چكيده لاتين :
Introduction: One of the most important consequences of the future climate change is its impact on water
use and water use efficiency (WUE) in agriculture which could challenge the water resources management.
Khuzestan province is one of the most important areas of crops production in Iran particularly for wheat, so that
15.73 percent of total irrigated wheat production and 8.85 percent of total arable land is located in this province.
Therefore, investigating climate change effects on irrigated wheat production, WUE and irrigation requirement
will be necessary in the Khuzestan province. In this context, this study was conducted to simulate the growth and
yield of irrigated wheat under climate change conditions, and to calculate WUE and irrigation requirement in this
province.
Materials and Methods: The current study was done at six locations of Khuzestan province in southwestern
Iran, included Ahwaz, Behbahan, Dezful, Izeh, Omidiyeh and Ramhormoz. Historical daily weather data
including solar radiation (MJ m-2 d-1), precipitation (mm) and maximum and minimum temperatures (°C) for the
baseline period gathered for each study location from their established meteorological stations. To predict the
climatic variables in the future, HadCM3 climate model was applied under three emission scenarios (B1, A1B
and A2) for one future time period (2046-65). The observed historical daily weather data at each location was
used to generate the future scenario files to be applied in LARS-WG (Long Ashton Research Station-Weather
Generator) program. These parameters are necessary for future projection of weather variables. The downscaled
daily weather data obtained from the LARS-WG included maximum and minimum temperatures, rainfall and
solar radiation for each period of future climate. These data are required for running crop simulation model. The
Agricultural Production Systems simulator (APSIM) was used to predict the impacts of climate change on wheat
yield, WUE and irrigation requirement. The model requires daily weather variables (maximum and minimum
temperatures, precipitation and solar radiation), soil properties, type of genotype (as cultivar-specific
parameters), and crop management information as inputs to simulate crop growth and development. In order to
evaluate the climate model NRMSE (Normalized Root Mean Square Error) index was used. Finally, the outputs
obtained from the model simulation experiments were analyzed using excel, SAS and Sigma Plot.
Results and Discussion:Results of climate model evaluation indicated that LARS-GW well predicted
radiation (NRMSE from 0.63 to 1.67%), maximum (NRMSE from 0.63% to 1.05%) and minimum (NRMSE
from 0.63% to1.97%) temperatures. However, the accuracy in prediction of rainfall (NRMSE from 11.42% to
21.47%) was not as good as the other climatic variables. The simulation results in the baseline by APSIM-Wheat
showed that maximum and minimum grain yield were obtained in the Izeh (6764.2 Kg.ha-1) and Omidiyeh
(5230.2 Kg.ha-1), respectively. Under climate change conditions (rising temperature and elevated CO2), on
average, the highest and lowest grain yield were obtained in Izeh (7755.3 Kg.ha-1) and Omidiyeh (6290.76
Kg.ha-1), respectively. The simulation results in the baseline also indicated that the highest and lowest
evapotranspiration (ET) were obtained in the Izeh (441.7 mm) and Ramhormoz (401.5 mm), respectively. When
averaged acrossall future scenarios, themaximum and minimum ET were obtained in Izeh (409.56 mm) and
Ramhormoz (375.38 mm), respectively. The future rising temperature will intensify the ET, whereas reducing
stomata conductance due to higher CO2 concentration in one hand, and shortening growing period due to rising
temperature on the other hand, will reduce the cumulative ET in wheat.The simulation results in the baseline
showed that the highest and lowest WUE were obtained in Izeh (15.32 Kg.ha-1.mm-1) and Omidiyeh (12.7 Kg.ha-
1.mm-1), respectively. In climate change conditions (rising temperature and CO2 elevated), on average the highest
and lowest WUE were obtained in Izeh (18.93 Kg.ha-1.mm-1) and Omidiyeh (15.76 Kg.ha-1.mm-1), respectively.
Wheat crop would be benefitted under future climate change in Khozestan province as it is a C3 plant, and under
optimal conditions (no water and nitrogen limitations), it will produce more grain because of reduced stomata
conductance and increased photosynthesis and WUE owing to elevated CO2. Simulation results also indicated
that under climate change conditions, on average, the highest and lowest irrigation requirement were obtained in
Ahwaz (315.39 mm) and Izeh (225.96 mm), respectively.The reduced irrigation requirement of wheat under
climate change conditions could be attributed to decreasing length of growing season and increasing CO2
concentration.
Conclusion: In the current study, the effects of climate change caused by rising temperature and elevating
CO2 concentration on WUE, irrigation requirement, growth and yield of wheat were investigated in the
Khuzestan province. The simulation results showed that, wheat grain yield under climate change conditions
(averaged across all scenarios) will increase by 16 % compared to the baseline. In addition, WUE will be
increased 23 percent owing to increasing grain yield (+16%) and decreasing ET (5%) under different scenarios.
Overall, under climatic conditions of Khuzestan province in 2046-2065, WUE would be increased by 23% and
irrigation requirement would be decreased by 9%. The reasons behind these increases and decreases are rising
temperature (7%), elevating CO2 concentration (up to 526 ppm for 2046-65) and decreasing the length of
growing season and ET both by 5%.
