a study of the effects of climate change on length of growing season in several climatic regions of iran

in agricultural meteorology, the growing season is the period within each year when crops can be grown from a view of thermal conditions. this period is in general, between the last and first frost dates in spring and autumn when temperature is above a specific threshold. there are two other definitions when using a 5 °c as threshold. one of the methods employed in studying future climate is using the general circulation models (gcms), but these models bear low temporal and spatial resolutions and can’t show local changes. in this study, statistical model lars-wg has been used for downscaling gcm's outputs under a2 and b1 emission scenario conditions in several climatic regions of iran during the period of 1961-2004 for an estimation of growing season length (gsl). the results revealed that growing seasons of 0°c threshold (under the two scenarios) will increase during 2020 to 2050 in mashhad, tehran and rasht stations while decrease in kerman, gorgan, and tabriz in comparison with their past climates. gsl with 5°c threshold under two scenarios will increase in all the stations except for shiraz station. in general gsl for all the three definitions under both scenarios would increase in mashhad, rasht and tehran. in case of esfahan, no significant trend was observed, using 0°c threshold and b1 scenario, and an increasing trend observed for the rest of the conditions.