© crown copyright met office case study: use of glam to investigate future crop yields over india

© Crown copyright Met Office

Case Study: Use of GLAM to investigate future crop yields over India


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


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


Methods


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


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


Fixed-duration resultsIncrease in T

(mean and diurnal)

Increase in sat. vapour pressure

Increase in VDP

Decreased crop yield from reduced transpiration

efficiency


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)


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


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 super-optimal temperatures, and more processes-based studies on the impact of VPD


Questions

© crown copyright met office case study: use of glam to investigate future crop yields over india

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