EN
Evapotranspiration is the main component of hydrological water cycle at a catchment scale. However it is difficult to estimate the amount of water participating in this process. The issue of estimating the potential evapotranspiration is important from the point of view of hydrological modelling. In this paper we analyzed the potential evapotranspiration at a scale of a large lowland catchment of the Liwiec River in Poland. Data from the MODIS Global Evapotranspiration (PET-MODIS) were used in the analysis covering the period 2001-2010. Monthly and yearly estimates of the PET-MODIS at a catchment scale were compared to the values calculated by the simplified Penman-Monteith equation, according to the FAO methodology, using limited data of air temperature and wind speed. Results have shown that monthly PET-FAO calculated by the simplified Penman-Monteith equation, with limited meteorological data are underestimated with regards to PET-MOD IS. In case of large catchments it is recommended to use in hydrological models such estimates as PET-MODIS, rather than PET values