On the Changing Cool Season Affecting Rice Growth and Yield in Taiwan

Abstract

In the subtropical climate of Taiwan, the cool season (January-June) is most productive for rice cultivation. However, the cool season also sees a large variability and weather impact on the crop. To assess the effect of winter monsoon variability and the warming climate, a common ORYZA(v3) model was used to derive the potential growth and yield of the japonica rice variety in different agro-climatological areas of Taiwan. The simulation was constructed for three planting dates (15 January, 30 January, and 14 February) in three time periods (1986-2005, 2006-2025, and 2026-2045) under a high-emission (RCP8.5) scenario, using a dynamically downscaled regional climate simulation data set (CORDEX). The result indicates that increased temperature during the early season significantly shortens the rice vegetative phase in all planting dates. Compared to the 1986 condition, rice maturation is projected to be 6-9 days and 7-11 days earlier by 2045 for the central-west and the north-east regions, respectively. In the future, decreased duration of crop growth will lead to a lowered yield, while increased CO2 can enhance rice yield by 8.5-18%. Rice yield is projected to decline by 3.3-to-10% during 2026-2045, offsetting the fertilizing effect of increasing CO2. Meanwhile, yield variability will increase in the future, due to more exposure to extremely low- and high-yield conditions. As such, a large yield reduction resulting from the increased variability (down to 34%) can offset the increased mean yield.