Natural Resources, School of


Date of this Version



Published in Agricultural and Forest Meteorology 84:3-4 (April 1997), pp 233-247.



Copyright © 1997 Elsevier Science B.V. Used by permission.


Air temperature significantly affects crop phenology. Numerous experiments have shown that prevailing air temperature determines the length of crop growth stages. Irrigation field requirements depend on the length of the crop growth stages. In the present study, a physically based parametric model, YIELD, has been applied to estimate the impacts of fluctuating air temperature (due to inter-annual climatic variability and global warming) on evapotranspiration water requirements and the length of growth stages of the irrigated boro rice in Bangladesh. The YIELD model is crop specific and crop-growth-stage specific which is a compromise between area-specific regression models and complex crop growth simulation models. The model was tuned to Bangladesh's environment to represent appropriate agro-ecological conditions including soil type, depth of ground water, field size, wind regime, and percolation losses. YIELD has been validated for the length of the growth stages, length of growing season, final yield, and evapotranspiration. A baseline estimate for the boro rice phenology has been established by running the model for 12 meteorological stations located in the major rice growing regions. Based on the analysis of the past variations of air temperature and general circulation model (GCM) predictions, ten scenarios have been created to estimate the effects of these variations on the boro rice growth stages. These applications find that the planting date plays an important role in the boro rice phenology. This effect is most noticeable during initial growth stages. This study has found a non-linear relationship between decreasing air temperature and the length of the initial growth stage and a predominantly linear relationship with other growth stages. Model applications show that an increase in air temperature will provide longer and more stable thermal conditions for boro rice maturing stage. A 5% increase and a 4% decrease in seasonal total evapotranspiration will occur under each 1 ° cooler and warmer air temperature conditions, respectively. A rise in evapotranspiration will cause higher demands for irrigation water. Such conditions will put pressure on the current irrigation infra-structural facilities in Bangladesh and result in reduction of boro yields. Furthermore, variations in the percent of time required for the completion of different growth stages under various air temperature conditions will demand a reorganization of irrigation schedules.