Climate change impacts on irrigation water requirement, crop water productivity and rice yield in the Songkhram River Basin, Thailand

This study assesses the impacts of climate change on irrigation water requirement (IWR), rice yield, and crop water productivity (CWP) of the Thai Jasmine rice in the Songkhram River Basin of Thailand. The analysis was conducted using DSSAT crop simulation model with an ensemble of five Regional Circulation Models (RCMs) under RCP4.5 and RCP8.5 scenarios. The projection of future climatic conditions shows an increasing trend in both maximum and minimum temperatures which are expected to rise by 1.9 °C under RCP8.5 scenario by 2080s (2070-2094). Rainfall during the rainfed rice growing season may decrease in the 2030s (2020-2044), and increase in the 2055s (2045-2069) and 2080s for both scenarios. Although the total rainfall is expected to increase, rainfall during the rice reproductive phase (September to October) may decrease. The study also found that changes in rainfall have more significant influence on rice yield than temperature, possibly increasing water stress in the future. Temperature rises could increase crop water usage and higher rainfall alone may not be sufficient. IWR is expected to increase in the future. Rainfed rice yield may reduce by 14% under RCP4.5 scenario, and 10% under RCP8.5 scenario by 2080s. Due to the increment of crop water use and decrease in rice yield, CWP could reduce by 32% under RCP4.5 scenario, and 29% under RCP8.5 scenario by 2080s. The results of this study are helpful in formulating adaptation measures to address water stress and increase rice yield and CWP under climate change scenarios in the basin.