Accuracy of air temperature forecasts and its use for prediction of the reference evapotranspiration

Abstract

The objective of this study was to verify the quality of the short-term forecasts made by some web sites, as well as the potential of its use in estimating reference evapotranspiration (ETo). For the period 2012-2013, every 4-days, the maximum (Tmax) and minimum (Tmin) air temperature forecasts for horizons of 24, 48, 72 and 96 hours provided by public sites for Uberlandia-MG were collected and used for calculating the reference evapotranspiration (ETo) by the Hargreaves-Samani (HS) calibrated equation. The sites www.accuweather.com (WEATHER); www.cemig.com.br (CEMIG); jornaldotempo.uol.com.br; (JORNAL) and www.climatempo.com.br (CLIMA) were evaluated. For the same period, the meteorological data were taken at the National Institute of Meteorology (www.inmet.gov.br). The performance of the Tmax and Tmin forecasts as well as the ETo estimates were made by regression analysis, the mean bias error (MBE), root mean square error (RMSE) and t-test. For all sites, there was a better performance in the prediction of Tmin when compared to Tmax, especially by a reduction in errors (MBE and RMSE) and an increase in coefficients b and R². For ETo, the site CLIMA had lowest MBE and RMSE (0.9 mm d^-1) following by the WEATHER and JORNAL. On the other hand, the site CEMIG presented higher values for MBE (-1.3 mm d^-1) and RMSE (1.6 mm d^-1). There was no worsening with an increase of the forecast horizon in these indices, except for R² values. The site CLIMA was the only one that did not differ significantly from the ETo values observed.  The results of diagnostic verification procedures indicate the potential use of air temperature forecasts in irrigation management.