on Indian Agriculture

Overview

Indian agriculture, which supports the livelihoods of over 58% of the population and contributes ~17% to GDP, is acutely vulnerable to climate change. The impacts manifest across crops, livestock, water resources, pest dynamics, and coastal agriculture.

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Direct Impacts on Crop Production

Yield Decline Projections

Modelling studies using crop simulation models (DSSAT, ORYZA, InfoCrop) project significant yield declines:

• Wheat: -6% per °C rise in temperature; particularly vulnerable due to terminal heat stress during grain filling
• Rice: -3 to -7.5% per °C rise; impact varies with season (kharif vs rabi)
• Maize: -7 to -10% per °C rise; highly sensitive to heat stress at silking
• Sorghum and Pearl Millet: Relatively tolerant (C4 crops) but affected by extreme heat

C3 vs C4 Crops and CO₂ Fertilization

CO₂ fertilization — the enhancement of photosynthesis at elevated CO₂ — benefits C3 crops (wheat, rice, pulses, vegetables) more than C4 crops (maize, sorghum, sugarcane):

• C3 crops may gain 10–15% yield under doubled CO₂ in the absence of other stresses
• However, heat stress, water deficit, and nutrient limitations largely negate this benefit in field conditions
• FACE (Free-Air CO₂ Enrichment) experiments in India show much smaller gains than predicted by models

Heat Stress at Critical Growth Stages

Flowering and grain filling are the most sensitive stages:

• Temperatures above 35°C during wheat anthesis causes pollen sterility
• Rice spikelet sterility increases above 33–35°C
• Night temperature rises are particularly damaging — respiration increases without photosynthesis, reducing net assimilation
• Grain quality deteriorates — lower protein content, smaller grain size

Drought Stress

• Water deficit affects photosynthesis, stomatal conductance, and turgor-driven processes
• Extended dry spells during kharif (June–October) increasingly common in Central and Peninsular India
• Reproductive stage drought causes the most severe yield loss (50–70% reduction possible)

Flood and Submergence Stress

• Submergence causes soil anoxia, impairs root respiration, and leads to crop death within 3–7 days in intolerant varieties
• Flash floods damage standing crops at all growth stages
• Waterlogging reduces soil aeration, leading to denitrification losses and nutrient deficiency

Salinity from Sea Level Rise

• Sea level rise is causing saltwater intrusion into coastal aquifers in states like West Bengal, Odisha, Tamil Nadu, and Kerala
• Estimated 10 million ha of coastal agricultural land under threat by 2050
• Soil salinity reduces germination, nutrient uptake, and enzymatic activity

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Phenological Changes

Phenology refers to the timing of periodic biological events influenced by climate:

• Earlier flowering in wheat and mustard observed — up to 7–10 days advance per decade in some regions
• Vernalization requirement — winter crops need cold temperatures; warming winters may reduce vernalization fulfilment
• Mismatch between crop flowering/pollination cycles and traditional monsoon onset dates
• Changes in growing degree day accumulation altering crop duration

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Pest and Disease Dynamics

Climate change modifies the geographic range, population size, and behaviour of pests and pathogens:

Range Expansion

• Brown Plant Hopper (BPH) in rice — expanding northward as temperatures warm
• Fall Armyworm (Spodoptera frugiperda) — entered India in 2018; warming aids its spread
• Desert Locust — breeding season extended with warmer winters

Overwintering and Carryover

• Improved overwintering of pest populations at higher latitudes → higher pest pressure at season start
• More generations per season for many insects (accelerated development with warmth)

Disease Dynamics

• Fungal sporulation and spore dispersal enhanced under humid, warm conditions
• Wheat blast (Magnaporthe tritici) — spread facilitated by warming and humidity
• Rice sheath blight and blast incidence likely to increase
• Higher CO₂ promotes denser canopy → microclimate conducive to fungal diseases

Insect Development

• Most insects are poikilotherms — development rate increases with temperature up to a threshold
• Higher CO₂ reduces leaf nitrogen concentration → insects must consume more leaf tissue for same nutrition → increased damage

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Livestock Impacts

Heat Stress and Milk Production

• Heat Stress Index (THI — Temperature Humidity Index) > 72 causes production stress in dairy cattle
• Milk production decline: -10 to -30% in severe heat stress conditions
• Fat and protein content of milk also decrease under heat stress
• Crossbred and exotic breeds (HF, Jersey) more sensitive than indigenous breeds (Gir, Sahiwal)

Reproductive Failures

• Estrus detection failure under heat stress — silent heat
• Conception rates decline sharply when ambient temperature exceeds 32°C
• Early embryonic mortality increases under heat stress

Feed Crop Stress

• Water stress on fodder crops reduces livestock feed availability
• Decline in nutritional quality of roughage under elevated CO₂ (lower protein content)

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Water Resource Impacts

Glacial Retreat and River Flow

• Hindu Kush Himalayan (HKH) glaciers are retreating
• Short-term: increased glacial melt may temporarily increase river flows
• Long-term (post-2050): reduced dry season flows threatening irrigation in Punjab, Haryana, UP
• Approximately 500 million people depend on Himalayan river systems for water

Groundwater Depletion

• Increased irrigation demand due to higher evapotranspiration worsens groundwater depletion
• Punjab and Haryana water tables already declining at 0.5–1.0 m/year
• Climate stress compounds the existing over-extraction crisis

Rainfall Variability

• Increased frequency of both droughts and floods in the same year/region
• Reduced predictability of monsoon onset hampers sowing decisions

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Economic and Regional Impacts

Economic Losses

• Estimated $8–12 billion annual loss to Indian agriculture by 2050 (ICAR projections)
• Additional costs of adaptation: irrigation infrastructure, variety replacement, insurance
• Farmer income volatility increases with climate variability

Most Vulnerable Regions in India

Region	Primary Hazard	Crops at Risk
Bundelkhand (MP/UP)	Recurrent drought	Wheat, Gram, Oilseeds
Vidarbha (Maharashtra)	Drought, heat	Cotton, Soybean
Odisha coast	Cyclones, floods, salinity	Rice, Vegetables
Northeast India	Floods, shifting rainfall	Rice, Tea, Banana
Rajasthan	Drought, heat	Pearl Millet, Mustard
Sundarbans (WB)	Salinity, cyclones	Rice, Fish farming

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Crop-wise Yield Change Projections

Crop	+1°C	+2°C	+3°C	Key Mechanism
Wheat	-6%	-12%	-18%	Heat at grain filling
Rice (Kharif)	-3%	-7%	-12%	Spikelet sterility
Maize	-7%	-14%	-20%	Silking heat stress
Chickpea	-4%	-8%	-14%	Terminal drought+heat
Soybean	-2%	-5%	-9%	Flowering disruption
Groundnut	-2%	-4%	-8%	Pod development stress

Source: ICAR modelling studies and IPCC crop model ensembles

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Key Terms

• Phenological change: Shift in timing of biological events (flowering, harvest) due to warming
• C3/C4 crops: Photosynthetic pathways; C4 more efficient at high temperatures
• CO₂ fertilization: Enhanced photosynthesis at elevated CO₂; benefits C3 crops in isolation
• THI (Temperature Humidity Index): Measure of heat stress in livestock
• Spikelet sterility: Failure of rice/wheat grains to set due to heat or drought stress

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Detailed analysis of how climate change affects crop yields, livestock, water resources, pests, and livelihoods in Indian agriculture.
Section context	Revise this lesson with the rest of Climate Change Basics for stronger conceptual continuity.