Challenges for the simulation of crop yields in

Challenges for the simulation of crop yields in a changing climate Tim Wheeler t. r. wheeler@rdg. ac. uk Crops and Climate Group

What are effects of climate on crops? Can we forecast the productivity of crops in a changing climate?

Harvest records at Chilgrove, Sussex, 1769 -1910 Data from, Russell, 1920

Harvest records at Chilgrove, Sussex, 1769 -1910

Climate and weather are vital for crops but …

Climate change that is important for crops By 2100 … • Carbon dioxide, CO 2 (emissions of 550 to 950 ppm) • Temperature (+1. 4 to +5. 5 o. C) • Rainfall amount (huge regional range) • Variability in weather (more intense storms, increased drought risk; more frequent hot days) from IPCC TAR (2001)

How are these effects on crops investigated? Plant Environment Laboratory, University of Reading

How are these effects on crops investigated? Free Air CO 2 Enrichment, FACE Courtesy of Steve Long, University of Illinois

Effects of elevated CO 2 Maize, millet, sorghum, sugar cane will not benefit Elevated CO 2 was 475 -600 ppm from Ainsworth and Long (2005)

Effects of warmer temperature Some adaptation is possible through use of varieties from Lawlor & Mitchell (2000), Baker et al (1995), Daymond et al (1997)

Warmer season. . . … or a few hot days Rice

Warmer season. . . … or a few hot days Groundnut From Vara Prasad et al (2001)

Heat stress sow flower harvest Groundnut crop growing in Andhra Pradesh, India

Variability in rainfall within a season 1975 Total rainfall: 394 mm Yield = 1360 kg/ha 1981 Total rainfall 389 mm Yield = 901 kg/ha Groundnut crop growing in Andhra Pradesh, India

Variability in rainfall and temperature within a season +32% +22% -26% -30% Soyabean - 8 days of up to 40 o. C / 40% water supply during early seed-filling at 360 / 700 ppm CO 2 from Ferris et al, 1999

What are effects of climate on crops? Can we forecast the productivity of crops in a changing climate?

Changes in crop yield from the present day to the 2080 s Potential change in cereal yields (%) 10 – 5 5 – 2. 5 – 0 0 – -2. 5 – -5 -5 – -10 – -20 No data Unmitigated emissions Parry et al. , University of East Anglia

Linking climate information to crop models general circulation model crop model

Groundnut (peanut) production in India, 1965 - 1990

Patterns of seasonal rainfall and yield of groundnut in India District level groundnut yields (kg ha-1) Mean of 1966 - 1990 Data source: ICRISAT

Patterns of seasonal rainfall and yield of groundnut in India Sub-divisional level seasonal rainfall (JJAS, cm) Mean of 1966 - 1990 Data source: IITM

Correlation between patterns of seasonal rainfall and yield First principal component of rainfall yield

Correlation between patterns of seasonal rainfall, yield and circulation First principal component of rainfall yield and PC 3 of 850 h. Pa circulation

Correlation between seasonal rainfall and yield of maize Rio Grande do Sul, Brasil 1990 -2005 Homero Bergamaschi, et al. 2006 Sites/weather stations in the main maize producer region Surrounding counties, to each weather station (micro-regions)

General Large Area Model for Annual Crops (GLAM) Combines: • the benefits of more empirical approaches (low input data requirements, validity over large spatial scales) with • the benefits of the process-based approach (e. g. the potential to capture intra-seasonal variability, and so cope with changing climates) Challinor et. al. (2004)

General Large Area Model for Annual Crops (GLAM) d(HI)/dt Yield Biomass transpiration efficiency Root system Development stage Transpiration Leaf canopy CYG water stress Soil water radiation temperature RH rainfall

Hindcasts of groundnut yield for India from Challinor et al (2004)

Impact of extreme temperatures Hadley Centre PRECIS model, A 2 (high emission) scenario 2071 -2100 Number of years when the total number of pods setting is below 50%. Sensitive variety Tolerant variety Challinor et al. , 2005

Impacts of variability in rainfall within a season 1975 Total rainfall: 394 mm Model: 1059 kg/ha Obs: 1360 kg/ha 1981 Total rainfall 389 mm Model: 844 kg/ha Obs: 901 kg/ha Groundnut yield in Gujarat

Modelling the impacts of climate change on rice Changes in rice production across Asia under 2 x CO 2 from Matthews & Wassmann (2003)

Using probabilistic climate forecasts Model average 63 ensemble members 713 kg ha-1 Observed 775 kg ha-1 Use of DEMETER multi-model ensemble for groundnut yield in Gujarat, 1998 from Challinor et al (2005)

Fully coupled crop-climate simulation to represent crop-climate feedbacks Crops ‘growing’ in Had. AM 3 Osborne et al. , (2006)

Fully coupled crop-climate simulation All-India groundnut yield (red) with simulated mean yield (black) and spatial standard deviation (grey shading). Osborne et al. , (2006)

A coupled crop-climate model run FAO statistics Area mean s. d (spatial variability) Representation of feedbacks between crops and atmosphere at an early stage Tom Osborne, University of Reading

Summary. The effects of climate on crops Crop growth and yield will be enhanced by elevated CO 2 … but, benefit could be less on farmer’s fields Warmer seasons will be shorter and yields less … but, adaptation can counter this to some extent A few days of hot temperature can severely reduce yields Crops will be vulnerable to variability in rainfall.

Summary. Forecasting crop yields Crop models summarise observations and allow predictions ahead of time Most crop models simulate fields of crops, … but, crop forecasts often needed over countries and regions, nearer to the scale of climate model predictions New developments in crop and climate modelling should improve our forecasts of crops in a changing climate

Summary. Challenges for the simulation of crop yields in a changing climate Crop observations – Magnitude of CO 2 effect, effects of climate extremes and poor soil fertility Climate models not ideal for crop prediction – Differences in spatial and temporal scale – Precipitation is key and is a difficult variable to predict Combining crop and climate models – Cascade of uncertainties

Many thanks to … Andrew Challinor Tom Osborne Julia Slingo Laurence Hansen Peter Craufurd Richard Betts David Grimes t. r. wheeler@rdg. ac. uk