Climate change effects on potential evapotranspiration in Bangladesh

Abstract

Potential evapotranspiration (ETo) is considered to be one of the key factors in water resource practices. Insights into the effects of climate change on ETo are crucial for irrigation design and policy formulation; however, little is understood on it in the case of Bangladesh at the national basin scale. This study intends to appraise monthly, annual, and decadal ETo datasets using the Penman-Monteith FAO-56 (FAO-56 PM) model based on daily meteorological datasets of 25 sites during 1975–2017. The Mann-Kendall (MK) technique was used to detect trend patterns. Besides, Sen’s slope estimator was employed to evaluate the trend lines extent. The results depicted that 82.67% of the monthly ETo values had descending trends and 39.67 and 16.33% were significant at α<0.05 and α<0.01 confidence levels, respectively. By contrast, 17.33% of the monthly ETo value exhibited a significant increasing trend at α<0.05. A significant increasing trend was distributed in the southeastern part of Chittagong, while the decreasing trend was at the southcentral part of Mymensingh (α<0.01). Based on annual and decadal timescales, 92% and 83% of the stations exhibited descending ETo trends in Bangladesh. The ascending trend was observed at Rangamati, Barisal, and Bhola stations, respectively. As a whole, a paradoxical situation may occur due to declining trend patterns of ETo across Bangladesh. This might be due to the decrease in the sunshine hour and wind speed from the impact of the current climate warming. Insights of this research can be used for decision-making for future water resources management in Bangladesh.