Effect of climate change-induced water-deficit stress on long-term rice yield

Meteorological instruments at the station included a solarimeter, glass thermometers for mini- mum and maximum temperatures, a psychrometer, and a thermo-hygrograph. The air tem- perature, humidity, wind speed, rainfall, and sunshine duration during the cropping seasons throughout the experimental period were used for the analyses. The average, minimum, and maximum temperatures, average relative humidity, and average wind speed (2 m above the soil surface) under the four growth stages for each year were calculated as the average of the daily values in the cool and warm cropping seasons, respectively. Rainfall and sunshine dura- tions under the four growth stages for each year were calculated as the sum of the daily values in the two cropping seasons. Statistical models The reference evapotranspiration was determined using the Penman–Monteith model [22], which was suggested by the Food and Agriculture Organization of the United Nations (FAO) and the International Commission for Irrigation and Drainage as a universal model for calcu- lating reference evapotranspiration: ET0 ¼ 0:408D Rn G ð Þ þ g 900 Tþ273 u2 es ea ð Þ D þ g 1 þ 0:34u2 ð Þ ð1Þ where ET0 is the reference evapotranspiration (mm day-1), Rn is the net radiation at the crop surface (MJ m-2 day-1), G is the soil heat flux density (MJ m-2 day-1), γ is the psychrometric constant (kPa ˚C-1), T is the average air temperature (˚C), u2 is the wind speed at a height of 2 m (m s-1), es is the saturation vapor pressure (kPa), ea is the actual vapor pressure (kPa), and Δ

is the slope vapor pressure curve (kPa ˚C-1). The detailed calculation of the parameters is described elsewhere [22, 33]. The ET0 calculation was conducted using the ET0 calculator [34] according to the calculation procedures outlined in the FAO irrigation and drainage paper 56 [22]. The crop evapotranspiration (ETC) of the rice during the growth stages was calculated under standard conditions. It was assumed that crop growth or evapotranspiration were not limited by soil water and salinity stress, crop density, pests and diseases, weed infestation, or low fertility. ETC (mm day-1) was determined by the crop coefficient approach [22], whereby the effects of the weather conditions are incorporated into ET0 (mm day-1) and the crop char- acteristics into the crop coefficient (KC): ETC ¼ ET0 � KC ð2Þ The Kc values for rice during the initial, crop development, reproductive (mid-season), and maturity (late season) stages were 1.15, 1.23, 1.14, and 1.02, respectively, as estimated by Tyagi et al. [35]. The effective rainfall was calculated using the formula described in the FAO irrigation water management paper [36]: PE ¼ 0:8P 25; if P � 75 mm month 1 0:6P 10; if P � 75 mm month 1 ( ð3Þ where PE is effective rainfall (mm month-1), and P is rainfall (mm month-1). Crop water status (CWS) of rice in the growth stage was calculated as: CWS ¼ PE ETC PERC WL ð4Þ where PE is the effective rainfall (mm month-1), ETC is the crop evapotranspiration of rice PLOS ONE Effect of climate change-induced water-deficit stress on long-term rice yield

PLOS ONE | https://doi.org/10.1371/journal.pone.0284290 April 17, 2023 4 / 14