Association of Agrometeorologists

Assessing suitability of temperature-based reference evapotranspiration methods for semi-arid basin of Maharashtra

P.S. WABLE, M.K. JHA and S.D. GORANTIWAR

FAO Penman-Monteith (FAO-PM) is deemed as a sole standard method for estimating reference evapotranspiration (ET ). However, limited availability of meteorological data at spatial and temporal o scales restricts the application of this method. To address this issue, the FAO 56 experts suggested three methods when only maximum and minimum temperature data are available: (i) Temperature-based Penman-Monteith (PMT-1) method wherein T ˜ T (ii) PMT-2 wherein T ˜ T -2.5, and (iii) dew min dew min Hargreaves method. These ET methods were assessed for a semi-arid basin of Western India which o lacks adequate climatic data. The performances of the ET methods were evaluated against the standard o FAO-PM method using salient statistical and graphical indicators, together with the sensitivity analysis. The results of the three temperature-based methods had a tendency of over-predication of ET in the o study area. The PMT-1 method, however, provided superior ET estimates compared to PMT-2 and o Hargreaves methods. For estimating monthly ET , the FAO-PM method was most sensitive to o temperature. Further, ET of the monsoon season over the study area increased from 5 to 12% during o 'drought' years compared to 'normal' years. It was concluded that PMT-1 method is the most suitable temperature-based method for estimating ET in semi-arid regions under limited climatic condition.

FAO Penman-Monteith method, temperature-based Penman-Monteith method, Hargreaves method, ET