Impacts of climate change and CO2 concentration on wheat yield in Iran and adaptation strategies

The Impact of climate change on irrigated wheat yield in Iran was studied using a simulation model under different climatic scenarios. SUCROS-wheat model which was adapted for the effect of CO2 concentration on photosynthetic parameters, were calibrated and validated against observed wheat yield obtained from different regions of country. Interaction effect of CO2 concentration and temperature on wheat yield was simulated at 3 CO2 concentrations including 350 (current), 550 and 700ppm (doubled) in combination with increasing mean daily temperature by 0 (unchanged), 1, 2, 3 and 4°C. In addition climatic conditions of the year 2050 were predicted by using GISS and GFDL General Circulation Models (GCM) based on IPCC scenarios for the target year. The GCMs were first calibrated by the long term (40 years) weather data from 25 stations located in different wheat production regions across the country. Predicted weather data of GCMs were used as the inputs of simulation model after statistical downscaling and generating daily weather parameters. Wheat yield at different regions was estimated for the climatic conditions of the target year with and without increased CO2 concentration. Finally adaptation strategies for improving wheat yield under future climate were evaluated by means of simulation model. The results showed that despite of some deviation between the two GCMs, average temperature will be changed in the range of 3.5-4.4°C with an increasing gradient from West to East and North to South of the country. This warming pattern will be led to the higher frequency of temperatures above 30°C during the flowering stage of wheat in the most regions. Increasing CO2 concentration without warming showed positive effects on wheat yield. However, the effect of CO2 was compensated for by temperature. Based on simulation results wheat yield was reduced when mean temperature was raised above 3°C even at doubling CO2 concentration. Predicted wheat yield for the year 2050 indicated that while the effects of higher temperatures was partly moderated by increased CO2 concentration the overall wheat yield will be decreased by 13-28% in different production regions. Changing planting dates and improvement of new cultivars with higher heat tolerance at flowering were evaluated as the most effective adaptation strategies for the future climate. Simulation results showed that wheat yield reduction at the target year could be prevented considerably with increasing temperature threshold of wheat cultivars at flowering by 2-4 °C