DOWNSCALING BUDYKO EQUATION FOR MONTHLY ACTUAL EVAPOTRANSPIRATION ESTIMATION OVER THE EMILIA-ROMAGNA REGION

: This paper presents a modified Budyko equation (Budyko DOWNSCALED) for assessing actual evapotranspiration (AET0). The approach is tested by using 100 controlled and homogeneous meteorological stations located in the Emilia-Romagna region from North of Italy. A period of 55 years, from 1961-1990 and 1991-2015, was analyzed as long-term datasets of monthly values of precipitations, maximum and minimum temperatures. These data have allowed AET0 to be computed both at the yearly and the monthly scale with the Budyko ORIGINAL and Budyko DOWNSCALED formula, respectively. Results of both methods have been compared at the yearly scale, demonstrating that the Budyko DOWNSCALED approach almost correctly reproduces the annual AET0 values (R 2 equal to 0.77 and 0.73 for 1990s and 2015s, respectively) even if slightly underestimated (by 119 mm for 1990s and by 136 mm for 2015s). Further, monthly AET0 values were aggregated over a baseline period (between 1961 and 1990: 1990s) and a recent period (between 1991 and 2015: 2015s). In both baseline and recent periods, AET0 is higher in the summer months (May to September), while it is almost nil in winter season (January, February, and December). Monthly values of AET0 did not increase over the recent period as a result of increased temperatures. Further, this study contributes to the future management of water resources in the region.

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