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A simulation study was carried out to describe effects of climate change on crop growth and irrigation water demand for a wheat-maize cropping sequence in a Mediterranean environment of Turkey. Climate change scenarios were projected using data of the three general circulation models—GCMs (CGCM2, ECHAM4 and MRI)—for the period of 1990 to 2100 and one regional climate model—RCM—for the period of 2070 to 2079. Potential impacts of climate change based on GCMs data were estimated for the A2 scenario in the Special Report on Emission Scenarios (SRES). The forcing data for the boundary condition of the RCM were given by the MRI model. Daily CGCM2 and RCM data were used for computations of water balance and crop development. Predictions derived from the models about changes in irrigation and crop growth in this study covered the period of 2070 to 2079 relative to the baseline period of 1994 to 2003. The effects of climate change on water demand and on wheat and maize yields were predicted using the detailed crop growth subroutine of the SWAP (Soil-Water-Atmosphere-Plant) model.Precipitation was projected to decrease by about 163, 163 and 105 mm during the period of 1990 to 2100 under the A2 scenario of the CGCM2, ECHAM4 and MRI models, respectively. The CGCM2, ECHAM4 and MRI models projected a temperature rise of 4.3, 5.3 and 3.1 °C, respectively by 2100. An increase in temperature may result in a higher evaporative demand of the atmosphere. However, actual evapotranspiration (ETa) from wheat cropland under a doubling CO2 concentration for the period of 2070 to 2079 was predicted to decrease by about 28 and 8% relative to the baseline period based on the CGCM2 and RCM data, respectively. According to these models, irrigation demand by wheat would be higher for the same period due to a decrease in precipitation. Both ETa and irrigation water for maize cropland were projected to decrease by 24 and 15% according to the CGCM2, and 28 and 22% according to the RCM, respectively. The temperature rise accelerated crop development but shortened the growing period by 24 days for wheat and 9 days for maize according to the CGCM2 data. The shortened growth duration with a higher temperature reduced the biomass accumulation of both crops regardless of CO2-fertilization effect. With the combined effect of CO2-fertilization and increased temperature, the CGCM2 and RCM projections resulted in an increase by 16 and 36% in grain yield of wheat and a decrease by about 25% and an increase by 3% in maize yield, respectively.

A fi eld experiment was conducted in 2005 at the experimental station of the Arid Land Research Center, Tottori University, Japan, for comparing latent heat fl uxes from a maize (Zea mays L.) fi eld, maize transpiration, and soil surface evaporation by two diff erent methods. Th e Bowen ratio energy balance method (Method 1) was used to measure latent heat fl uxes above the maize canopy as well as between the soil surface and the canopy at 0.5-h time intervals. Th en, latent heat fl ux from maize transpiration was calculated by the diff erence between that of the maize fi eld and soil surface. In Method 2, a weighing lysimeter and sap fl ow gauges were used to measure latent heat fl uxes from the maize fi eld and maize transpiration, respectively, at 0.5-h time intervals. Th en, latent heat fl ux from the soil surface was calculated by the diff erence between that of the maize fi eld and maize transpiration. Th e coeffi cient of determination between latent heat fl uxes by the two methods was 0.72 from the maize fi eld and 0.77 from the maize transpiration. However, results indicated a low correlation between the latent heat fl uxes from the soil surface by the two methods (r 2 = 0.36). On the average, the Bowen ratio energy balance method underestimated by 6% the latent heat fl ux measured by weighing lysimeter data and overestimated by 14% that obtained by sap fl ow data resulting in a 30% underestimation of the measured latent heat fl ux at the soil surface. At daily time intervals, results were improved with relative errors around 19 and 21% for the latent heat fl uxes from the maize fi eld and maize transpiration, respectively. Finally, this study showed that the use of Method 1 for partitioning evapotranspiration at maize fi eld level is feasible. Th e use of this technique for irrigation management to improve water use effi ciency at crop fi eld level needs to be explored.

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