Please cite this article in press as: Webber, H., et al., Canopy temperature for simulation of heat stress in irrigated wheat in a semi-arid environment: A multi-model comparison. Field Crops Res. (2015), http://dx.doi.org/10.1016/j.fcr.2015.10.009 ARTICLE IN PRESS G Model FIELD-6563; No. of Pages 15 Field Crops Research xxx (2015) xxx–xxx Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr Canopy temperature for simulation of heat stress in irrigated wheat in a semi-arid environment: A multi-model comparison Heidi Webber a,∗ , Pierre Martre b , Senthold Asseng c , Bruce Kimball d , Jeffrey White d , Michael Ottman e , Gerard W. Wall d , Giacomo De Sanctis f , Jordi Doltra g , Robert Grant h , Belay Kassie c , Andrea Maiorano b , Jørgen E. Olesen i , Dominique Ripoche j , Ehsan Eyshi Rezaei a , Mikhail A. Semenov k , Pierre Stratonovitch k , Frank Ewert a a University of Bonn, Institute of Crop Science and Resource Conservation (INRES), Crop Science Group, Katzenburgweg 5, 53115 Bonn, Germany b INRA, UMR0759 Laboratoire d’Ecophysiologie des Plantes sous Stress Environnementaux, F-34060 Montpellier, France c Agricultural & Biological Engineering Department, University of Florida, Gainesville, FL 32611, USA d U.S Arid-Land Agricultural Research Center, USDA, Agricultural Research Service, 21881 North Cardon Lane, Maricopa,AZ 85138, USA e School of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA f European Commission, Joint Research Centre, Via Enrico Fermi, 2749 Ispra 21027, Italy g Cantabrian Agricultural Research and Training Centre, CIFA, c/Héroes 2 de Mayo 27, 39600 Muriedas, Cantabria, Spain h University of Alberta, Edmonton, Alberta T6G 2E3, Canada i Department of Agroecology, Aarhus University, Blichers Allé 20, PO Box 50, 8830 Tjele, Denmark j INRA, US1116 AgroClim, F-84914 Avignon, France k Computational and Systems Biology Department, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK a r t i c l e i n f o Article history: Received 13 April 2015 Received in revised form 14 September 2015 Accepted 9 October 2015 Available online xxx Keywords: Crop model comparison Canopy temperature Heat stress Wheat a b s t r a c t Even brief periods of high temperatures occurring around flowering and during grain filling can severely reduce grain yield in cereals. Recently, ecophysiological and crop models have begun to represent such phenomena. Most models use air temperature (T air ) in their heat stress responses despite evidence that crop canopy temperature (T c ) better explains grain yield losses. T c can deviate significantly from T air based on climatic factors and the crop water status. The broad objective of this study was to evaluate whether simulation of T c improves the ability of crop models to simulate heat stress impacts on wheat under irrigated conditions. Nine process-based models, each using one of three broad approaches (empirical, EMP; energy balance assuming neutral atmospheric stability, EBN; and energy balance correcting for the atmospheric stability conditions, EBSC) to simulate T c , simulated grain yield under a range of temperature conditions. The models varied widely in their ability to reproduce the measured T c with the commonly used EBN models performing much worse than either EMP or EBSC. Use of T c to account for heat stress effects did improve simulations compared to using only T air to a relatively minor extent, but the models that additionally use T c on various other processes as well did not have better yield simulations. Models that simulated yield well under heat stress had varying skill in simulating T c . For example, the EBN models had very poor simulations of T c but performed very well in simulating grain yield. These results highlight the need to more systematically understand and model heat stress events in wheat. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The rising temperatures expected with climate change are likely to reduce wheat yields (Asseng et al., 2015), although the impact may be moderated by positive CO 2 fertilization effects. Without ∗ Corresponding author. Fax: +49 228 73 2870. E-mail addresses: webber@uni-bonn.de, heidi.webber@mail.mcgill.ca (H. Webber). consideration of adaptations in crop variety, the dominant effect of warming is to accelerate crop development. Evidence suggests that heat stress consisting of even brief periods of high temperatures above crop specific critical thresholds (Ferris et al., 1998; Porter and Gawith, 1999; Wheeler et al., 2000; Jagadish et al., 2007; Vignjevic et al., 2015) are already causing large reductions in cereal yield (Schlenker and Roberts, 2009; Hawkins et al., 2013; Lobell et al., 2013; Fontana et al., 2015). It is expected that negative impacts of high temperature on crop yields will become more frequent with increased climate variability and higher mean temperatures (Field http://dx.doi.org/10.1016/j.fcr.2015.10.009 0378-4290/© 2015 Elsevier B.V. All rights reserved.