Risk assessment of heat stress to grain maize in Khuzestan province under climate change

Heat stress caused by climate change will become a restriction for maize production in the future (Cairns et al., 2013). Damage of heat stress is very strong when is occurred in a critical stages of plant growth (particularly in the flowering phase) (Teixeira et al., 2013). Non-coincidentally of flowering stage with high temperature can be reduced the negative effects of heat stress, especially in climate change conditions (Zheng et al., 2012). In this theme, a useful change in the management practices such as early planting dates (Zheng et al., 2012; Liu et al., 2013) could be considered to avoid heat stress and reduce production risk, especially climate change situations. Khuzestan province in terms of grain maize has the highest cultivated area in Iran (Anonymous, 2013). Based on this and according to the impact of climate change on reducing maize yield in the Khuzestan province (Abbas Torki et al., 2011), this study tries to assess the risk of heat stress in grain maize at the Khuzestan province under rising temperature conditions caused by climate change.
This research was conducted in six locations of Khuzestan Province to investigate the risk assessment due to heat stress in maize in the future climate change. Accordingly, the future climate in the study areas was generated using long-term (1980-2009) climate data of the baseline (included minimum and maximum temperatures, rainfall and global radiation) and AgMIP technique under two climate scenarios (RCP4.5 and RCP8.5) for the future period of 2040 -2069. Long-term simulation experiments consisted of three sowing dates (3st February, 19st February and 5th March), six locations (Ahwaz, Behbahan, Dezful, Izeh, Ramhormoz and Shushtar), two future climate scenarios (RCP4.5 and RCP8.5) in 30 years. In total, around 1620 simulation experiments were carried out. To assess the risk of heat stress on maize, it was considered the time (phase), frequency and intensity of maize threshold temperatures in its sensitive phenological phases. To this end, flowering and grain formation phases of maize were noted as the most sensitive to high temperature stress. In this study, APSIM crop model was used for simulation of maize growth and yield. The OriginPro 9.1 and R software were used to draw figures and perform statistical analyses.
Results indicated that the average temperature during the growing season in the Khuzestan province was increased under RCP4.5 and RCP8.5 (8.5 and 34.57 percent, respectively) in comparison to the baseline (27.2 °C). The highest temperature rise was obtained in the Ramhormoz (27.2 °C) on 5th March under RCP8.5. Also, the highest temperature rise during the growing season under RCP4.5 obtained in Shushtar (27.2 °C) on 19st February. In the baseline, on average, grain yield and the number of grains/m-2 in the Khuzestan province were obtained 8.8 t ha-1 and 2305.7. These values in 2050 were 8.5 and 8.7 t ha-1 and 2227.3 and 2254.3 grains/m-2 for RCP4.5 and RCP8.5, respectively. When average across sowing dates, locations and periods, the cumulative probability function for economic yield, non-economic yield and zero yield were 45.4, 13.5 and 41.2 %, respectively for common sowing dates. Under, earlier sowing date (3 February) the cumulative probability for economic yield was higher than the other sowing dates both in future and the baseline periods (65.2 percent).
Overall, the results of this study showed that common sowing date which is used by most farmers (19st February) in Khuzestan province was not optimal for both current and future periods while the early sowing date (3st February) in most locations could be considered as an effective adaptation strategy to reduce the amount of extreme temperatures risk in future and to increase grain yield under the current conditions.