Occurrence of climate change and its effect on sowing date, length of growing cycle and evapotranspiration of winter wheat (case study: Behshahr)

In this study, impact of climate change on sowing date, length of growing season and evapotranspiration of wheat in Behshahr area is evaluated. Detection of climate change was first evaluated by means of Mann-kendall and Sen Estimator trend tests. Results indicated that no significant changes were observed in precipitation for different seasons. Temperature, however, showed an increasing tendency in summer, autumn and winter seasons. Subsequently, changes in Maximum and Minimum temperature were then simulated using HadCM3 and CGCM3 climate projection models run under the IPCC scenario A2 were downscaled at local level using statistical technique for 2011-2040, 2041-2070 and 2071-2100 periods. Wheat’s phenological stages and length of growing cycle were estimated using the Growing Degree Day Index (GDD). Potential evapotranspiration (ETo) was calculated using Hargreaves – Samani method. For future periods, results showed that, temperature would increase by one to two degrees in all months by 2100. Under such conditions in the future, the appropriate sowing period will extend by 9 to 27 days and the growing cycle length will decrease by 4 to 14 days. Crop evapotranspiration will also increase during the growing cycle, but total crop evapotranspiration will reduce due to shortening of crop cycle duration.