Assessing crop yield in response to heat and drought stress is important in implementing the best adaptation strategies to mitigate the effects of climate change. For this aim, observations from 105 agricultural/meteorological experiments in the semi-arid (Maragheh, Qamlou and Sararoud), Mediterranean (Hashem Abad and Oltan) and semi-humid (Gharakhil) regions of Iran were used to investigate the response of the reproductive growing duration (RGD) and grain yield of rainfed winter wheat to certain climatic and agro-climatic indices consisted of precipitation (mm), growing degree days (GDDs), and cumulative extreme temperatures above wheat tolerance threshold level of ≥ 34 °C (TAT). Accordingly, multiple linear regression was applied under baseline (1998–2012) and future increasing temperature (by 1 °C and 2 °C). Results indicated that the average of wheat RGD and yield were 37.2 ± 0.71 d and 2.3 ± 0.05 t ha⁻¹ in semi-arid, 25.7 ± 0.8 d and 2.9 ± 0.11 t ha⁻¹ in semi-humid, and 21.7 ± 0.59 d and 5.25 ± 0.17 t ha⁻¹ in Mediterranean regions, respectively. The main findings showed that, on average during 1998–2012, wheat RGD and yield changed by − 0.26 d yr⁻¹ and − 0.93% (0.02 t ha⁻¹ yr⁻¹) in semi-arid, + 0.25 d yr⁻¹ and − 1.27% (0.04 t ha⁻¹ yr⁻¹) in semi-humid, and − 0.01 d yr⁻¹ and − 0.27% (0.01 t ha⁻¹ yr⁻¹) in Mediterranean regions, respectively. Precipitation and TAT had substantial positive and negative impacts on RGD by + 0.1 d yr⁻¹ and − 0.03 d yr⁻¹, and crop yield by + 0.04% and − 1.14% in all study locations. An increase in GDDs, however, significantly shortened RGD (− 0.06 d yr⁻¹) and consequently reduced grain yield (− 0.04%) in semi-arid regions, while in semi-humid and Mediterranean regions, increasing GDDs had a positive impact on RGD (+ 0.07 d yr⁻¹) and yield (+ 0.19%). Among the indices, TAT showed significantly greater detrimental effects on RGD and grain yield particularly when accompanied by less precipitation (i.e. drought stress). Our results highlighted that any increase in temperatures even by 1 °C or 2 °C would lead to drastic increases in TAT and GDDs in all study regions, most especially in semi-arid regions. Under these conditions, any benefits from precipitation would be neutralized by the negative impacts of increased GDDs and TAT in all study locations. The insights into crop response to weather variations and climate extremes provide excellent evidence and a basis for reducing crop yield damage by designing for improved heat tolerance for the future.

评估作物产量以应对高温和干旱胁迫对于实施最佳适应战略以减轻气候变化的影响非常重要。为此，伊朗半干旱地区（Maragheh、Qamlou 和 Sararoud）、地中海地区（Hashem Abad 和 Oltan）和半湿润地区（Gharakhil）的 105 次农业/气象实验的观测结果被用来研究生殖系统的反应。雨养冬小麦的生长持续时间 (RGD) 和谷物产量对某些气候和农业气候指数的影响包括降水 (mm)、生长度日 (GDD) 和高于小麦耐受阈值水平 ≥ 34 °C (TAT) 的累积极端温度）。因此，多元线性回归应用于基线（1998-2012）和未来升高的温度（1°C 和 2°C）。^-1在半干旱地区，25.7 ± 0.8 d 和 2.9 ± 0.11 t ha ^-1在半湿润地区，以及 21.7 ± 0.59 d 和 5.25 ± 0.17 t ha ^-1在地中海地区。主要发现表明，在 1998-2012 年期间，小麦 RGD 和产量平均变化为 - 0.26 d yr ^-1和 - 0.93% (0.02 t ha ^-1  yr ^-1 )，在半干旱地区，+ 0.25 d yr ^-1和 - 1.27% (0.04 t ha ^-1  yr ^-1 ) 在半湿润地区，- 0.01 d yr ^-1和 - 0.27% (0.01 t ha ^-1  yr ^-1 ) 在地中海地区。降水和 TAT 对 RGD 产生了显着的正面和负面影响 + 0.1 d yr⁻¹和 − 0.03 d yr ⁻¹，所有研究地点的作物产量增加 + 0.04% 和 − 1.14%。然而，在半干旱地区，GDD 的增加显着缩短了 RGD（- 0.06 d yr ^-1）并因此降低了谷物产量（- 0.04%），而在半湿润和地中海地区，增加 GDD 对RGD (+ 0.07 d yr ^-1) 和产率 (+ 0.19%)。在这些指数中，TAT 对 RGD 和谷物产量的不利影响显着更大，特别是当伴随着较少的降水（即干旱胁迫）时。我们的结果强调，即使温度升高 1°C 或 2°C，也会导致所有研究区域的 TAT 和 GDD 急剧增加，尤其是在半干旱地区。在这些条件下，所有研究地点的 GDD 和 TAT 增加的负面影响都将抵消降水带来的任何好处。对作物对天气变化和极端气候的反应的见解为通过设计提高未来的耐热性来减少作物产量损失提供了极好的证据和基础。