Abstract: The exchanges of heat and water and momentum between land surface and atmosphere are underway con-tinuously. It is important for many actual application questions to measure these quantities, especially sensibleheat and evaporation.At present there are many methods for estimating and calculating sensible heat and evaporation.Among these methods, Bowen ratio energy balance method is most extensively applied. In this paper, the applicability of Bowen ratio energy balance method used in the oasis-desert transitional zones is analyzed fromclimatologic angle.
In the oasis desert transitional zones, although oases and deserts are under the same dry climate environment, in oasis farmland the plant is luxuriant and the soil is damp because of irrigation; but in adjacent desertland the plant is sparse and the soil is dry and hardened. 'T'hey form a strong contrast. Because their natures arecompletely different, it cause the difference of thermodynamic nature and form part of thermodynamic circulation. In suface layer, the cold and wet air stream of oases flows towards deserts; but in the air, the dry airstream of deserts flows towards oases.
Because the cold and wet air stream of oases invades close to surface, it forms a ""cold tongue". In while the air near surface has denatured but the air above surtace has not aenaturea yet nt lor as onre ip asnomenon of positive temperat ure gradient and negative humidity gradient. From these, the results according as Bowen ratio energy balance method are that : the consumed heat for evaporation (the item of LE) is larger than the supportable heat of surface (the item of R-G) and sensible heat transports from atmosphere to surtfacPi I hesedo not accord with the actual situation. It is obvious that the temperature gradient and humidity gradient are caused by the courses of both advection and vertical heat and water transportation. So Bowen ration energy bal-ance method based on the theory of gradient diffusion is invalid in desserts.
The dry and hot air stream is not close to land surface when it enters oases. So in oases, a balance layer isformed. In this layer, the temperat ure gradient and humidity gradient are caused by the course of vertical heatand water transportation. If the heights of measure points are set up in this layer, Bowen ratio energy balancemethod is available but out of this height it is invalid. So in the oasis desert transitional zones, setting measureposition is critical important by using Bowen ratio energy balance method to estimate and calculate ev aporationand sensible heat.

Key words: Bowen ratio energy balance method, climatology oasis, desert