Studying the changes in rice yield and water balance in Guilan province affected by climate change

Increasing greenhouse gases will have different effects on crop yields, so that the interaction of these effects may increase or decrease yields. Crop simulation models have been used to investigate different levels of crop and environmental managements. The aim of this study was to investigate the AquaCrop model based on past, present and future climate in Rasht city located in Guilan province to achieve maximum water productivity and rice grain yield.

In order to study the changes in rice yield, water balance and productivity in Rasht city located in Gilan province under the past, present and future climate, the AquaCrop model was used. For this purpose, long-term data (over 30 years) were used to evaluate the yield and water balance in rice cultivation in the past and present climate. Also, using LARS-WG6 software, meteorological data for the next 83 years were generated based on the available daily meteorological data. The AquaCrop model was evaluated in the past, present and future climates based on daily data of minimum and maximum temperatures, precipitation and sun hours. The studied treatments included four levels of irrigation including 55, 70, 85 and 100% of water requirement and the planting dates were April 21st, May 11st and May 31st. By examining the effect of different treatment levels based on RCP 4.5 and RCP 8.5 climate change scenarios, the rate of changes in grain yield, evapotranspiration and water productivity based on evapotranspiration in the past, present and future climates were investigated. Also, the best irrigation treatment and planting date were introduced to increase rice yield and reduce water consumption.

The evaluation results showed that the LARS-WG6 model is able to simulate the climatic components including temperature, precipitation and radiation with high accuracy. The results showed that the minimum and maximum temperatures increased during the climate change scenarios and the amount of radiation and precipitation decreased. The result of rice biomass and grain yield under RCP 4.5 and RCP 8.5 showed that the highest grain and biomass yield was obtained in irrigation of 100% of water requirement and planting date on April 21st. The study of water productivity showed that irrigation treatment of 100% of water requirement and planting date of May 31st had an effective role in increasing soil water storage and reducing evapotranspiration from the soil surface. The highest water productivity in grain production based on evapotranspiration was obtained in irrigation of 100% of water requirement and planting date was May 31st.

According to the obtained results, considering the water consumption productivity and yield and problems that will exist in the future including water shortage, it seems that late cultivation of rice in conditions of water shortage is a good solution, but under conditions where there is no water shortage, early cultivation of rice, such as April 21, can increase production. The study of irrigation levels showed that grain production is the most effective factor in increasing water use productivity and the use of low irrigation levels will not play an effective role in increasing water productivity.