The impact of climate parameters on yield and yield risk of rainfed wheat and barley in West Azarbaijan province

The IPCC states that the climate is changing. Since rainfed agricultural crop yield is influenced by climatic factors, climate variables and a changing climate can affect yield and yield risk. The aim of this study is to identify the impact of climate variables and change on crop yield and the yield risk of wheat and barley in West Azerbaijan Province.
To this end, the stochastic yield function of Just and Pope was used with panel data for the period of 1383-94 for five counties in West Azarbaijan. These counties are the largest producers of these two crops in the province. To estimate the econometric models of crop yield and yield risk functions, linear, quadratic, Cobb-Douglas, transcendental and translog functional forms were used.
Results show that precipitation and average temperature have a positive effect and wind speed has a negative impact on crop yield. Maximum and minimum temperature also have different effects. Minimum temperature has a negative effect on barley yield but a positive effect on wheat yield. Whereas the effect of maximum temperature is negative for wheat but positive for barley. Additionally, average temperature has a negative effect on the yield risk of both crops and is risk-decreasing. Precipitation and average maximum temperature have a negative effect and average minimum temperature has a positive effect on the yield risk of barley. Variables that have positive effects on the yield risk of wheat are average maximum temperature and wind speed and they are risk-increasing. Average humidity during the growth season has a negative effect on the yield risk of wheat. Elasticities of the variables with regard to crop yield and yield risk of the crops has been calculated. Results of the calculation of the elasticities of precipitation, average temperature, minimum temperature, maximum temperature and wind speed with regard to yield of wheat equal 0.23, 1.75, 0.16, -1.56, and -0.16, and with regard to barley 0.52, 0.82, -0.47, 1.04 and -2.15, respectively. Average temperature has the highest positive effect on wheat yield and wind speed has the lowest negative effect on barley yield. Also, results of the calculation of elasticities of average temperature, maximum temperature, humidity and wind speed with regard to yield risk of wheat are -53.27, 66.63, -10.30 and 6.32. With regard to barley, elasticities of precipitation, maximum temperature, average temperature and minimum temperature are -2.24, -4.89, -20.48 and 34.92. Increasing maximum and minimum temperature have the highest positive impact on yield risk of barley and average temperature has the lowest negative impact.
As the results show, climate variables have an impact on crop yield and yield risk of rainfed wheat and barley in West Azarbaijan. Average temperature and precipitation have a positive impact and wind speed has a negative impact on the yield of rainfed wheat and barley. Average temperature also has a negative impact on the yield risk of both crops. The effect of precipitation on the yield risk of wheat is non-significant but has a negative impact on the yield risk of barley. Wind speed has a positive impact on the yield risk of wheat but its effect is non-significant on the yield risk of barley. In addition, results show that the impact of climate factors on crop yield and the yield risk of rainfed wheat and barley in West Azarbaijan are nonlinear and these factors do not affect crop yield and yield risk independently. The interaction of these factors, however, will affect crop yield and yield risk.