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A methodology is proposed to carry out spatio-temporal projections of reference evapo-transpiration (ET0), and to analyse the possible impact of climate change, on semi-arid basins. The study is carried out in the Segura Hydrographic Demarcation, using the Hargreaves model, calibrated monthly following the Allen method, to estimate ET0. The input information is a regionalization of maximum and minimum temperatures based on the global models MPEH5 and MPEH5C and the emission scenarios SRESA2, SRESA1B, SRESB1 and E1. The temporal trend and spatial distribution of ET0 variation were evaluated using the Theil-Sen estimator and Mann Kendall test, and 3 methods of interpolation (multiple linear regression, ordinary kriging and regression-kriging). A significant increase is observed in the 4 scenarios that oscillate between 2.73 mm in SRESA2 and 0.63 mm in E1. There is also a spatial pattern that shows a greater increase in ET 0 in headwaters and a smaller increase in the coastal zone.