Frequency analysis of reference evapotranspiration

The study has been undertaken to determine and evaluate weekly and monthly reference crop evapotranspiration at Akola and Nagpur stations of Vidarbha region. Climatic parameters (Maximum temperature, Minimum temperature, Maximum relative humidity, Minimum relative humidity, Bright sunshine hours, wind speed)for 20 years (1983-2002 )were collected from agriculture meteorological observatory of Akola and Nagpur. Mean climatic data of 20 years (1983-2002) on weekly and monthly basis were used to determine reference evapotranspiration ( ETo) by FAO-56 Penman Monteith method (ETopm) accepted as standard method for estimation of ETo. The frequency analysis has been carried out to select the rate of reference evapotranspiration on probability basis. Commonly used distributions viz. Normal (Gaussian), Log Normal (Log Gaussian), Gamma, Gumbel (Extreme value type I) for maxima & Weibull (Extreme value type III) for maxima ware compared for their suitability in fitting the given data. It is found that no single probability distribution was clearly superior in fitting the data for all meteorological weeks & months of both stations.