evaluation of saffron yield changes in response to temperature and rainfall variations in birjand

climate change is one of the most important factors in changing the distribution area and reducing saffron yield over the past two decades. in this study the effect of rainfall and temperature was studied on saffron yield changes in birjand, during 2004-2016. the recorded temperatures were compared with the temperature thresholds for cold stress during winter (~- 15^oc), optimal temperature for flower initiation in mid-summer (~25°c) and the optimum temperature for flower appearance in mid-autumn (~15°c). results showed that the main cold stress during the experimental period occurred in winter 2008, where the mean air temperature and the lowest recorded temperature in january were -2 and -19.6°c, respectively. the outcome of this occurrence was a considerable decline in stigma yield in the next two years (2009-2010), which was 2 times lower than 9 other years (3.83 vs 1.9 kg ha-1). the mean air temperatures for flower initiation during august, in the experimental period were between 24.5-29.9°c, while the maximum temperatures were between 34.8-41.8°c,  which aren’t suitable for the process of flower formation. similarly, the temperature in november for flower appearance was not appropriate, so that, mean, minimum and maximum air temperatures in this month during study period were between 8.8-12.3°c, -2.4 to -11.5°c and 23.1-28.2°c, respectively. the rainfall trend also revealed a decline in december and january, in the last years compared to the early years of the past decade. overall, it seems that change in climatic parameters is a main reason for high gap yield in saffron cultivation.