Approximation of climate change effects on crop production could be biased depending upon the uncertainties in climate change scenarios, study location and methods of crop yield prediction. We evaluated the impact of climate change on wheat yield reduction percentage by determination of adjusted evapotranspiration. Climate projections of general circulation models (HadCM3) under three scenarios (SRA1B, SRES-A2 and SRES-B1) were employed in this study for different time periods (baseline (1961–1990), 2010–2039, 2040–2069, and 2070–2099) for Mashhad location. Statistical downscaling method was employed for developing quantitative relationship between large scale atmospheric variables (predictors) and local variables (observes). From the viewpoint of climatology, such parameters were also generated by a LARS-WG5 stochastic weather generator. The results showed that climate model had acceptable accuracy in prediction of climatic variables, especially maximum temperature. B1 scenario showed the highest rainfall amount, adjusted evapotranspiration and the lowest values of maximum temperature in contrast to other scenarios. In addition, A2 scenario showed the highest values of maximum and minimum temperatures and the lowest values of adjusted evapotranspiration in all study periods. Maximum wheat yield reduction was obtained under A2 scenario (57%) for the third time period (2070–2099) in comparison with the baseline. Nevertheless, B1 scenario showed minimum change in wheat yield for all time periods. In conclusion, wheat yield reduction process in Mashhad location is extremely related to climate scenario.

Keywords