Evapotranspiration is a critical component of the water balance of a catchment, and riparian zones play a crucial role in the hydrological process. However, the influence of riparian zones on evapotranspiration, especially at a catchment scale, needs more investigation. Since evapotranspiration is negligible at night, the difference in recharge between day and night generates diurnal fluctuations in streamflows. A new method is developed to estimate riparian evapotranspiration by analysing the streamflow response to diurnal evapotranspiration. The potential evapotranspiration (PET) calculated by FAO-56 is used as a true reference for validation. The estimated evapotranspiration shows acceptable goodness of fit with the hourly PET calculated from FAO 56. However, the new approach estimates average evapotranspiration across the entire riparian area than a point observation and provides a better understanding of the impact of the riparian zone on streamflow patterns.