Evapotranspiration (ET) is a sensitive and integral hydrological and climatic variable in water and energy balance studies. It also holds the second-largest mechanism for precipitation in the hydrological cycle in terms of water quantity and is also a key indicator of climate change and a significant contributing factor to sustainable water resource management as it influences surface water storage; runoff and groundwater recharge. So, environmentalists and researchers have recently paid much attention in detail on the analysis of its temporal trends. In this study, we explore monthly, seasonal and annual trends of both actual evapotranspiration (AET) and potential evapotranspiration (PET) for the area in Son Beel Wetland, Assam using non-parametric Mann–Kendall test and Sen’s slope estimator for the period of 2001–2021. Moderate-resolution imaging Spectroradiometer (MODIS) gap-filled evapotranspiration product of mm/8 day data has been used in this study. The result showed significant increasing trends in AET in June, October, and November. A similar trend is observed in seasonal (spring and autumn seasons) and annual analysis also, the reason being the climate changes that leads to an increase in maximum and minimum temperature. But in the case of PET, there are significant decreasing trends in April, May, and the summer season. The annual analysis shows no significant trend for PET. The results of this analysis will help understand the evapotranspiration dynamics of the study area.