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Penman-Monteith, FAO-24 reference crop evapotranspiration and class-A pan data in Australia

1995; Elsevier BV; Volume: 28; Issue: 1 Linguagem: Inglês

10.1016/0378-3774(95)01172-f

1873-2283

Francis H. S. Chiew, N.N. Kamaladasa, Hector Malano, Thomas A. McMahon,

Climate variability and models

The Food and Agriculture Organisation (FAO) methods are recognised as the international standard for estimating reference crop evapotranspiration (ETo). The Penman-Monteith method is currently favoured by the FAO over the FAO-24 methods. The FAO also recommends alternative methods which may be used where there are limited data. In this paper, ETo, estimated using the Penman-Monteith and FAO-24 methods and class-A pan data for 16 Australian locations with a wide range of climate conditions are compared. The analyses indicate that the FAO-24 Penman ETo, estimates are generally 20 to 40% higher than the Penman-Monteith estimates. However, the FAO-24 Radiation and Penman-Monteith methods give similar daily ETo, estimates. Unlike Penman-Monteith, which also requires windspeed data, the FAO-24 Radiation method estimates ETo. from temperature and sunshine hours, climate variables which are relatively conservative in space. The FAO-24 Radiation method can thus be used as a surrogate for Penman-Monteith to estimate daily ETo, for areas where windspeed data are not available. The FAO-24 Blaney-Criddle method, which uses only temperature data, gives similar monthly ETo, estimates as Penman-Monteith, and is therefore adequate for applications where only long-term ETo, estimates are required. The comparisons also show that there is a satisfactory correlation between class-A pan data and Penman-Monteith ETo, for evaporation totals over 3 or more days. However, the pan coefficient is very dependent on local climate and physical conditions, and it should be determined by comparing the pan data with either the Penman-Monteith or FAO-24 Radiation (ETo). estimates.