Investigating the Probability of Occurrence of Evapotranspiration in Different Climates and Planting Dates of Rice in Non-Northern Regions of Iran

Changes in evapotranspiration values of rice plants in non-northern regions of the country were estimated for three different planting dates (early, on time and late planting) and with four different probabilities of 75%, 50%, 25%, and 10% (years with low, medium, high, and very high evapotranspiration, respectively), using the Penman-Monteith Equation and meteorological data of 15 stations with a statistical period of 30 years (1990-2020). The crop coefficient of rice in different stages of growth were calculated as an average in 10-day periods based on the Weibull Model. The results showed that, in all non-northern climatic regions, adopting an early planting strategy leads to a reduction in water requirement in all evapotranspiration scenarios. Adopting early planting strategy in years with very high evapotranspiration reduces the water requirement of rice in hot, cold and temperate regions by 125.9, 113.5, and 115 mm, respectively, during the growing season (on average 0.7 to 9. 0 mm per day) compared to late planting. However, in cold and temperate climates, there was no big difference between early planting and timely planting and even late planting. So, it is better to use late planting to avoid the possibility of late frosts. Comparison of the results of evapotranspiration rate of rice plant in all planting dates and different probability levels in cold, moderate, hot and very hot climate regions showed that the highest evapotranspiration rate is related to the hot region at the rate of 1021, and moderate and cold regions have much lower evapotranspiration rate than hot regions with evaporation rates of 784.8 and 729 mm, respectively. Therefore, considering the lack of water resources and the negative effects of climate change in arid or semi-arid regions such as Iran, it is better to avoid rice cultivation in hot regions, especially in years with high evapotranspiration. Also, it is better that in cold and temperate regions, the type of irrigation management and the design of structures and water systems should be adapted to the calculations of years with high evapotranspiration.