Modelling Spatial-Temporal Pattern of Mountainous Evapotranspiration Based on Altitude Verification

Evapotranspiration (ET) is an important factor in the water balance.About 60% precipitation was depleted by ET while it exceeds 90% in crop land;so it is critical to study the spatial-temporal pattern of ET which will improve the understanding of hydrological process with regard to vegetation change.Thornthwaite model was used to calculate the ET of the upper Minjiang River.A mountainous radiation hour method was employed to improve the model precision.The results show that the verified model error was between 0.13%～20.72%,with a great reduction compared with the unverified model error of 0.72%～46.72%.Although the reduction of error was only 5% on average but it is important to the water cycle.The results also demon- strated that ET changed greatly in the past 30 years.ET was about 300 mm in 1970s while it was about 315.84 mm at the middle of 1980s.However ET decreased to 305.72 mm at the end of 1990s.