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

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

3. 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

4. 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

5. Methods

6. 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

7. 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

8. Increase in T (mean and diurnal) Increase in sat. vapour pressure Increase in VDP Decreased crop yield from reduced transpiration efficiency Fixed-duration results

9. Increase in T > Topt (28° C in GLAM) Slower crop development Longer crop duration Increased crop yield (more so for irrigated crops) Variable-duration results

10. 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

11. 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

12. Questions