Interactive Effects of Elevated CO2 and Climate Change on Wheat Production in the Mediterranean Region

Global climate change could be harmful to agriculture. In particular, water availability and irrigation development under changed climatic conditions already pose a growing problem for crop production in the Mediterranean region. Wheat is the major significant crop in terms of food security. Therefore, in relation to these issues, this review gives an overview of climate change effects on wheat production in the Mediterranean environment of Turkey. Future climate data generated by a general circulation model (e.g., CGCM2) and regional climate models (e.g., RCM/MRI, CCSR-NIES and TERCH-RAMS) have been used to quantify the wheat growth and the soil-water-balance around the Eastern Mediterranean region of Turkey. The effects of climate change on the water demand and yield of wheat were predicted using the detailed crop growth subroutine of the SWAP (Soil-Water-Atmosphere-Plant). The Soil evaporation was estimated using the E-DiGOR (Evaporation and Drainage investigations at Ground of Ordinary Rainfed-areas) model. This review revealed that the changes in climatic conditions and CO2 concentration have caused parallel changes in the wheat yield. A close correspondence between measured and simulated yield data was obtained. The grain yield increased by about 24.7% (measured) and 21.9% (modelled) under a two-fold CO2 concentration and the current climatic conditions. However, this increase in the yield was counteracted by a temperature rise of 3 °C. Wheat biomass decreases under the future climatic conditions and the enhanced CO2 concentration,regardless of the model used. Without CO2 effects, grain yield also decreases for all the models. By contrast, the combined impact of elevated CO2 and increased temperature on grain yield of wheat was positive, but varied with the climatic models. Among the models, the CCSR-NIES and TERCH-RAMS denote the highest (24.9%) and lowest (6.3%) increases in grain yield respectively. The duration of the regular crop-growing season for wheat was 24, 21, and 27 days shorter as calculated for the future, mainly caused by the projected air temperature rise of 2.2, 2.4, and 3 °C for a growing period by the 2070s for CGCM2, CCSR-NIES and TERCH-RAMS respectively. The experimental results show large increases in the water use efficiency of wheat, due to the increases in CO2 concentration and air temperature. Despite the increased evaporative demand of the atmosphere, the increases in water use efficiency can be attributed to the shorter growing days and a reduction in the transpiration due to stomata closure. Unlike reference evapotranspiration and potential soil evaporation, actual evaporation from bare soils was estimated to reduce by 16.5% in response to a decrease in rainfall and consequently soil wetness in the future, regardless of the increases in the evaporative demand. It can be concluded that to maintain wheat production in the future, the water stress must be managed by proper irrigation management techniques.This research was conducted as part of the ICCAP (Impact of Climate Change on Agricultural Production System in Arid Areas) Project, a collaboration between the Research Institute of Humanity and Nature (RIHN) of Japan and the Scientific and Technical Research Council of Turkey (TÜBİTAK). The authors would like to extend their thanks to the editors, S. Kapur, T. Watanabe, M. Aydın, E. Akça and R. Kanber