Potential evapotranspiration for the distributed modeling of Belgian catchments

To support a sensitivity analysis in the framework of catchment modeling, three potential evapotranspiration (ET_p) scenarios were generated by means of two Food and Agriculture Organization (FAO) approaches, namely, the FAO-24 and the FAO-56 approaches. The crop ET_p, was estimated as a function of the reference evapotranspiration (ET_o) by means of the k_c-ET_o, approach. Scenario A was generated with the standard FAO-24 approach; Scenario B considered also the FAO-24 approach, but with some nonstandard parameters. Scenario C considered the standard FAO-56 approach. The ET_o data were compared to point-scale ET_o constraints. The annual cumulative value of ET_o from Scenario A was on average approximately 200 mm larger than the values from Scenarios B and C. The research revealed similar ET_o, estimates for Scenarios B and C. The research also assessed the performance of the angstrom approach for estimating incoming solar radiation (R_s). In this context, a set of angstrom coefficients was derived by means of an optimization process that considered available R_s data.