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High-temperature indicators for capturing the impacts of heat stress on yield: lessons learned from irrigated wheat in the hot and dry environment of Sudan

Toshichika Iizumi*, Mitsuru Tsubo, Atsushi Maruyama, Izzat S. A. Tahir, Yasunori Kurosaki, Hisashi Tsujimoto

*Corresponding author:

ABSTRACT: High temperatures occurring during flowering and early grain filling substantially decrease cereal yields. Drawing on the accumulated evidence showing that crop canopy temperature (Tc) rather than air temperature (Ta) better explains observed yield reductions caused by heat stress, this study evaluates the usefulness of Tc versus Ta in designing high temperature indicators for agrometeorological services, including crop monitoring and forecasting. The hot and dry environment of Sudan provides an ideal testbed. Tc is derived from the combined simulation of a crop model and a land surface model. Based on regressions linking the high-temperature indicators with irrigated wheat yield variations in three regions of Sudan over the last half-century, we found that using phenological periods rather than months for the wheat season (November to February) and using Tc rather than Ta more effectively tracks the adverse effects of high temperature on yield during the key periods. The Tc-based indicators calculated for the key phenological periods have more robust multi-region applicability than the Ta-based indicators calculated for months and season, although they do not necessarily outperform the region-specific indicators in terms of explanatory power. The detected key period is the vegetative growth period for the relatively cooler region but is the reproductive growth period for the relatively hotter regions. These findings encourage agrometeorological services at the national and global levels to incorporate Tc-based indicators, which ultimately will help players in global food systems adapt to climate change by preparing for wheat supply disruptions due to high-temperature extremes.