ANALYSIS OF EVAPOTRNSPIRATION AND RAINFALL FOR AMAN RICE CULTIVATION IN DINAJPUR, BANGLADESH

Abstract

Long-term climatic variability influences crop evapotranspiration as well as crop production. This study was carried out to analyze the evapotranspiration and rainfall for beneficial planning of aman rice cultivation in Dinajpur, Bangladesh. This study assessed the impacts of climate change on actual evapotranspiration (ETc) of three popular aman rice varieties i.e., BR11, BR22 and BRRI dhan49. Daily climatic data like rainfall, daily maximum and minimum temperature, maximum and minimum relative humidity, wind speed and sunshine hour for a period of 20 years (1991–2010) were collected from the Bangladesh Meteorological Department, Dhaka, Bangladesh. Reference crop evapotranspiration (ETo) was determined by the FAO Penman-Monteith method. Actual crop evapotranspiration (ETc) of the three rice varieties at different growth stages were determined. MAKESENS trend model was used for determining rainfall trend and ETc trend. Weibull’s method was used for probability analysis and the expected rainfall and Actual evapotranspiration (ETc) at 75% probability level were estimated for different growth stages of those three rice varieties. It was found quite effective to predict the water availability for aman rice cultivation and to indicate the requirement of supplemental irrigation. Variation of crop efficient (Kc) and ETo were found. ETc varied at different growth stages over the total growing season. After probability analysis, it was clear that BR11 required supplemental irrigation of 27 mm from ‘25th July to 2nd September’ (development stage), 19 mm from ‘3 rd September to 7th October’ (mid stage) and 9 mm from ‘8 th October to 22th October’ (late stage) in Dinajpur district, when transplanted between 15th June to 24th July. Similarly, for BR22, as it was transplanted between 30th June to 8th August, then supplemental irrigation of 49 mm and 38 mm was needed from ‘18th September to 22 th October’ (mid stage) and from ‘23th October to 6th November’ (late stage) respectively. Finally, for BRRI dhan49, as it was transplanted between 21th June to 10th July, then supplemental irrigation of 4 mm was needed from ‘25th August to 28th September’ (mid stage). After analyzing trend through MAKESENS trend model, it was observed that most of the rainfall curves had decreasing trend and ETc curve had increasing trend. It will enable to optimize utilization of valuable water resources and help to create a better irrigation schedule for BR11, BR22 and BRRI dhan49 for their successful cultivation. This results can play an important role in sustainable irrigation water management under changing climate and helps to establish effective water schedule for aman rice cultivation.