The Reference Evapotranspiration and the Climatic Water Deficit in the Western Plain of Romania, North of the Mure River. In the present paper, reference evapotranspiration (ET0) was calculated by the method proposed by C.W. Thornthwaite. The climatic water deficit, as the difference between atmospheric precipitation and ET0, has also been calculated and analyzed. In this respect, monthly and annual air temperature and precipitation data from 10 weather stations were used. The analysis period was 1961-2002. The result was that the annual average reference evapotranspiration varies, throughout the Western Plain of Romania, North of the Mure River territory, between 665 and 700 mm. It decreases from south to north and also from west to east, depending on the territorial distribution of the air temperature. The plain territory reveals an annual climatic water deficit between 63 mm in the north of the plain and 171 mm in its south. Therefore, the predominantly agricultural territory of the plain needs a water surplus from irrigation. Only in the east of the plain, at Holod, there is a surplus of moisture.