Effects of climate change on agroclimatic indices in rainfed wheat production areas of Iran

Despite the importance of all climatic parameters for crop growth and productivity, temperature and rainfall are more crucial compared to others and almost all climatic and agroclimatic indices are based on these two variables. Climate change will lead to variation in agroclimatic indices and evaluation of this variation is a key to study crop response to future climatic conditions. Length of growing period (LGP) and rainfall deficit index could be used as indictors for assessment of potential impact of climate change of rainfed systems. To study this impact long-term weather data of main rainfed wheat production areas of Iran were collected. UKMO general circulation model was used for perdiction of climatic parameters of selected stations for years 2025 and 2050 based on pre defined scenarios of IPCC for this target years. LGP, length of dry season and rainfall deficit index were calculated from present data and the generated data for target years. The results showed that LGP based on temperature would be increased in all rainfed areas of country. However, including the water availability in the calculation was led to a lowered LGP. Reduction of LGP for the studied stations was in the range of 8-36 and 19-55 days for years 2025 and 2050, respectively. Rainfall deficit index for 2025 and 2050 was varied, respectively at 8.3-17.7 and 21.1-32.3 mm. It was estimated that under climatic condition of years 2025 and 2050 the cultivated areas in the main rainfed production regions of the country would be reduced by 16-25 and 23-33%, respectively