Abstract
Reference crop evapotranspiration (ETo) is essential for planning and management of irrigation to ensure optimum utilization of a region’s available water resources. ETo being an indicator of atmospheric evaporative demand provides a measure of the integrated effect of climatic parameters like solar radiation, wind, temperature and humidity. Variation of these climatic parameters over long period of time alters ETo. The modified ETo is crucial for periodic adjustment of irrigation planning and management. This study evaluated variation of ETo and contribution of the climatic parameters to ETo-variation in Mymensingh region of Bangladesh by analyzing climatic data of 28 years (1990–2017). ETo was determined by FAO Penman-Monteith method and trends of ETo and its governing climatic parameters were evaluated by MAKESENS trend model. The ETo-governing climatic parameters revealed contrasting trends, which also varied in different months of the year. Net radiation and wind speed showed decreasing trend, while temperature and saturation vapor pressure deficit showed increasing trend. In spite of contrasting contributions of the climatic parameters, their combined effect reduced ETo with a resulting decreasing trend of the monthly average daily ETo over the months of the year except July. These results enhance our understanding of the effects of climate change on ETo and can help correct-planning of water resources for irrigated agriculture.
 J. Bangladesh Agril. Univ. 17(2): 258–264, June 2019
Highlights
Evapotranspiration is a vital dynamic component of hydrological cycle
A declining trend in ETo was reported for Dhaka and Mymensingh regions in Bangladesh (Karim et al, 2008), north-west hydrological regions of Bangladesh (Rannu et al, 2013; Kader et al, 2014; Mojid et al, 2015), USA (Irmak et al, 2012) and several regions in China (Ma et al, 2012; Huo et al, 2013; Zhao et al, 2014)
Contrasting result was reported for southern Spain (Espadafor et al, 2011), Greece (Papaioaunou et al, 2011), central Italy (Vergni and Todisco, 2011), Romania (Platineau et al, 2012), Florida (Abtew et al, 2011), central India (Darshana et al, 2012) and Iran (Kousari and Ahani, 2012; Tabari et al, 2012)
Summary
Evapotranspiration is a vital dynamic component of hydrological cycle. Reference crop evapotranspiration (ETo) is a standard for evapotranspiration, which regulates growth and development of crops. The dominant cause of increasing ETo was increased temperature in the Yellow River basin of China (Liu et al, 2010) and Romania (Paltineanu et al, 2012) but increased net radiation in Greece (Papaioaunou et al, 2011). These observations imply that climate change impacts are region-specific. Both under decreasing and increasing ETo, crop-water demand must be adjusted periodically for developing appropriate irrigation scheduling systems. The changes in ETo due to climate change is of great significance in water resource planning for irrigation management and updating climate-change impacts over time
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