Publications

This study assesses the accuracy of estimates of FAO Penman-Monteith daily grass reference evapotranspiration (PM-ET_o) using ERA-Interim reanalysis products with 0.75^o x0.75^o spatial resolution. PM-ET_o requires daily maximum and minimum air temperature, net radiation or sunshine duration, relative air humidity or dew point temperature, and wind speed data. For that, local ET_o estimates from 1979-2013 over 37 weather stations distributed across Continental Portugal were compared with those issued from the nearest reanalysis grid-point to each station. Accuracy was assessed using several statistical indicators. Results show that the PM-ET_o computed with raw reanalysis data clearly underestimates (regression slope b₀?1.05) with RMSE exceeding 1.0 mm day^-1 in nearly 30% of cases, but with EF generally above 0.50. Using a monthly bias correction improved the performance of estimates, with b₀ usually close to 1.00, RMSE rarely exceeding 0.80 mm day^-1 , and EF generally above 0.80. These results show that when full local data sets are not available, the PM-ET_o may accurately be computed using daily reanalysis products, thus keeping the ability for the understanding of the physics processes.