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Case Study: Use of GLAM to
investigate future crop yields over India
© Crown copyright Met Office
© Crown copyright Met Office
Introduction
• Climate change will have both direct and indirect
influences on crop growth and development
• i.e. direct CO2 effect + indirect effect of weather and climate
change
• Regional focus on groundnut (i.e. peanut) crops over
Indian subcontinent
• Aims of study:
• Identify indirect processes that are important in determining
crop yield under climate change
• Identify key uncertainties in crop yield projections
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Methods
• Domain choice over Indian subcontinent (4 regions)
• Use of GLAM over India has shown promising results for the
current climate
• Data for the future climate state is taken directly from
PRECIS regional climate simulations performed by
IITM
• Follows SRES A2 emissions path for 2071-2100
• Specific input data: solar rad., rainfall, Tmax and Tmin
• Future climate data from PRECIS suggests enhanced
monsoon, higher surface temperatures, and increased
atmospheric water content
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Methods
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Methods
• GLAM contains parameterisations of how crops
respond to weather and climate
• 36 GLAM simulations for 2071-2100
• 18 with variable-duration crop
• 18 with fix-duration crop with respect to baseline info
• Fixed-duration experiments assess indirect impact of
elevated CO2 on crop yield (primarily due to increased
VPD - next slide)
• Excludes impact of mean T on duration
• Variable-duration experiments assess impact of mean
temperature changes (specifically exceedance of
Topt) on crop yield
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Vapour pressure deficit (VPD)
• VPD = difference (deficit) between the amount of
moisture in the air and how much moisture the air can
hold when it is saturated
• For this study, VPD is estimated two ways
• Based on mean daily temperature and relative humidity
• Based on Tmax and Tmin
• ↑ in VPD related to ↑ in temperature:
• Mean temperature, which allows atmosphere to retain more
moisture
• Diurnal temperature range (Tmax minus Tmin)
• Would lead to reduced crop yields due to enhanced
water stress
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Fixed-duration results
Increase in T
(mean and diurnal)
Increase in sat.
vapour pressure
Increase
in VDP
Decreased crop yield from
reduced transpiration
efficiency
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Variable-duration results
Increase in T > Topt
(28° C in GLAM)
Slower crop
development
Longer crop
duration
Increased crop yield (more
so for irrigated crops)
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Uncertainty in results
• Variability in yield response to climate change is
comparable in magnitude to the mean simulated
change
• This is more pronounced in simulations of exceeding Topt
• Confidence is highest for regions which do not exceed Topt
(project large decreases in crop yield)
• Results can still be used to suggest implications for
future assessments of crop yield under climate
change
• When comparing results with other crop models, there
is some agreement in projection of crop yield
reduction over India
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Summary
• In general over India, crop yields are projected to
decrease with climate change
• This is due to ↑ VPD, which reduces water availability
• When T>Topt, crop yield increases for both rainfed
and irrigated crops (but more so for irrigated)
• Due to longer crop duration
• More research is needed into crop response to superoptimal temperatures, and more processes-based
studies on the impact of VPD
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Questions
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