Regional models of potential evaporation and reference evapotranspiration for the northeast USA

Multivariate regression models of average monthly reference crop evapotranspiration, E(t)(tau), and potential evaporation, E(p)(tau), are developed for the northeast USA. Average monthly values of daily E(t) and E(p) are estimated from the Penman-Monteith equation using monthly climate data from 34 National Oceanic and Atmospheric Administration (NOAA) First Order weather observatories and specific reference vegetation characteristics. The periodic seasonal behavior of E(t)(tau) and E(p)(tau) and average monthly temperature are approximated by Fourier series functions. Regional regression relationships are then developed which relate the E(t)(tau) and E(p)(tau) Fourier series coefficients with the average monthly temperature Fourier coefficients, station longitude and station elevation. The regional E(t)(tau) model is shown to be an improvement over the Linacre method (Linacre, 1977, Agric. Meteorol., 18: 409-424) and the Hargreaves and Samani method (Hargreaves and Samani, 1985, Appl. Eng. Agric., 1(2): 96-99), and the regional E(p)(tau) model is shown to be an improvement over the Linacre method.