FORECASTING OF REFERENCE CROP EVAPOTRANSPIRATION

The first step in the determination of irrigation water requirements f or use in project planning, design, and operation commonly involves th e prediction of the reference crop evapotranspiration. This paper pres ents a simple mathematical model for forecasting reference crop evapot ranspiration at three stations in California that represent humid, sem i-arid, and arid weather conditions, covering three extremes in the Ca lifornia climate. A time domain-time series model is identified for th e reference crop evapotranspiration data at each of the sites and comp ared to other simple methods of forecasting using monthly average and yearly difference approaches. Based on the results of model comparison s it is concluded that a generalized time series model can be used to forecast reference crop evapotranspiration at each of the stations, an d that the time series model can provide a reasonably accurate, yet si mple method of forecasting reference crop evapotranspiration in many a gricultural areas of California.